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Title: Tropical Cyclogenesis from Self-Aggregated Convection in Numerical Simulations of Rotating Radiative-Convective Equilibrium.
Creator: Carstens, Jacob D., Wing, Allison A., Hart, Robert E. (Robert Edward), Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean...
Show moreCarstens, Jacob D., Wing, Allison A., Hart, Robert E. (Robert Edward), Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Organized convection is of critical importance in the tropical atmosphere. Recent advances in numerical modeling have revealed that moist convection can interact with its environment to transition from a quasi-random to organized state. This phenomenon, known as convective self-aggregation, is aided by feedbacks involving clouds, water vapor, and radiation that increase the spatial variance of column-integrated frozen moist static energy. Prior studies have shown self-aggregation to take...
Show moreOrganized convection is of critical importance in the tropical atmosphere. Recent advances in numerical modeling have revealed that moist convection can interact with its environment to transition from a quasi-random to organized state. This phenomenon, known as convective self-aggregation, is aided by feedbacks involving clouds, water vapor, and radiation that increase the spatial variance of column-integrated frozen moist static energy. Prior studies have shown self-aggregation to take several different forms, including that of spontaneous tropical cyclogenesis in an environment of rotating radiative-convective equilibrium (RCE). This study expands upon previous work to address the processes leading to tropical cyclogenesis in this rotating RCE framework. More specifically, a 3-D, cloud-resolving numerical model is used to examine the self-aggregation of convection and potential cyclogenesis, and the background planetary vorticity is varied on an f-plane across simulations to represent a range of deep tropical and near-equatorial environments. Convection is initialized randomly in an otherwise homogeneous environment, with no background wind, precursor disturbance, or other synoptic-scale forcing. All simulations with planetary vorticity corresponding to latitudes from 10° to 20° generate intense tropical cyclones, with maximum wind speeds of 80 m/s or above. Time to genesis varies widely, even within a 5-member ensemble of 20° simulations, reflecting a potential degree of stochastic variability based in part on the initial random distribution of convection. Shared across this so-called “high-f” group is the emergence of a midlevel vortex in the days leading to genesis, which has dynamic and thermodynamic implications on its environment that facilitate the spinup of a low-level vortex. Tropical cyclogenesis is possible in this model even at values of Coriolis parameter as low as that representative of 1°. In these experiments, convection self-aggregates into a quasi-circular cluster, which then begins to rotate and gradually strengthen into a tropical storm, aided by near-surface inflow and shallow overturning radial circulations aloft within the aggregated cluster. Other experiments at these lower Coriolis parameters instead self-aggregate into an elongated band and fail to undergo cyclogenesis over the 100-day simulation. A large portion of this study is devoted to examining in greater detail the dynamic and thermodynamic evolution of cyclogenesis in these experiments and comparing the physical mechanisms to current theories.
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Date Issued: 2019
Identifier: 2019_Spring_Carstens_fsu_0071N_15075
Format: Thesis

Title: Flash Characteristics and Precipitation Metrics of Western U.S. Lightning-Initiated Wildfires.
Creator: MacNamara, Brittany R., Fuelberg, Henry E., Liu, Guosheng, Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and...
Show moreMacNamara, Brittany R., Fuelberg, Henry E., Liu, Guosheng, Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: The United States Forest Service (USFS) bases their wildfire predictions on cloud-to-ground lightning flash density thresholds greater than 5 fl km-2. High flash densities and low precipitation are often emphasized with storms since they are associated with wildfire ignitions. Yet, greater flash rates tend to occur in the areas of greatest rainfall. This study focuses on 95 lightning-initiated wildfires in the western United States during the year of 2017. Lightning data provided by the...
Show moreThe United States Forest Service (USFS) bases their wildfire predictions on cloud-to-ground lightning flash density thresholds greater than 5 fl km-2. High flash densities and low precipitation are often emphasized with storms since they are associated with wildfire ignitions. Yet, greater flash rates tend to occur in the areas of greatest rainfall. This study focuses on 95 lightning-initiated wildfires in the western United States during the year of 2017. Lightning data provided by the National Lightning Detection Network (NLDN) were analyzed to determine which strike(s) likely caused each fire, as well as the strikes that did not. Detailed analysis of cloud-to-ground lightning characteristics and thunderstorm characteristics such as stroke density, precipitation rate, and 24-h storm-relative QPE totals are presented. Statistical analyses using a Wilcoxon-Mann Whitney rank sum test were performed to reveal differences between lightning flashes that ignite wildfires and those that do not. Results indicate multiple-stroke negative polarity cloud-to-ground flashes dominated the fire starts. In addition, wildfires were initiated in areas with low stroke densities. Based on these tentative findings, the USFS may need to revisit their methods for wildland fire prediction. Rain rates at the locations of fire starts were 8.03 mm h-1 less than those of non-fire starting flashes, while 24-h QPE totals were 5.28 mm less. These differences were found to be statistically significant. The results of this thesis will help expand the limited knowledge of operational lightning and wildfire meteorology. However, considerable additional research is needed.
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Date Issued: 2019
Identifier: 2019_Spring_MacNamara_fsu_0071N_15197
Format: Thesis

Title: Interannual Variability of Tropical Cyclone Potential Intensity and Lifetime Maximum Intensity: An Analysis of Influential Factors.
Creator: Shields, Shannon Rose, Wing, Allison A., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and...
Show moreShields, Shannon Rose, Wing, Allison A., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Many tropical cyclone studies have been conducted on basin-averaged potential intensity trends and the influence of sea surface temperatures (SSTs) on tropical cyclone intensity, but there is less research on along-track potential intensity (PI) and lifetime maximum intensity (referred to here as actual intensity or AI) and the factors that influence their variability. Potential intensity is a theory that predicts the maximum intensity that a tropical cyclone can achieve given certain large...
Show moreMany tropical cyclone studies have been conducted on basin-averaged potential intensity trends and the influence of sea surface temperatures (SSTs) on tropical cyclone intensity, but there is less research on along-track potential intensity (PI) and lifetime maximum intensity (referred to here as actual intensity or AI) and the factors that influence their variability. Potential intensity is a theory that predicts the maximum intensity that a tropical cyclone can achieve given certain large-scale environmental variables. Understanding interannual variability in PI and its relation to AI interannual variability is of great importance for assessing the impact of future climate conditions on tropical cyclones. Theoretically, warmer SSTs and cooler outflow temperatures would cause an increase in overall PI which in turn would lead to an increase in AI. This thesis examined the relationship between PI and AI on interannual time scales and the factors affecting PI variability: thermodynamic efficiency and air-sea enthalpy disequilibrium. Using best-track data and three reanalysis products, variability in PI and AI was examined for the North Atlantic, North Indian, South Indian, South Pacific, Eastern North Pacific, and Western North Pacific basins from 1980-2013. Overall, the Western North Pacific was the only basin that yielded high and consistently significant correlations between AI and PI. Despite the expectation from a previous study, the North Atlantic did not yield robust significant correlations. Multiple tests were then conducted to determine the sensitivity of the North Atlantic correlations to different datasets and time periods. Ultimately, it was determined that the North Atlantic AI vs. PI correlation results were very dependent upon the time period and the individual years within the time period. In the comparison of all contributors, air-sea disequilibrium was the dominant contributor to PI variability. When AI variability was correlated with PI variability, disequilibrium (which is largely controlled by SSTs) was also the dominant contributor to AI variability. Although disequilibrium was the dominant factor in PI and AI interannual variability, efficiency also played a role. In fact, this study found that variances in efficiency explained 13-93% of PI interannual variability, indicating that variability in outflow temperatures (which cause much of the variability in efficiency) must be taken into account.
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Date Issued: 2019
Identifier: 2019_Spring_Shields_fsu_0071N_15097
Format: Thesis

Title: Have Improvements in Ozone Air Quality Benefitted Plants?.
Creator: Ronan, Allison Christine, Holmes, Christopher D., Wing, Allison A., Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and...
Show moreRonan, Allison Christine, Holmes, Christopher D., Wing, Allison A., Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Surface ozone (O3) is a toxic air pollutant. In the United States and Europe, among other places, policies and technology have reduced emissions of O3 precursors the last couple decades. As a result, peak levels of O3, quantified by concentration metrics such as maximum daily average over 8 hours (MDA8), the accumulated O3 exposure over a threshold of 40 ppb (AOT40), and the weighted cumulative exposure index (W126) have fallen. Influential past studies have assumed that these improvements in...
Show moreSurface ozone (O3) is a toxic air pollutant. In the United States and Europe, among other places, policies and technology have reduced emissions of O3 precursors the last couple decades. As a result, peak levels of O3, quantified by concentration metrics such as maximum daily average over 8 hours (MDA8), the accumulated O3 exposure over a threshold of 40 ppb (AOT40), and the weighted cumulative exposure index (W126) have fallen. Influential past studies have assumed that these improvements in AOT40 and W126 imply reductions in plant injury, even though it is widely recognized that O3 flux into leaves is a better predictor of plant damage than ambient concentration in air. Concentration metrics remain widely used because O3 concentration measurements are more common and because concentration and flux are correlated when the variability of stomatal conductance is limited. We use a new dataset of O3 flux into plants to quantify decadal trends in the cumulative uptake of O3 (CUO) into leaf stomata for the first time. We examine 32 sites in the United States and Europe over 2005-2014 and find that the AOT40 and W126 concentration metrics decreased at 25 and 28 sites, respectively, whereas CUO increased at a majority of sites (18). The divergent trends are due to stomatal control of flux, which is shaped by environmental variability. As a result, there has been no widespread, clear improvement in CUO over 2005-2014 at the sites we can assess. We use several statistical tests to show that temporal trends and variability in CUO are uncorrelated with AOT40, W126, and mean concentration (R2 ≤ 0.15). Decreases in concentration metrics, therefore, give a falsely optimistic picture of the direction and magnitude of O3 impacts on vegetation. Because of this lack of relation between flux and concentration, flux metrics should be preferred over concentration metrics in assessments of plant injury from O3. GEOS-Chem is a 3-D global atmospheric chemistry model that uses meteorological input to simulate atmospheric composition. We evaluate the model’s ability to estimate O3 deposition velocity (V_d) by running a simulation during the same period as the surface O3 trend analysis. By comparing monthly output of V_d from GEOS-Chem to our observations using the SynFlux dataset, we find that GEOS-Chem consistently underestimates V_d. The degree of the underestimation depends on the land class type as well as the time of year. We attempt to improve the model output by prescribing the land class type within the model to match the plant functional types at the FLUXNET sites. This did not lead to a significant improvement and in many cases, this led to a wider gap between the model and observations. We discuss possible reasons for the discrepancy between the model and observations. Improving V_d in the model would better estimate dry deposition of O3, which is important for simulating air quality, and its impacts to humans and plants.
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Date Issued: 2019
Identifier: 2019_Spring_Ronan_fsu_0071N_15100
Format: Thesis

Title: Understanding Microphysics of Snowflakes and Snow Precipitation Process Using Spaceborne Microwave Measurements.
Creator: Yin, Mengtao, Liu, Guosheng, Chicken, Eric, Ahlquist, Jon E., Bourassa, Mark Allan, Cai, Ming, Florida State University, College of Arts and Sciences, Department of Earth, Ocean...
Show moreYin, Mengtao, Liu, Guosheng, Chicken, Eric, Ahlquist, Jon E., Bourassa, Mark Allan, Cai, Ming, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Snow, another precipitation form besides rain, affects the Earth’s climate distinctly by modifying hydrological and radiative processes. The radiative properties of nonspherical snowflakes are much more complicated than their spherical counterparts, raindrops. Snowflakes with different structures tend to have different scattering properties. Thus it is important for us to enhance the knowledge in falling snow. However, only a few sensors have been available so far that can provide global...
Show moreSnow, another precipitation form besides rain, affects the Earth’s climate distinctly by modifying hydrological and radiative processes. The radiative properties of nonspherical snowflakes are much more complicated than their spherical counterparts, raindrops. Snowflakes with different structures tend to have different scattering properties. Thus it is important for us to enhance the knowledge in falling snow. However, only a few sensors have been available so far that can provide global snowfall measurements including those onboard he Global Precipitation Measurement (GPM) core observatory and the CloudSat satellites. The GPM satellite carries two important instruments for studying snow precipitations, i.e., the Dual–frequency Precipitation Radar (DPR) and the GPM Microwave Imager (GMI). By combining the GPM instruments with another active sensor onboard the CloudSat satellite, the Cloud Profiling Radar (CPR), an unprecedented opportunity arises for understanding the microphysics of snowflakes and the physical processes of snow precipitation. Seizing this opportunity, in this study, we firstly investigate the microphysical properties of snow particles by analyzing their backscattered signatures at different frequencies. Then, the accuracy of simulating passive microwave brightness temperatures at high frequencies is examined under snowfall conditions using the CPR derived snow water content profiles as radiative transfer model inputs. Lastly, a passive microwave snowfall retrieval method is developed in which the a priori database is optimized by tuning snow water content profiles to be consistent with the GMI observations. To understand the microphysical properties of snow clouds, the triple-frequency radar signatures derived from the DPR and CPR collocated measurements are analyzed. It is noticed that there is a clear difference in triple-frequency radar signatures between stratiform and convective clouds. Through modeling experiments, it is found that the triple-frequency radar signatures are closely related to the size and bulk density of snow particles. The observed difference in triple-frequency radar signatures are mainly attributed to the difference in prevalent particle modes between stratiform and convective clouds, i.e., stratiform snow clouds contain abundant large unrimed particles with low density, while dense small rimed particles are prevalent in convective clouds. To assess the accuracy of radiative transfer simulation for passive microwave high frequency channels under snowfall conditions, we evaluate the biases between observed and simulated brightness temperatures for GMI channels at 166 and 183 GHz. A radiative transfer model is used, which is capable to handle the scattering properties of nonspherical snowflakes. As inputs to the radiative transfer model, the snow water content profiles are derived from the CPR measurements. The results indicate that the overall biases of observed minus simulated brightness temperatures are generally smaller than 1 K except for the 166 GHz horizontal polarization (166H) channel. Large biases for GMI channels are found under scenes of low brightness temperatures. Further investigations indicate that the remaining biases for GMI channels are associated with specific cloud types. In shallow clouds, errors in cloud liquid water profiles are likely responsible for the large positive bias at the 166H channel. In deep convective clouds, strong attenuation in CPR radar reflectivities and possible sampling bias both contribute to the GMI remaining negative biases. A snowfall retrieval algorithm is then developed for GMI observations. The data sources and processing methods are adopted from the above study of GMI bias characterization. First, an a priori database is created which contains the snow water content profiles and their corresponding brightness temperatures simulated for GMI channels. A one–dimensional variational (1D–Var) method is employed to optimize the CPR derived snow water content profiles. The so developed a priori database is applied in a Bayesian retrieval algorithm. The retrieval results show that the 1D–Var optimization can improve the vertical structure of retrieved snow water content. Additionally, this method can bring the global mean distribution of GMI retrieved surface snow water closer to the CPR estimates. This research explores the application of spaceborne microwave measurements to snowfall studies by combining CloudSat and GPM instruments. It provides new knowledge on snowflake microphysics and applicable methods in retrieving three–dimensional snow water distribution from passive high frequency microwave measurements.
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Date Issued: 2019
Identifier: 2019_Spring_Yin_fsu_0071E_14982
Format: Thesis

Title: Impacts of Sugar Cane Agricultural Fires on Air Quality in Southern Florida: Modeling Particulate Matter with the HYSPLIT Atmospheric Dispersion Model.
Creator: Wirks, Charles K., Holmes, Christopher D., Fuelberg, Henry E., Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreWirks, Charles K., Holmes, Christopher D., Fuelberg, Henry E., Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The state of Florida annually approves 7.4×105 hectares (1.8×106 acres) of prescribed fires, and the production of particulate matter (PM) may cause health issues for neighboring communities. Incomplete combustion of biomass leads to the production of abundant amounts of concentrated PM. PM smaller than 2.5 microns in diameter (PM2.5), may have adverse effects on respiratory and cardiovascular health, as shown in earlier studies. Excessive exposure to PM2.5 may lead to diseases such as...
Show moreThe state of Florida annually approves 7.4×105 hectares (1.8×106 acres) of prescribed fires, and the production of particulate matter (PM) may cause health issues for neighboring communities. Incomplete combustion of biomass leads to the production of abundant amounts of concentrated PM. PM smaller than 2.5 microns in diameter (PM2.5), may have adverse effects on respiratory and cardiovascular health, as shown in earlier studies. Excessive exposure to PM2.5 may lead to diseases such as respiratory distress, asthma, heart disease, cancer, and death. In this study, the distribution and effects of PM2.5 caused by prescribed burns of sugarcane crops during the harvest season are simulated and evaluated. This research uses archived data of prescribed fires records from 2008-2015 from the FFS open burn authorizations (OBA). The fires occur during the sugarcane harvest season from Fall (October) until Winter (typically March). We simulate the concentrations of PM2.5 from these fires using the HYSPLIT atmospheric dispersion model driven by meteorology from the North American Mesoscale (NAM) weather model. The results are evaluated against the wind, precipitation, humidity observations, emission factors, locations of fires as reported by Florida Forestry Services (FFS) and observed concentration values reported by the Environmental Protection Agency (EPA). Errors occurred due to the uncertainties and variability in emission factors, fire location, and fire size. The simulation results were then used to evaluate mortality caused by PM2.5 from sugarcane fires in Florida.
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Date Issued: 2019
Identifier: 2019_Summer_Wirks_fsu_0071N_15305
Format: Thesis

Title: Diagnosing the Atmospheric Phenomena Associated with the Onset and Demise of the Rainy Season in Mesoamerica.
Creator: Groenen, Danielle Elizabeth, Bourassa, Mark Allan, Elsner, James B., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences,...
Show moreGroenen, Danielle Elizabeth, Bourassa, Mark Allan, Elsner, James B., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Mexico and Central America (Mesoamerica) are situated in a complex and unique geographical position with the Caribbean Sea to the East and the tropical Eastern Pacific Ocean to the West. The weather patterns of this region are driven by winds, temperatures, moisture, and orography of several mountain ranges. This study finds the dates of the onset and demise of rainfall regimes on a specific day using NASA's Tropical Rainfall Measuring Mission (TRMM) rainfall for years 1998-2012, area...
Show moreMexico and Central America (Mesoamerica) are situated in a complex and unique geographical position with the Caribbean Sea to the East and the tropical Eastern Pacific Ocean to the West. The weather patterns of this region are driven by winds, temperatures, moisture, and orography of several mountain ranges. This study finds the dates of the onset and demise of rainfall regimes on a specific day using NASA's Tropical Rainfall Measuring Mission (TRMM) rainfall for years 1998-2012, area-averaged over land. Using NASA's MERRA-2 Reanalysis data, we also look at the phenomenology of the triggers of the rainy season onset and demise on the daily time-scale instead of the monthly scales used by previous studies. We find that the Mesoamerican Rainy Season can be distinguished into two parts: the Early Spring Rainfall (ESR) associated with light rains and the Late Spring Rainfall (LSR) associated with heavy rains. Two algorithms are used to obtain these rainy season distinctions. A new algorithm was developed during this study, called the SLOPE algorithm, to calculate when the rain rates first start to increase. In the second method, the daily cumulative anomalies of rainfall are compared to the climatological rainfall to find the time of onset of the heavy rains, called the MINCA algorithm. To better understand the phenomenology associated with the timing of the rainfall, we look at the monsoon trough, moisture flux convergence, moist static energy anomalies, and the weakening/strengthening of the winds associated with the Caribbean Low-Level Jet and Panama Jet. The light rain rates begin, on average, in mid-March, approximately one month after the peak of the winter Caribbean Low-Level Jet and the Panama Jet. The ramp-up between the light rains and heavy rains is associated with a significant weakening of both jets and the northward progression of a monsoon trough off the western coast of Central America. The heavy rain rates begin, on average, in mid-May, and are associated with the timing when the Panama Jet goes to near zero magnitude and a strong monsoon trough in the eastern Pacific. At the demise of the rainfall, approximately in mid-November, the Panama Jet strengthens again, the total moisture flux convergence decreases significantly, and the monsoon trough retreats southward and eastward. The results of this study have positive implications in agriculture and water resources for Mesoamerica, as this information may help resource managers better plan and adapt to climate variability.
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Date Issued: 2019
Identifier: 2019_Summer_Groenen_fsu_0071E_15282
Format: Thesis

Title: An Absolute Angular Momentum Based Analytical Model for Tropical Cyclone Radial Wind Profiles.
Creator: Yan, Ruikai, Cai, Ming, Niu, Xufeng, Chagnon, Jeffrey M., Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreYan, Ruikai, Cai, Ming, Niu, Xufeng, Chagnon, Jeffrey M., Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The ability to construct radial wind profiles of tropical cyclones (TC) from limited observations is crucial to the initialization of TC simulations and predictions. A minimum requirement for constructing a reasonable radial wind profile is a high skill in estimating one of the four TC characteristic parameters, namely maximum wind speed (Vmax), radius of maximum wind speed (rmax), 17 ms−1 wind speed (V17), and radius of 17 ms−1 wind (r17) from the other three. In this study, we put froth an...
Show moreThe ability to construct radial wind profiles of tropical cyclones (TC) from limited observations is crucial to the initialization of TC simulations and predictions. A minimum requirement for constructing a reasonable radial wind profile is a high skill in estimating one of the four TC characteristic parameters, namely maximum wind speed (Vmax), radius of maximum wind speed (rmax), 17 ms−1 wind speed (V17), and radius of 17 ms−1 wind (r17) from the other three. In this study, we put froth an absolute angular momentum (AAM) based analytical model for inferring the radial profile beyond the rmax from observations of these four parameters. An observed AAM loss L is defined as the ratio of the observed AAM at r17 to that at rmax. We parameterize the observed AAM loss L as an analytical function of these four parameters and environmental factors. The combination of analytical expressions of the AAM loss L and the AAM at r17 and rmax, gives us the analytical model. This observation-physics model allows us to construct radial profiles of TCs under four different configurations from observations of these four parameters. Specifically, we can use Vmax and rmax as inputs for solving (a) the tangential velocity profile of a TC from rmax to r17 or (b) the TC's radius for a given tangential velocity from Vmax to V17. Alternatively, we can use V17 and r17 as inputs for solving (c) the tangential velocity profile of a TC from r17 to rmax or (d) the TC's radius for a given tangential velocity from V17 to Vmax. This enables us to acquire radial wind profiles when one of the four parameters is not available in observations. The degree of consistency of (a) versus (c) and (b) versus (d) is an indicator of the robustness of the model. We evaluate the skill of our model using 4491 records of 197 named TCs derived from the Extended Best Track Dataset for the period of 1998-2016, and find that the mean errors in estimating Vmax, rmax, V17, and r17 are, respectively, 5.95 m/s, 25.37 km, 3.33 m/s, and 57.67 km. The proposed model has several advantages over widely recognized existing TC wind profile models. Most empirical models, for example, are designed to construct radial wind profiles in only one of the four configurations. While other physics-based models have mean errors in Vmax, rmax, and r17 that are larger by several factors. Furthermore, our model can yield physically realistic radial wind profiles and solutions of TC characteristic parameters (meaning that for radial wind profiles, wind velocity decreases monotonically from rmax to r17, and for solutions, Vmax > V17 > 0 and r17 > rmax > 0) for all 4491 TC records, regardless of which of the four configurations is chosen. For more than 10% of the TC records, however, other physics-based models have radial wind profiles that are discrete or increases from the inside to outside, and have solutions that either do not exist or are not physical under certain configurations.
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Date Issued: 2019
Identifier: 2019_Summer_Yan_fsu_0071E_15321
Format: Thesis

Title: Climate Variability of the Arctic from an Isentropic Potential Vorticity Perspective.
Creator: Haynes, Brian Joshua, Chassignet, Eric P., Bourassa, Mark Allan, Dukhovskoy, Dmitry, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth,...
Show moreHaynes, Brian Joshua, Chassignet, Eric P., Bourassa, Mark Allan, Dukhovskoy, Dmitry, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The background state of the Arctic atmosphere under prolonged warming is analyzed by evaluating blended CFSR-CFSv2 reanalysis data from an isentropic lens, where potential temperature is used as the vertical coordinate and the principle dynamical framework is potential vorticity (PV). Since the quantity is materially conserved along adiabatic, friction-less flow, PV can be used to describe the background vorticity and static stability as well as to give insight on how diabatic processes might...
Show moreThe background state of the Arctic atmosphere under prolonged warming is analyzed by evaluating blended CFSR-CFSv2 reanalysis data from an isentropic lens, where potential temperature is used as the vertical coordinate and the principle dynamical framework is potential vorticity (PV). Since the quantity is materially conserved along adiabatic, friction-less flow, PV can be used to describe the background vorticity and static stability as well as to give insight on how diabatic processes might alter this balance. Of particular interest is how the background state of the lower troposphere has evolved in recent years to become preferential to inducing anticyclonic wind stress at the Arctic ice-ocean surface. We compare the trends in Arctic PV to the Arctic Ocean Oscillation (AOO), which entered a phase of a dominantly anticyclonic circulation of the Beaufort Gyre (BG) in the mid-to-late 1990's and has persisted since. We find that PV has a relationship with sea surface height (SSH), which in turn can be used to quantify the index of the AOO, and that the strongest relationship occurs during the ice melt season. The reduced meridional thermal gradient during the ice melt season, here designated as the summer (JJA) and autumn (SON) seasons, allows for increased meridional transport of mid-latitude air masses. This is quantified by correlating melt season PV flux and the surface heat budget as well as wintertime geopotential height and zonal wind to connect the background environment preceding the peak Arctic Oscillation (AO) signal, which can enhance or suppress the typical sea level pressure (SLP) maximum that exists over the Beaufort Sea during this time. We find that positive meridional fluxes of PV during summer correlate with increased net shortwave fluxes at the surface and increased outgoing longwave fluxes in autumn. The relationship between the influx of low-latitude PV and the surface heat budget is consistent with previous works that demonstrate the role Arctic cyclones have on sea ice transport, which has major implications on the absorption and release of heat to and from the Arctic Ocean. The transport of lower-PV air associated with latent heat release via saturation of air parcels and higher specific humidity modulates the environmental PV, stabilizing the boundary layer and reducing the cyclonic tendency over the Beaufort Sea region. This may have further impacts in reducing the baroclinicity of the Arctic and suppress cyclonic development during fall, which in return may promote conditions favorable to downwelling earlier that promote an anticyclonic ocean current to develop and persist for much of the year.
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Date Issued: 2019
Identifier: 2019_Fall_Haynes_fsu_0071N_15583
Format: Thesis

Title: Atlantic Tropical Cyclone Interactions with Upper Tropospheric Flow: Identification, Climatology, and Modulation of Tropical Cyclone Intensity.
Creator: Cowan, Levi, Hart, Robert E. (Robert Edward), Harper, Kristine, Chagnon, Jeffrey M., Sura, Philip, Misra, Vasubandhu, Florida State University, College of Arts and Sciences,...
Show moreCowan, Levi, Hart, Robert E. (Robert Edward), Harper, Kristine, Chagnon, Jeffrey M., Sura, Philip, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Interactions of Atlantic tropical cyclones (TCs) with upper tropospheric flow are identified in 37 years of ERA-Interim reanalysis data and analyzed from multiple perspectives. Upper tropospheric troughs are identified in a more comprehensive way than past methodologies, targeting features on the dynamic tropopause to reduce exclusivity of feature selection and sensitivity to the background environment. To overcome some limitations of the trough perspective, a new approach to analyzing TC...
Show moreInteractions of Atlantic tropical cyclones (TCs) with upper tropospheric flow are identified in 37 years of ERA-Interim reanalysis data and analyzed from multiple perspectives. Upper tropospheric troughs are identified in a more comprehensive way than past methodologies, targeting features on the dynamic tropopause to reduce exclusivity of feature selection and sensitivity to the background environment. To overcome some limitations of the trough perspective, a new approach to analyzing TC-environment interactions is developed through the identification of upper tropospheric jets near TCs. Jet axes are identified in 200-hPa wind fields within 3000 km of TCs using a robust, objective algorithm, forming a novel dataset that provides a unique way of characterizing and subsetting environmental flow. The climatology of these jets is explored through various means, including an objective clustering technique, which yielded seven statistically distinct groups of jets associated with recognizable flow patterns near TCs. The dynamical coupling between TCs and nearby jets is also quantified, with acceleration of jets downstream of the TC found to be a nearly ubiquitous feature, and entrance regions of jet streaks are observed to significantly enhance the strength of the TC secondary circulation. The influence of nearby upper tropospheric troughs and jets on TC intensity is also assessed through a variety of approaches. In order to minimize systematic sampling biases when quantifying this impact, a spatially varying climatology of TC intensification rate is developed using a second-order, generalized least squares regression model, allowing TC intensity responses to external forcing to be evaluated as departures from their expected value. Both troughs and jets are found to be net negative influences on TC intensity, on average, primarily due to increasing vertical shear with proximity to the vortex. Differences between rapidly intensifying (RI) and rapidly weakening (RW) cases during TC-trough-jet interactions depend not only on shear, but on dynamic forcing imposed by baroclinic processes and eddy momentum fluxes that can counter the influence of shear. Intensifying cases are primarily associated with jets that approach the poleward side of the TC and possess jet streaks that amplify over time, increasing dynamic forcing for ascent near the TC core while maintaining enough distance to prevent shear from overwhelming those effects. This study expands the set of tools for analyzing TC interactions with upper tropospheric flow by improving trough identification and introducing a new perspective through the use of jets. Jets afford greater specificity in describing environmental flow, and allow unique methods of quantifying its impact on TCs. Close links are found between jet proximity and vertical shear, as well as jet acceleration and dynamically-forced ascent, both relationships that have been physically understood, but until now unidentified in bulk observational datasets. Some measures of jet entrance region orientation are found to correlate with the relative magnitude of shear and baroclinic forcing, exposing the subtlety in how flow geometries differ between intensifying and weakening TC cases. Prior research has tended to evaluate upper tropospheric influences on TCs individually or relied on case studies to elucidate their collective impact on a single storm. This body of work seeks to illuminate relationships between TCs and upper tropospheric flow that are robust across large samples of TCs and storm environments, utilizing novel approaches such as the jet perspective to extract previously unquantified information.
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Date Issued: 2019
Identifier: 2019_Fall_Cowan_fsu_0071E_15521
Format: Thesis

Title: A Climatology of U.S. Tropical Cyclone Rainfall, Its Use in a Statistical Forecasting Technique and an Analysis of Global Forecast System Tropical Cyclone Rainfall Forecast Environments.
Creator: Hall, Tristan J., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: While advances in tropical cyclone (TC) track forecasting have been substantial over the past few decades, and modest advances in intensity forecasting have occurred more recently, the quality of TC rainfall forecasts has not undergone the same rigorous verification. This is despite the 27% of total TC-related deaths being due to rainfall-induced flooding and that rainfall-related deaths occur more frequently than those due to any another weather-related hazard. A continual effort is needed...
Show moreWhile advances in tropical cyclone (TC) track forecasting have been substantial over the past few decades, and modest advances in intensity forecasting have occurred more recently, the quality of TC rainfall forecasts has not undergone the same rigorous verification. This is despite the 27% of total TC-related deaths being due to rainfall-induced flooding and that rainfall-related deaths occur more frequently than those due to any another weather-related hazard. A continual effort is needed to understand and better-forecast TC rainfall. This dissertation research seeks to contribute to this endeavor. A climatological dataset is created using 6-h Stage IV rainfall accumulations combined with Best Track 6-h locations for all TCs within 300 km of the U.S. Gulf and Atlantic coastlines during years 2004 - 2013. Stage IV data are used due to their higher spatiotemporal resolution, their extension to high latitudes, and because they have been found to be the superior option when compared to other TC rainfall data sources. The 6-h Stage IV rainfall accumulations are composited by shear magnitude and storm intensity in earth-, motion-, and shear-relative reference frames. Additionally, a full composite comprised of all storms is created. This compositing is done for TCs impacting the U.S. Gulf and Atlantic coastlines. Seven geographical regions are created within this domain to further composite the rainfall. The geographical regions are determined based on 2004 - 2013 Best Track (HURDAT2) landfall locations. Results show that some Stage IV rain rate characteristics, especially those in specific regions, are different when compared to prior findings based on satellite-derived rain rates. Results from the Stage IV-derived climatological datasets then are used together with track forecasts from the Global Forecast System (GFS) during years 2014 - 2016 to create 72-h TC rainfall forecasts. Separate forecasts are created for each 6-h TC position forecast based on shear magnitude, storm intensity, and the all-storms composites in earth-, motion-, and shear-relative reference frames. This yielded 1,290 verifiable forecasts during the 3-yr period. These statistical rainfall forecasts along with forecasts from the GFS and an R-CLIPER created from Stage IV data are verified using the Fractions Skill Score (FSS) metric. Results show that the statistical method based on shear magnitude in a shear-relative reference frame that used regional rainfall composites is the best performing of the methods. Additionally, FSSs from the statistical model are shown to be larger than those from R-CLIPER. The preliminary results from the statistical model show that this method is a viable candidate to supplement R-CLIPER as a statistical baseline TC rainfall forecast method. GFS analysis and forecast environmental parameters are composited based on the skill (FSS) of each forecast. Three categories are created: Top (FSS > 0.6), Bottom (FSS < 0.3), and Middle (0.3 < FSS < 0.6). This methodology is based on the desire to provide "guidance on guidance," i.e., suggesting to a forecaster whether the TC's environment is conducive to a skillful or not-skillful GFS rainfall forecast, and to help determine possible factors to increase the FSS of the statistical model. Results show that some aspects of the mean sea level pressure, 1000 - 500 hPa thickness anomalies, eddy flux convergence, and upper-level winds and divergence differ between skillful and non-skillful TC rainfall forecasts.
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Date Issued: 2019
Identifier: 2019_Fall_HALL_fsu_0071E_15343
Format: Thesis

Title: HWRF Analysis and Forecast Impact of CYGNSS Observations Assimilated as Scalar Wind Speeds and as VAM Wind Vectors.
Creator: Annane, Bachir, Liu, Guosheng, Krishnamurti, Ruby, Wang, An-I Andy, Misra, Vasubandhu, Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department...
Show moreAnnane, Bachir, Liu, Guosheng, Krishnamurti, Ruby, Wang, An-I Andy, Misra, Vasubandhu, Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: After decades of focused research into tropical cyclone (TC) dynamics and evolution, operational centers are now able to predict TC track out to a lead time of five days with a high degree of accuracy. However, during this time, forecast skill for TC intensity has not kept the same pace. There are likely many reasons for this slowing improvement in TC intensity forecasts, but the one that is cited often in the community is a lack of frequent and accurate observations of winds in the inner...
Show moreAfter decades of focused research into tropical cyclone (TC) dynamics and evolution, operational centers are now able to predict TC track out to a lead time of five days with a high degree of accuracy. However, during this time, forecast skill for TC intensity has not kept the same pace. There are likely many reasons for this slowing improvement in TC intensity forecasts, but the one that is cited often in the community is a lack of frequent and accurate observations of winds in the inner core of TCs. Specifically, current satellite observing systems are unable to penetrate through heavy rainfall, and in situ measurements by aircraft and dropsondes are limited in space and time. The paucity of observations of surface wind speeds in the most dynamically active portion of a TC leads to (1) inaccuracies in the initial conditions used in subsequent model forecasts and (2) insufficient information for evaluating parameterizations of convection and surface fluxes. The NASA Cyclone Global Navigation Satellite System (CYGNSS) mission is designed to address these shortcomings by providing more accurate and timely observations of surface winds in all precipitation conditions. Eight micro-satellites launched in December 2016 (CYGNSS), providing an unprecedented opportunity to obtain ocean surface wind at increased revisit frequency compared to polar-orbiting satellites. Release 2.1 of the CYGNSS data contain improved wind speed quality and can be used to run data impact studies for the cases where the operational center had a weak intensity forecast. This study explores the expected benefits of this retrieved data to numerical simulations of tropical cyclones using two different data assimilation methods within the experimental framework of Observing System Simulation Experiments (OSSE) and Observing System Experiments (OSE). The goals of this study are three-fold: first, investigate the potential for CYGNSS to improve analyses and forecasts of tropical cyclones in an OSSE framework (pre-Launch); second, application of the variational analysis method (VAM) method on the CYGNSS data; third, evaluate the actual influence of assimilating CYGNSS data into NOAA’s operational hurricane model (Post-Launch). From a highly detailed and realistic hurricane nature run (NR), CYGNSS winds were simulated with error characteristics that are expected to occur in reality, and directional information is added using a two dimensional VAM for near-surface vector winds that blends simulated CYGNSS wind speeds with an a priori background vector wind field at 6-h analysis times. The OSSE system makes use of NOAA’s Hurricane Weather and Research Forecast (HWRF) model and Gridpoint Statistical Interpolation (GSI) data assimilation system in a configuration that was operational in 2012. CYGNSS winds were assimilated as scalar wind speeds and as wind vectors determined by a variational analysis method. Both forms of wind information had positive impacts on the short-term HWRF forecasts, as shown by key storm and domain metrics. Data assimilation cycle intervals of 1, 3, and 6 hours were tested, and the 3-h impacts were consistently best. The OSE quantifies the impact of assimilating both CYGNSS retrieved wind speed and derived CYGNSS wind vectors in tropical cyclone Michael (2018) on 6-hourly analyses and 5-day forecasts, using the 2019 version of the operational HWRF model. It is found that the assimilation of CYGNSS data results in improved track, intensity, and structure forecasts for both retrieved and derived CYGNSS data, implying the potential benefits of using such data for future research and operational applications.
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Date Issued: 2019
Identifier: 2019_Fall_Annane_fsu_0071E_15536
Format: Thesis

Title: Ice versus Liquid Water Saturation in Regional Climate Simulations of the Indian Summer Monsoon.
Creator: Glazer, Russell Henderson, Misra, Vasubandhu, Shanbhag, Sachin, Bourassa, Mark Allan, Hart, Robert E., Liu, Guosheng, Florida State University, College of Arts and Sciences,...
Show moreGlazer, Russell Henderson, Misra, Vasubandhu, Shanbhag, Sachin, Bourassa, Mark Allan, Hart, Robert E., Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: At the same temperature, below 0oC, the saturation vapor pressure (SVP) over ice is slightly less than the SVP over liquid water. Numerical models use the Clausius-Clapeyron relation to calculate the SVP and relative humidity, but there is not a consistent method for the treatment of saturation above the freezing level where ice and mixed-phase clouds may be present. In the context of current challenges presented by cloud microphysics in climate models, we argue that a better understanding of...
Show moreAt the same temperature, below 0oC, the saturation vapor pressure (SVP) over ice is slightly less than the SVP over liquid water. Numerical models use the Clausius-Clapeyron relation to calculate the SVP and relative humidity, but there is not a consistent method for the treatment of saturation above the freezing level where ice and mixed-phase clouds may be present. In the context of current challenges presented by cloud microphysics in climate models, we argue that a better understanding of the impact that this treatment has on saturation-related processes like cloud formation and precipitation, is needed. This study explores the importance of the SVP calculation through model simulations of the Indian Summer Monsoon (ISM) using atmosphere-only simulations with the Regional Spectral Model (RSM) and RSM coupled to the Regional Ocean Modeling System (RSM-ROMS). Atmosphere-only simulations are conducted with two saturation parameterizations. In one, the SVP over liquid water is prescribed through the entire atmospheric column (woIce), and in another the SVP over ice is used above the freezing level (wIce). When SVP over ice is prescribed, a thermodynamic drying of the middle and upper troposphere above the freezing level occurs due to increased condensation. In the wIce runs, the model responds to the slight decrease in the saturation condition by increasing, relative to the SVP over liquid water only run, grid-scale condensation of water. Changes in the cloud layer amounts in the wIce simulation cause in increase in the net heat flux (NHF) at the surface of 2-3 W/m2 over the Arabian Sea (AS) and a decrease of similar magnitude over the eastern equatorial Indian Ocean (EEIO). Motivated by these NHF changes the wIce and woIce experiments were repeated in the coupled simulations. With coupling added, the ocean is allowed to respond to any NHF changes; however we find that the NHF difference between wIce-woIce over the AS is near zero. It is proposed that with the inclusion of air-sea coupling the atmospheric and oceanic response to changes in the SVP is damped relative to the forced RSM integrations. The importance of air-sea interaction for the northward propagation and evolution of the Indian monsoon intrareasonal oscillation (ISO) is examined through a comparison between the uncoupled and coupled simulations, and the observed ISO. It was found that the observed ISO contains a robust air-sea interaction during its evolution which would suggest that coupling is required to simulate the observed relationship between the ocean and atmosphere during the ISO. However, the uncoupled simulations show the ability to simulate realistic amplitude ISOs without coupling to the ocean, suggesting that there is an internal atmospheric component that is important for simulating the observed ISO period and amplitude.
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Date Issued: 2018
Identifier: 2018_Sp_Glazer_fsu_0071E_14515
Format: Thesis

Title: Analysis of the 10–20-Day Intraseasonal Oscillation in the Indian Ocean Using Surface Winds from Composite Satellite Data.
Creator: Roman-Stork, Heather Leigh, Bourassa, Mark Allan, Misra, Vasubandhu, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and...
Show moreRoman-Stork, Heather Leigh, Bourassa, Mark Allan, Misra, Vasubandhu, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: The 10–20-day mode of surface winds is examined in the Indian Ocean, with special reference to the Arabian Sea, the Bay of Bengal, and the equatorial Indian Ocean during a strong (1994), weak (2002), and normal (1995) Indian summer monsoon. The winds are from the Cross Calibrated Multi-Platform (CCMP) gridded wind product version 2.0. Results indicate the 10–20-day mode of latitudinally averaged surface winds have zonal propagation in the western Indian Ocean (west of 75°E) and the signal...
Show moreThe 10–20-day mode of surface winds is examined in the Indian Ocean, with special reference to the Arabian Sea, the Bay of Bengal, and the equatorial Indian Ocean during a strong (1994), weak (2002), and normal (1995) Indian summer monsoon. The winds are from the Cross Calibrated Multi-Platform (CCMP) gridded wind product version 2.0. Results indicate the 10–20-day mode of latitudinally averaged surface winds have zonal propagation in the western Indian Ocean (west of 75°E) and the signal appears stationary in the eastern Indian Ocean (east of 75°E) during May through September. The meridional propagation of the 10–20-day mode of longitudinally averaged surface winds appears weak during summer monsoon periods. The 10–20-day mode of surface winds in the Arabian Sea and the Bay of Bengal is more energetic than in the equatorial Indian Ocean. The signal of the 10–20-day mode appears more robust during a strong monsoon than during a weak monsoon in the Arabian Sea; however, no significant difference is found in the Bay of Bengal and equatorial Indian Ocean between strong and weak monsoons. Ensemble empirical mode decomposition (EEMD) analysis is used on a time series from the Arabian Sea to create an index for the 10–20-day mode in surface winds. Using this index, 75 cases of 15-phase 10–20-day events are identified and used to create composites of surface winds. Through these composites, a positive surface wind anomaly is found to appear at 60°E, centered on 15°S, and propagate zonally eastward to 90°E before reflecting back to propagate westward and then disperse off the coast of Madagascar. It is proposed that this oscillating positive wind anomaly is a feature of the southernmost cell of the 10–20-day convective double-cell structure that has extended farther south into the southern Indian Ocean and that this mode connects the Arabian Sea and southern Indian Ocean through the Somali Jet and surface winds.
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Date Issued: 2018
Identifier: 2018_Su_RomanStork_fsu_0071N_14803
Format: Thesis

Title: The African Easterly Jet: Double Core Structure and Effect on Easterly Wave Development.
Creator: Hosten, Amana, Nicholson, Sharon E., Chagnon, Jeffrey M., Hart, Robert E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric...
Show moreHosten, Amana, Nicholson, Sharon E., Chagnon, Jeffrey M., Hart, Robert E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: The African Easterly Jet (AEJ) is one of the phenomena driving regional as well as global atmospheric circulation. Specifically, within the Sahel region, the AEJ and African Eastern Waves (AEWs) are main features that are linked and associated with the West African Monsoon. Both features determine rainfall and tropical cyclone development in this region. For certain years, the AEJ has a double core structure during the month of August when the jet is the strongest. The goal of this study is...
Show moreThe African Easterly Jet (AEJ) is one of the phenomena driving regional as well as global atmospheric circulation. Specifically, within the Sahel region, the AEJ and African Eastern Waves (AEWs) are main features that are linked and associated with the West African Monsoon. Both features determine rainfall and tropical cyclone development in this region. For certain years, the AEJ has a double core structure during the month of August when the jet is the strongest. The goal of this study is to identify distinct cases of the AEJ structure and determine the possible effect on AEW development. For this study, zonal and meridional wind data at 600 hPa was obtained from NCEP reanalysis during the month of August from 1948 to 2016. Maps of zonal wind were made to show the structure of the AEJ. Hovmöller diagrams of the 2.5 to 6-day meridional wind and maps of meridional wind variance were made to show the strength and track of AEWs. Results identified distinct cases where the structure of the AEJ deviated from its long-term mean, including the western (eastern) core being located north relative to the eastern (western) core. The double core cases with the southward eastern core has significantly stronger AEW activity with longer average tracks. However, on inter-annual scales, there is not a strong link between the AEW activity and east Atlantic tropical cyclone activity. The difference between the cases provide valuable insight about the relationship between the AEJ, easterly waves and tropical cyclone formation at the West African coast.
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Date Issued: 2018
Identifier: 2018_Su_Hosten_fsu_0071N_14570
Format: Thesis

Title: Florida's Tornado Climatology: Occurrence Rates, Casualties, and Property Losses.
Creator: Ryan, Emily, Elsner, James B., Folch, David C., Horner, Mark W., Florida State University, College of Social Sciences and Public Policy, Department of Geography
Abstract/Description: Florida has a high frequency of tornadoes that occur throughout the United States. Together, Florida's large population and expensive property, provides a great risk for injuries, fatalities, and damage to structures for when a tornado occurs. This risk of death or damage continues to increase as the population expands. The goal of this research is to better understand the tornado hazard in Florida by creating a climatology of Florida tornadoes through examining occurrence rates, casualties,...
Show moreFlorida has a high frequency of tornadoes that occur throughout the United States. Together, Florida's large population and expensive property, provides a great risk for injuries, fatalities, and damage to structures for when a tornado occurs. This risk of death or damage continues to increase as the population expands. The goal of this research is to better understand the tornado hazard in Florida by creating a climatology of Florida tornadoes through examining occurrence rates, casualties, and property loss. The tornado reports are obtained from the Storm Prediction Center's Severe Weather database. Descriptive statistics are used to analyze temporal distributions, characteristics, and geographical distributions of tornadoes. Tropical cyclone tornado data from 1995 through 2013 is used for examining temporal distributions throughout the state. In addition, a new property value dataset put together by Georgianna Strode at the Florida Resources and Environmental Analysis Center is used to evaluate property loss from tornadoes throughout the state. Inferential statistics are used for testing hypotheses and modeling future tornado paths using a Monte Carlo simulation. Over the period from 1987 though 2016, there were 1,765 tornado reports in the state. The peak frequency occurs during the month of June with the overall tornado distribution mimicking the tropical cyclone distribution of the North Atlantic hurricane season. Majority of tornadoes occur in the peninsular region of the state, with tornadoes in the panhandle likely being stronger. There is a strong positive correlation between the amount of property exposed and the number of casualties produced by tornadoes. Although the majority of tornadoes that occur throughout Florida are very weak, the path length and width are shown to be increasing in recent years. Additionally, the annual average property loss estimate from tornadoes in Florida is $53 Million. Results of the Monte Carlo simulation indicate a 5% chance that the annual loss will exceed $203 million, a 1% chance that it will exceed $430 million, and a 0.1% chance that it will exceed $1 billion.
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Date Issued: 2018
Identifier: 2018_Sp_Ryan_fsu_0071N_14554
Format: Thesis

Title: On the Structure and Frequency of Secondary Eyewall Formation in HWRF Simulations of Tropical Cyclone Harvey (2017).
Creator: Di Catarina, Federico, Chagnon, Jeffrey M., Hart, Robert E., Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric...
Show moreDi Catarina, Federico, Chagnon, Jeffrey M., Hart, Robert E., Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Hurricane Harvey (2017) spawned from a westward propagating tropical wave in the Atlantic and then tracked across the southern Caribbean Sea, the Yucatán Peninsula, and lastly over the Gulf of Mexico, where it quickly intensified into a category 4 (on the Saffir-Simpson Scale) tropical cyclone. As a mature hurricane, Harvey underwent an eyewall replacement cycle which led to structural and intensity changes hours before making landfall over the Texas central coast. This study investigates the...
Show moreHurricane Harvey (2017) spawned from a westward propagating tropical wave in the Atlantic and then tracked across the southern Caribbean Sea, the Yucatán Peninsula, and lastly over the Gulf of Mexico, where it quickly intensified into a category 4 (on the Saffir-Simpson Scale) tropical cyclone. As a mature hurricane, Harvey underwent an eyewall replacement cycle which led to structural and intensity changes hours before making landfall over the Texas central coast. This study investigates the structure and frequency of secondary eyewalls in 20 forecast simulations of Tropical Cyclone Harvey (2017) as produced by the 2017 operational Hurricane Weather Research and Forecast (HWRF) System. To understand the predictability of secondary eyewalls, the secondary eyewall-producing simulations must be distinguished from the non-secondary eyewall-producing simulations. Thus, a diagnostic method of subjectively detecting secondary eyewalls in forecast data is developed. The diagnostic method identifies specific secondary eyewall traits that have been studied and documented in literature. The results show that most of the simulations (~80%) produce a secondary eyewall. While the all secondary eyewall-producing simulations are initialized over the ocean, the unsuccessful simulations, on the other hand, are initialized over or just west of the Yucatán Peninsula. To study the relationship between land-storm interaction and secondary eyewall simulation, a comparison is made between the successful simulations initialized over the Caribbean Sea (which tracked over the Yucatán Peninsula) and the unsuccessful runs. For both sets of simulations, the effect of land-storm interaction led to temporary storm weakening while over the Yucatán Peninsula. However, this interaction has respectively a greater negative effect on vortex spin-up and organization on those simulations initialized over land. A comparison between the over land evolution of a non-SE producing and aSE-producing simulation is made. The results show that both storms maintain a similar dynamic structure as they move west over the Yucatán Peninsula. However, the SE-producing simulation is in a more favorable thermodynamic environment with higher RH values above the storms and more convective activity near its center when compared to the non-SE producing simulation. Based on these results, it is speculated that deep moist convective feedback processes enhanced by a thermodynamically favorable conditions within and near the Caribbean Sea initialized storms act as an additional intensification mechanism which lacks in the over land initialized storms. The relatively drier air mass and less convective activity associated with the land simulations produces a less favorable environment and limits the intensification rate of these storms over once over water. It is speculated that slower intensification rates inhibit these storms from reaching an adequate TC intensity and structure conducive for SEF before making landfall over Texas/Mexico and weakening.
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Date Issued: 2018
Identifier: 2018_Fall_DiCatarina_fsu_0071N_14783
Format: Thesis

Title: Two-Way Feedback between Air-Sea Turbulent Fluxes and Oceanic Submesoscale Processes.
Creator: Chen, Xu, Dewar, William K., Chassignet, Eric P., Tam, Christopher K. W., Bourassa, Mark Allan, Morey, Steven L., Florida State University, College of Arts and Sciences,...
Show moreChen, Xu, Dewar, William K., Chassignet, Eric P., Tam, Christopher K. W., Bourassa, Mark Allan, Morey, Steven L., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: An accurate representation of air-sea interaction is crucial to the accurate numerical prediction of ocean, weather, and climate. It is known that sea surface temperature (SST) gradients and surface currents in the oceanic mesoscale regime significantly affect air-sea fluxes of momentum and heat, and the mesoscale-modified air-sea fluxes also influence the ocean dynamics on various scales. Previous studies found that resolving the mutual feedbacks between mesoscale processes and the...
Show moreAn accurate representation of air-sea interaction is crucial to the accurate numerical prediction of ocean, weather, and climate. It is known that sea surface temperature (SST) gradients and surface currents in the oceanic mesoscale regime significantly affect air-sea fluxes of momentum and heat, and the mesoscale-modified air-sea fluxes also influence the ocean dynamics on various scales. Previous studies found that resolving the mutual feedbacks between mesoscale processes and the atmosphere improved the accuracy of modeling for ocean, weather, and climate. In the submesoscale regime recently revealed by high-resolution numerical models and observations, the SST gradient and surface currents are found to be much stronger than those in the mesoscale. However, the mutual feedbacks between the submesoscale processes and the atmosphere are not well understood. To quantitatively assess the mutual responses between the air-sea fluxes and the submesoscale processes, a non-hydrostatic ocean model coupled with an atmospheric boundary layer module is implemented making it possible to examine the air-sea interactions over submesoscale regime. We here argue that the inclusion of surface currents in air-sea bulk flux parameterization and the atmospheric thermodynamic adjustments to the ocean surface are determined to be significant for modeling accurate wind stress and air-sea turbulent heat fluxes in the submesoscale regime. The results show that the linear relationship between wind stress curl/divergence and crosswind/downwind SST gradient, revealed in the mesoscale regime, do not exist in the submesoscale regime. Additionally, the magnitudes of positive and negative wind stress curl introduced by submesoscale processes are much greater than the magnitude of wind stress curl introduced by mesoscale processes. This study also finds that the evolution of submesoscale processes is closely associated with the potential vorticity (PV) budget. Because different fields of wind stress and turbulent heat fluxes are introduced by the influence of submesoscale surface velocity field and/or temperature field, these wind stress and heat flux fields can interact with submesoscale surface structures and provide different PV injections into the ocean. Therefore, the evolution of submesoscale processes is significantly influenced by the submesoscale-modified air-sea fluxes. This study serves as a starting point in the investigation of the two-way feedback between the atmosphere and oceanic submesoscale processes. It shows that numerically resolving the two-way air-sea coupling in the submesoscale regime significantly changes air-sea flux and the oceanic submesoscale dynamics.
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Date Issued: 2018
Identifier: 2018_Fall_Chen_fsu_0071E_14913
Format: Thesis

Title: Barrier Layer Development Local to Tropical Cyclones.
Creator: Steffen, John, Bourassa, Mark Allan, Elsner, James B., Hart, Robert E. (Robert Edward), Chagnon, Jeffrey M., Clarke, Allan J., Florida State University, College of Arts and...
Show moreSteffen, John, Bourassa, Mark Allan, Elsner, James B., Hart, Robert E. (Robert Edward), Chagnon, Jeffrey M., Clarke, Allan J., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: The objective of this study is to quantify barrier layer development due to tropical cyclone (TC) passage using Argo float observations of temperature and salinity. To accomplish this objective, a climatology of Argo float measurements is developed from 2001-2014 for the Atlantic, eastern Pacific, and central Pacific basins. Each Argo float sample consists of a pre-storm and post-storm temperature and salinity profile pair. In addition, a no-TC Argo pair dataset is derived for comparison to...
Show moreThe objective of this study is to quantify barrier layer development due to tropical cyclone (TC) passage using Argo float observations of temperature and salinity. To accomplish this objective, a climatology of Argo float measurements is developed from 2001-2014 for the Atlantic, eastern Pacific, and central Pacific basins. Each Argo float sample consists of a pre-storm and post-storm temperature and salinity profile pair. In addition, a no-TC Argo pair dataset is derived for comparison to account for natural ocean state variability and instrument sensitivity. The Atlantic basin shows a statistically significant increase in post-TC barrier layer thickness (BLT) and barrier layer potential energy (BLPE) that is largely attributable to an increase of 2.6 m in the post-TC isothermal layer depth (ITLD). The eastern Pacific basin shows no significant changes to any barrier layer characteristic, likely due to a shallow and highly stratified pycnocline. However, the near-surface layer freshens in the upper 30 m after TC passage, which increases static stability. Finally, the central Pacific has a statistically significant freshening in the upper 20-30 m that increases upper-ocean stratification by ~35%. The mechanisms responsible for increases in BLPE vary between the Atlantic and both Pacific basins; the Atlantic is sensitive to ITLD deepening, while the Pacific basins show near-surface freshening to be more important in barrier layer development. In addition, Argo data subsets are used to investigate the physical relationships between the barrier layer and TC intensity, TC translation speed, radial distance from TC center, and time after TC passage. ROMS model hindcasts of Hurricange Gonzalo (2014) characterize the upper-ocean response to TC precipitation forcing. Several different vertical mixing parameterizations are tested to determine their sensitivity to precipitation. For all mixing schemes, TC precipitation accounts for ocean surface freshening of about 0.3 PSU. The dominant terms in the near-surface salinity budget are the total advection and vertical diffusivity. The influence of precipitation-induced changes to the SST response is more complicated. In some areas, increased upper-ocean stratification mutes the SST cooling response. However, in other areas, cooling can be stronger when precipitation is prescribed. Dynamical changes in upper-ocean currents and the curl of the surface stress can induce a stronger cooling response in these regions.
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Date Issued: 2018
Identifier: 2019_Spring_Steffen_fsu_0071E_14955
Format: Thesis

Title: Dynamics-Guided Analysis of Tropical Waves.
Creator: Sun, Jie, Wu, Zhaohua, She, Yiyuan, Bourassa, Mark Allan, Cai, Ming, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreSun, Jie, Wu, Zhaohua, She, Yiyuan, Bourassa, Mark Allan, Cai, Ming, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Tropical waves are important tropical and global weather/climate systems as well as carriers for redistributing global energy. For decades, a multitude of tropical wave theories that attempt to explain the origins and maintenance mechanisms of tropical waves and the interactions between them and other tropical systems have been put forth by scientists. Partly due to the lack of effective analysis tools, observational studies of tropical waves have not been comprehensive enough, leaving many...
Show moreTropical waves are important tropical and global weather/climate systems as well as carriers for redistributing global energy. For decades, a multitude of tropical wave theories that attempt to explain the origins and maintenance mechanisms of tropical waves and the interactions between them and other tropical systems have been put forth by scientists. Partly due to the lack of effective analysis tools, observational studies of tropical waves have not been comprehensive enough, leaving many of the proposed theories unverified. For example, Fourier spectrum analysis based methods can hardly be used to obtain the accurate climatology of tropical waves because of the impacts of locality. This study serves two purposes: (1) To introduce and develop novel dynamics-based effective methods and to tailor them for isolating spatiotemporally local tropical waves of different spatiotemporal scales; and (2) To shed new insights into the climatological features of tropical waves, such as life cycles, their interactions with other tropical phenomena, and their dynamical implications. To accomplish the first goal, we introduce the multi-dimensional ensemble mode decomposition (MEEMD) method to decompose different meteorological variables. This method is combined with our newly developed optimization methods based on tropical wave theory in this study to form a dynamics based tropical wave diagnosis package. The capability of the new package is validated using both synthetic data and observational data. It is demonstrated that our package has high capability of separating tropical waves of different spatiotemporal scales as well as of different types. With the readiness of the above package, we systematically analyzed characteristic of tropical waves of different types, with emphases being placed on the spatiotemporal structures and their life cycle. It is revealed that all types of tropical waves have significantly different climatological characteristics, from wavenumbers and wave frequencies to their propagating properties. It is revealed that that upper and lower tropospheric tropical waves have distinguishable dynamic characteristics, too different for researchers to adopt a first baroclinic mode structure in the vertical to understand the origin and destiny of various tropical waves. We also quantify the modulation characteristics of high frequency tropical waves by intraseasonal oscillations.
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Date Issued: 2017
Identifier: FSU_FALL2017_Sun_fsu_0071E_14169
Format: Thesis

Title: The Impact of Tropical Cyclones on Upper Atmospheric Chemistry Using a High-Resolution Chemical Transport Model and Aircraft Observations.
Creator: Preston, Aaron David, Fuelberg, Henry E., Van Winkle, David H., Barth, Mary, Hart, Robert E. (Robert Edward), Sura, Philip, Liu, Guosheng, Florida State University, College of...
Show morePreston, Aaron David, Fuelberg, Henry E., Van Winkle, David H., Barth, Mary, Hart, Robert E. (Robert Edward), Sura, Philip, Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: This research focuses on the transport of chemical species to the upper troposphere/lower stratosphere (UTLS) by tropical cyclones (TCs). Species such as carbon monoxide, nitrogen oxides, and ozone have been found to exert a greater influence on climate change at these high altitudes than if remaining near the surface. Typhoon Mireille (1991) is examined in the western North Pacific (WNP) Ocean basin using in situ aircraft-derived chemical data from NASA's Pacific Exploratory Mission-West A...
Show moreThis research focuses on the transport of chemical species to the upper troposphere/lower stratosphere (UTLS) by tropical cyclones (TCs). Species such as carbon monoxide, nitrogen oxides, and ozone have been found to exert a greater influence on climate change at these high altitudes than if remaining near the surface. Typhoon Mireille (1991) is examined in the western North Pacific (WNP) Ocean basin using in situ aircraft-derived chemical data from NASA's Pacific Exploratory Mission-West A field project. The Weather Research and Forecasting (WRF) model was used with chemistry (WRF-Chem) at an innermost grid spacing of 3 km to explicitly resolve the convection being studied. Results show that pollution from distant sources is ingested by Mireille and subsequently lofted by eyewall convection to the UTLS, enhancing concentrations in this region. Flux calculations suggest that a strong TC, such as Mireille, can impact UTLS chemistry as much as a continental middle latitude cyclone. Furthermore, overshooting cells in Mireille produced chemical flux density values at the tropopause level as much as 10-20 times greater than that of the TC as a whole. Thus, although the overshooting tops comprise only a small area of the total TC, they transport large quantities of gaseous species to the UTLS because of their very strong updrafts. Results also suggest that millions of cars and/or several power plants would need to be hypothetically placed in the upper troposphere to have the same impact on chemical concentrations as Mireille. This demonstrates the transport strength of the TC as a whole. Improved understanding of atmospheric chemistry in the WNP basin is important, especially in the context of increasing Asian emissions and a changing climate. Furthermore, since it has been hypothesized that global warming will lead to more intense storms, it is important to understand TCs’ role in chemical transport.
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Date Issued: 2017
Identifier: FSU_FALL2017_Preston_fsu_0071E_14129
Format: Thesis

Title: Coupling Ocean Currents and Waves with Wind Stress over the Gulf Stream.
Creator: Shi, Qi, Bourassa, Mark Allan, Yuan, Xin, Dewar, William K., Chagnon, Jeffery M., Holmes, Christopher D., Florida State University, College of Arts and Sciences, Department of...
Show moreShi, Qi, Bourassa, Mark Allan, Yuan, Xin, Dewar, William K., Chagnon, Jeffery M., Holmes, Christopher D., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The exchange of momentum, heat, moisture, and gas across the air-sea interface plays a crucial role in atmospheric and oceanic circulations on variety of spatial and temporal scales. That is why improved understanding and realistic simulations of air-sea flux are critical to advancing oceanic and atmospheric prediction capabilities. This study provides the first detailed analysis of oceanic and atmospheric responses to the current-stress, wave-stress, and wave-current-stress interaction at...
Show moreThe exchange of momentum, heat, moisture, and gas across the air-sea interface plays a crucial role in atmospheric and oceanic circulations on variety of spatial and temporal scales. That is why improved understanding and realistic simulations of air-sea flux are critical to advancing oceanic and atmospheric prediction capabilities. This study provides the first detailed analysis of oceanic and atmospheric responses to the current-stress, wave-stress, and wave-current-stress interaction at the Gulf Stream using a high-resolution three-way coupled regional modeling system. This modeling system allows for the exchange of data fields between the atmospheric model—Weather Research and Forecasting (WRF), the ocean model—Regional Ocean Modeling System (ROMS), and the wave model—Simulating Waves Nearshore (SWAN) through the Model Coupling Toolkit (MCT). We perform four one-month simulations for October 2012, a time period when the impact of wind and waves is relatively large. The four experiments differ in how wind shear and surface roughness length are calculated in the bulk flux parameterization: 1) The control experiment calculates the surface roughness length by using the surface wind only (no shear from currents). 2) The current experiment interactively takes into account surface currents in the wind shear. 3) The wave experiment explicitly includes the sea-state parameters in calculating the roughness length. 4) The current-wave experiment computes the surface roughness by taking into account the current-induced shear and sea state simultaneously. In general, our results highlight the substantial impact of coupling currents/waves with wind stress on the air-sea flux exchange and ocean upwelling over the Gulf Stream. Two-way coupling of waves and wind stress causes wind stress (30-day averaged) increase up to 12% in 95th percentile of the model domain, and increases greater than 5% are found in 50% of the model domain. For two-way coupling of surface currents and wind stress, both positive and negative changes in wind stress (greater than 5%) are found at the Gulf Stream, with only small changes elsewhere. The pattern of wind stress change in the wave-current-stress coupling experiment is similar to that in the current-stress coupling experiment, with over 15% increase of wind stress at the Gulf Stream. The current impact on wind stress cancels out the wave impact outside of the Gulf Stream in the wave-current-stress experiment. Coupling currents/waves with wind stress also change the wind stress curl, which impacts the response patterns of upwelling and downwelling in the upper ocean. Changes in wind stress and its curl due to coupling processes lead to changes in SST and ocean current in the Gulf Stream. Considerable SST change (in excess of 1 oC) and ocean current change (in excess of 0.2 m/s) are collocated near the SST front region in the shape of warm/cold core eddies in all coupling configurations. We perform a mixed layer heat budget analysis to investigate the physical processes happening in the ocean mixed layer and their contribution to the SST changes. Substantial latent heat flux changes exceeding 20 W/m2 and sensible heat flux changes exceeding 5 W/m2 are found over the Gulf Stream in all coupled configurations. Sensitivity test shows that SST-induced differences of air-sea temperature and humidity are major contributors to the LHF and SEN changes. The coupling processes also change the surface wind convergence, which further impacts precipitation.
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Date Issued: 2017
Identifier: FSU_FALL2017_Shi_fsu_0071E_14148
Format: Thesis

Title: Using Radar-Derived Parameters to Develop Probabilistic Guidance for Lightning Cessation within Isolated Convection near Cape Canaveral, Florida.
Creator: Patton, Joseph Ray, Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Chagnon, Jeffery M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean,...
Show morePatton, Joseph Ray, Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Chagnon, Jeffery M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Almost daily summer time thunderstorms in central Florida frequently halt outdoor operations, requiring that one wait some prescribed time after an observed lightning flash to safely resume activities. This is an especially important problem for the U.S. Air Force’s 45th Weather Squadron (45WS). Prior research suggests that these wait times might be safely shortened by observing reflectivity values and hydrometeor type with radar to safely predict that lightning has ended for a particular...
Show moreAlmost daily summer time thunderstorms in central Florida frequently halt outdoor operations, requiring that one wait some prescribed time after an observed lightning flash to safely resume activities. This is an especially important problem for the U.S. Air Force’s 45th Weather Squadron (45WS). Prior research suggests that these wait times might be safely shortened by observing reflectivity values and hydrometeor type with radar to safely predict that lightning has ended for a particular isolated thunderstorm. The main goal of this study was to create a usable operational tool that would create probabilistic guidance for the 45WS to use for determining total lightning cessation for isolated storms. The study analyzed dual-polarized radar data from isolated thunderstorms to develop probabilistic lightning cessation guidance for the 45WS. We tracked 184 isolated storms in central Florida at 1 min intervals using radar and lightning detection systems including radar reflectivity and hydrometeor classification at isothermal levels. For each isolated storm we investigated its maximum reflectivity and graupel presence at the 0, -5, -10, -15, and -20°C levels and composite (maximum) reflectivity. A random sample of all the 1 min interval data was used to train a generalized linear model (GLM) to make a probabilistic prediction that cessation had occurred. The GLM revealed that the most statistically significant predictors for lightning cessation were maximum reflectivity at the composite and 0 °C levels along with graupel presence at the -5, -10, -15, and -20°C levels. The GLM was trained with 1000 random samples of minutes to bootstrap the results, with the median values of the final set of predictor coefficients used to calculate probabilities that cessation had occurred at that minute. Forecast verification statistics from another random sample of tracked minutes then were used to analyze the performance of the GLM with different probability thresholds (95.0%, 97.5%, and 99.0%) for determining lightning cessation. Applying this cessation guidance from our GLM as though the storms were occurring in real time revealed that only about 1% of the 184 storms in our data set had observed lightning after the GLM suggested cessation had already occurred, an event which would threaten life and property. Even the median of the most conservative probability threshold (99.0%) improved on the guidance currently being used by the 45WS, while the 95.0% probability guidance had a median wait time of just 9 min after cessation.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Patton_fsu_0071N_14100
Format: Thesis

Title: Evaluation of a Bispectral Fog Detection Technique with a Low Earth Orbiting Satellite for Fog Events in Florida.
Creator: Swearingen, Aaron, Ray, Peter S., Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Misra, Vasubandhu, Florida State University, College of Arts and Sciences,...
Show moreSwearingen, Aaron, Ray, Peter S., Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: According to the United States Department of Transportation (US DOT), an average of over 28,000 crashes and almost 500 deaths annually occurred as a result of fog-related vehicular accidents. In Florida, the January 2008 and January 2012 fog-related multi-car accidents claimed the lives of four and eleven people, respectively. A more effective fog warning system could include the use of remote sensing. The ground observation sites used to detect fog statewide are both widely and unevenly...
Show moreAccording to the United States Department of Transportation (US DOT), an average of over 28,000 crashes and almost 500 deaths annually occurred as a result of fog-related vehicular accidents. In Florida, the January 2008 and January 2012 fog-related multi-car accidents claimed the lives of four and eleven people, respectively. A more effective fog warning system could include the use of remote sensing. The ground observation sites used to detect fog statewide are both widely and unevenly dispersed. Many high-traffic areas affected by fog are not monitored by ground equipment, leading to poor forecasting and detection of fog in these areas. A combination of both ground observations and remote sensing may lead to better statewide fog detection and forecasting. A bispectral nighttime fog detection technique is used to determine the presence of fog across the state of Florida. This technique uses brightness temperature differences (BTD) between two infrared (IR) channels. The performance of the technique is validated through the use of six months of observation data from AWOS/ASOS sites across the state. An optimum fog detection threshold is found based on the BTD values. Both the optimum threshold and the skill of the optimum threshold are compared to a previous study which used a geostationary satellite for fog detection. The bispectral technique shows little skill, with a large amount of misses and false detections of fog. The low skill can be attributed to the fact that MODIS makes only one nighttime pass which may not necessarily be when fog has formed. The increased spatial resolution of the MODIS sensor over the previous generation GOES Imager does not make up for the decreased number of nighttime satellite passes in a given day.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Swearingen_fsu_0071N_14009
Format: Thesis

Title: An Examination of El Niño and La Niña Teleconnections to Sahel and Guinea Coast Rainfall in the Context of the 1968 Rainfall Regime Change.
Creator: Vaughan, Thomas Ashley, Nicholson, Sharon E., Sura, Philip, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts and...
Show moreVaughan, Thomas Ashley, Nicholson, Sharon E., Sura, Philip, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The Sahel and Guinea Coast regions of Africa have long been the subject of studies on interannual and intraseasonal rainfall variability. The unique geography, monsoon circulation regime, and a variety of climatic teleconnections produce large variations in year-to-year rainfall across the region. These large fluctuations in rainfall can have devastating effects on the inhabitants of West Africa, who rely on the rainfall for both agriculture and human consumption. Thus, a better understanding...
Show moreThe Sahel and Guinea Coast regions of Africa have long been the subject of studies on interannual and intraseasonal rainfall variability. The unique geography, monsoon circulation regime, and a variety of climatic teleconnections produce large variations in year-to-year rainfall across the region. These large fluctuations in rainfall can have devastating effects on the inhabitants of West Africa, who rely on the rainfall for both agriculture and human consumption. Thus, a better understanding of the nature of rainfall variability in the area is warranted. The El Niño/Southern Oscillation (ENSO), one of the most studied climate phenomena, is known to have far-reaching impacts on weather across the globe. This study provides one of the most comprehensive and complete analyses of the relationship between ENSO and rainfall across the Sahel and Guinea Coast to date. Several previous studies have found little connection between Sahel rainfall and ENSO phase, while others have suggested that ENSO can result in changes within the monsoon circulation and cause a reduction in Sahel rainfall during El Niño years. By utilizing the largest and longest dataset of rainfall gauge data available, this study provides an analysis of rainfall anomalies experienced during El Niño and La Niña years from 1921-2012 in the context of a major shift in the rainfall regime that occurred around the year 1968. This research finds that before 1968, rainfall during the peak Sahel rainy season in El Niño years was below normal, but above normal in the Guinea Coast. The same is observed after 1968, but the anomalies are of stronger magnitude than before 1968, suggesting an increased ENSO-Sahel rainfall teleconnection after 1968. Similar intensifications of the El Niño signal are observed in other seasons as well. In general, opposite rainfall anomalies were observed during La Niña years when compared to El Niño years. An increase in La Niña influence in more recent years is also detected. An analysis of the consistency of the ENSO signal suggests that the ENSO rainfall response is most consistent in areas of the Sahel during the JAS (-1), OND (-1), JAS, and OND seasons. Evidence also suggests that there was a weakening of the Sahel/Guinea Coast dipole after 1968. Finally, an analysis of upper air circulations shows few differences in zonal winds during El Niño and La Niña years versus non-ENSO years, suggesting the relationship between ENSO and Sahel rainfall may be fairly weak. There are some subtle differences seen, however, when comparing years before 1968 to years afterwards that were consistent with the observed rainfall anomalies in certain seasons. This study concludes that the rainfall response to El Niño and La Niña events in the Sahel and Guinea Coast as a whole is relatively inconsistent, but there was some meaningful connection found between ENSO and rainfall in the Sahel during certain seasons outlined above. This relationship intensified after the 1968 rainfall regime change, consistent with findings from previous studies.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Vaughan_fsu_0071N_14087
Format: Thesis

Title: The Influence of Cloud Microphysical Schemes on Simulated Convection over the Cape Canaveral Region in South Easterly Flow.
Creator: Dawson, Matthew G., Chagnon, Jeffery M., Hart, Robert E. (Robert Edward), Fuelberg, Henry E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean,...
Show moreDawson, Matthew G., Chagnon, Jeffery M., Hart, Robert E. (Robert Edward), Fuelberg, Henry E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Simulations are conducted using the Weather Research and Forecasting (WRF) model in a nested domain having horizontal grid lengths of 12 km, 4 km, and 1.33km, in order to establish the dynamic and thermodynamic controls that three popular cloud Micro Physics (MP) schemes exert over the sea-breeze-forced convection commonly seen over the Cape Canaveral region. Experiments focus on a period from 12-20 Aug 2016 in a regime dominated by high pressure and southeasterly flow; simulations were...
Show moreSimulations are conducted using the Weather Research and Forecasting (WRF) model in a nested domain having horizontal grid lengths of 12 km, 4 km, and 1.33km, in order to establish the dynamic and thermodynamic controls that three popular cloud Micro Physics (MP) schemes exert over the sea-breeze-forced convection commonly seen over the Cape Canaveral region. Experiments focus on a period from 12-20 Aug 2016 in a regime dominated by high pressure and southeasterly flow; simulations were initialized at 06Z on each day during the week and run for a period of 24 hours. One double-moment and two single-moment MP schemes were employed in the simulations for comparison. Results demonstrate that the MP scheme can have a substantial influence on regional convective simulations - large enough to shift the trigger and location of convection. Large differences in domain averaged bulk hydrometeor quantities are found, particularly in the vertical profile of the rain bulk mixing ratio. Simulations employing the double moment scheme systematically underestimate the total precipitation throughout each day but also systematically produced stronger cold pools. Plots of vertical cloud water and potential temperature indicate a greater concentration of cloud droplets at an elevation of 2-4 km and a much larger latent heating when the double moment scheme was used. Modulation of the latent heat release within the double moment scheme is hypothesized to occur from the Drop Size Distribution (DSD), and the prescribed Cloud Condensation Nuclei CCN parameter used to calculate this distribution.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Dawson_fsu_0071N_13916
Format: Thesis

Title: On the Obscured Relationship between Size and Intensity of Tropical Cyclones: A Preliminary Study.
Creator: Hathaway, Nikki Marie, Cai, Ming, Hart, Robert E. (Robert Edward), Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts...
Show moreHathaway, Nikki Marie, Cai, Ming, Hart, Robert E. (Robert Edward), Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Both intuition and previous statistical analysis suggests that in general, hurricane size tends to increase with intensity. However, such statistical correlation, including the statistical significance and even the sign of the correlation, between hurricane size and intensity strongly depends on the sample hurricanes in the data pool for the correlation analysis. For example, there are ample instances when a hurricane at different times can have a similar size but differ in terms of intensity...
Show moreBoth intuition and previous statistical analysis suggests that in general, hurricane size tends to increase with intensity. However, such statistical correlation, including the statistical significance and even the sign of the correlation, between hurricane size and intensity strongly depends on the sample hurricanes in the data pool for the correlation analysis. For example, there are ample instances when a hurricane at different times can have a similar size but differ in terms of intensity and vice versa. Therefore, predictions based on intuition or statistics often fail when considering an individual hurricane. In this thesis research, we attempt to apply a theoretical model in conjunction with observational case studies to gain insight on the main factors that make the relationship between both hurricane size and intensity, obscured. This theoretical model will apply an analytical analysis of the inertial instability neutral radial profile of an isolated gradient-wind balanced circular vortex in an f-plane shallow water equation model, which shows that the relationship between the size and the maximum tangential wind speed is not unique, because the size also depends on the radius of maximum wind. The radial profile of wind under neutral conditions of inertial instability reveals that hurricane size and intensity can have either a positive, near-zero, or negative correlation depending on the sample of hurricanes in the dataset from which such correlation is obtained. The main conclusion derived from the theoretical model is that the relationship between hurricane size and intensity can be obscured due to only one specific factor (i.e., the radius of maximum wind) that also influences the size. The theoretical model also predicts that the latitudinal position only weakly obscures the relationship, as long as the hurricane is not too close to the equator. We have examined whether the size inferred from the radial profile of inertially neutral wind would be able to capture its observational counterparts. Specifically, we examined five selected hurricanes derived from the Extended Best Track (EBT) Data, namely Katrina (2005), Ike (2008), Gustav (2008), Sandy (2012), and Joaquin (2015). We have performed a correlation analysis on the observed size and the size predicted by the simple theoretical model by using the information of maximum wind speed and its radius of each of the five hurricanes throughout the phases of each tropical cyclone’s (TC) life cycle. We found that the size obtained from the barotropic inertially neutral radial profile underestimates the size of observed hurricane by a factor of 2-2.5. This suggests that the observed hurricane wind’s radial profile does not follow angular momentum conservation or an air parcel would lose angular momentum as it converges towards the eyewall, mainly due to surface drag and eddy-mixing processes. This finding also implies that there are other parameters besides these three factors (intensity, radius of maximum wind, and latitude) that influence an individual hurricane size. This implies that the relationship between size and intensity is more complex than that predicted by the simple theoretical model. Our analysis suggests that about 1/3 (48 out of 174) of the observed cases show that other factors may strongly affect hurricane size. By removing these 48 data points that are indicative of possible strong impacts from the external factors, the R-squared value of the linear regression line between the observed size and the size predicted by the theoretical model increases substantially (from R2 = 46.3% to 71.5% on average). The inspection of the timing and location of these “external” data points indicate that they often occur in situations when (i) encountering big islands or land mass (e.g., Cuba for Ike) and (ii) undergo a very rapid weakening/intensifying transition (Joaquin). Therefore, the size information predicted by the simple theoretical model does capture the size record for most the track records (126 out of 174), suggesting that the most important factors that influence hurricane size are both maximum wind speed and the radius of maximum wind speed.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Hathaway_fsu_0071N_13990
Format: Thesis

Title: The Influence of Helicity on Regulating Diabatic Potential Vorticity in Isolated Convective Storms.
Creator: Jo, Enoch, Chagnon, Jeffery M., Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreJo, Enoch, Chagnon, Jeffery M., Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Severe supercell thunderstorms exhibit rotation which aids in organization and maintenance of the storms. The effects of helicity and diabatic heating on the structure of potential vorticity (PV) in a supercell thunderstorm is examined through simple theoretical analysis using the linearized form of the Boussinesq system of equations and using sensitivity experiments in the Weather Research and Forecasting (WRF) model. The linear analysis shows that in the presence of helicity, a region of...
Show moreSevere supercell thunderstorms exhibit rotation which aids in organization and maintenance of the storms. The effects of helicity and diabatic heating on the structure of potential vorticity (PV) in a supercell thunderstorm is examined through simple theoretical analysis using the linearized form of the Boussinesq system of equations and using sensitivity experiments in the Weather Research and Forecasting (WRF) model. The linear analysis shows that in the presence of helicity, a region of diabatic heating will favor one PV pole, resulting in storm rotation. In an environment with no helicity, a PV dipole will straddle the region of diabatic heating. The amplitude of the diabatically generated PV is regulated by the ratio H/U^2 where H is the helicity and U is the component of wind directed parallel to the background horizontal vorticity. This theoretical analysis of PV informs the design of five different idealized WRF experiments which demonstrate the role of helicity and latent heating in storm organization under differing environmental wind conditions. The WRF sensitivity tests confirm that a larger (smaller) H/U^2 results in more (less) storm rotation. This thesis offers a new PV perspective on the origin of storm scale rotation in convective environments and highlights the role of microphysical processes and latent heating in storm rotation.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Jo_fsu_0071N_14088
Format: Thesis

Title: The Role of Equatorial Pacific Currents in El Nino and El Nino Prediction.
Creator: Zhang, Xiaolin, Clarke, Allan J., Tam, Christopher K. W., Bourassa, Mark Allan, Dewar, William K., Landing, William M., Florida State University, College of Arts and Sciences,...
Show moreZhang, Xiaolin, Clarke, Allan J., Tam, Christopher K. W., Bourassa, Mark Allan, Dewar, William K., Landing, William M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Fundamental to an understanding of El Niño/Southern Oscillation climate fluctuations is an understanding of the interannual equatorial Pacific surface flows, which advect the surface waters and change the sea surface temperature. While some knowledge of the observed interannual flows has already been obtained, some key features are still not fully understood. Using the long records of satellite altimeter data, together with long in situ records of current, salinity and temperature from the...
Show moreFundamental to an understanding of El Niño/Southern Oscillation climate fluctuations is an understanding of the interannual equatorial Pacific surface flows, which advect the surface waters and change the sea surface temperature. While some knowledge of the observed interannual flows has already been obtained, some key features are still not fully understood. Using the long records of satellite altimeter data, together with long in situ records of current, salinity and temperature from the TAO/TRITON array in the equatorial Pacific, the observed interannual surface flows, their dynamics and link to the El Niño Prediction can be understood better. In the first half of the thesis, I used theoretical arguments and a wind-forced ocean model to understand why the equatorial eastern Pacific flow leads sea level, eastern equatorial thermocline displacement and El Niño indices. This half of the thesis is based on the result that for large zonal scales and low frequencies, wind-forced sea level, even near the equator, can be described by wind-forced long Rossby waves. In the eastern equatorial Pacific where the interannual wind forcing is small, these waves are essentially locally unforced and propagate westward from the boundary. At the boundary the wave’s sea level is in phase because of geostrophy and no normal flow to the boundary. However, because the waves propagate more slowly with increasing latitude, west of the boundary lag increases as latitude increases. Consequently a northward sea level gradient is like a time derivative, and the zonal geostrophic flow is like a time derivative of the sea level. This implies that the equatorial flow should lead the equatorial sea level by about 9 months on El Niño time scales. Analysis shows that when dissipation of the large-scale flow is taken into account, this lead is reduced to about 3 months. This lead time is approximately the dissipation time scale of the second vertical mode, which dominates the zonal surface flow. Since the eastern equatorial Pacific sea level is proportional to eastern equatorial thermocline displacement and El Niño, the zonal equatorial flow leads El Niño indices. Analysis further shows that the zonally-averaged equatorial Pacific sea level leads El Niño, and that this lead is associated with the geostrophic zonal velocity and the long Rossby wave physics in the eastern equatorial Pacific. The second part of this work addresses the influence of the heavy precipitation on the Western equatorial Pacific Ocean. Surface and subsurface salinity and temperature measurements at 137oE, 147oE, and 156oE since the late 1990s from the western equatorial Pacific TRITON moored array indicate that the large interannual sea surface salinity (SSS) fluctuations there change little with depth over the top 50 m of the water column. Beneath this surface layer the SSS signal decreases, and is usually much smaller at about 100 m depth. The isothermal layer depth (ILD) ranges from about 50–70 m and estimates of dynamic height relative to the ILD indicate a near-surface salinity-driven contribution to the monthly sea level anomaly that is uncorrelated with, and smaller than, interannual sea surface height (SSH) estimated from altimeter data. Despite the smaller size of , its meridional gradient dominates the total sea level meridional gradient and thus the corresponding shallow equatorially-trapped interannual fresh water jet dominates the near-surface zonal interannual flow. This jet-like flow has a meridional scale of only about 2–3o of latitude, an amplitude of 23cm/s, and is associated with the zonal back and forth displacement of the western equatorial warm/fresh pool that is fundamental to El Niño. The jet is not forced by the interannual fresh water surface flux but rather by wind stress anomalies that are mostly east of the warm/fresh pool edge during La Niña and mostly west of it during El Niño.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Zhang_fsu_0071E_13691
Format: Thesis

Title: Case-Base Devaluation of a Physical Initialization Technique for Assimilating Precipitation in NWP.
Creator: Chaney, Kirsten Maria, Chagnon, Jeffery M., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Ross, Robert S., Florida State University, College of Arts and Sciences,...
Show moreChaney, Kirsten Maria, Chagnon, Jeffery M., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Ross, Robert S., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: A novel method for assimilating precipitation observations into a numerical weather prediction model is presented and evaluated for a case study of a monsoon rainfall event over the Asian subcontinent. The method, known as physical initialization (Krishnamurti et al. 1991), involves the iterative adjustment of the vertical moisture profile towards a configuration that would permit simulated precipitation where there is observed precipitation. The physical initialization procedure was...
Show moreA novel method for assimilating precipitation observations into a numerical weather prediction model is presented and evaluated for a case study of a monsoon rainfall event over the Asian subcontinent. The method, known as physical initialization (Krishnamurti et al. 1991), involves the iterative adjustment of the vertical moisture profile towards a configuration that would permit simulated precipitation where there is observed precipitation. The physical initialization procedure was incorporated into the Weather Research and Forecasting (WRF) model. Evaluation of the technique was accomplished through the comparison of two simulations: one with the physical initialization and one without. Both simulations were evaluated against TRMM rainfall. The impact of physical initialization was shown to be beneficial to the two-day typical Indian Summer Monsoon case study with respect to the rainfall forecast skill as well as the mesoscale circulation and vertical redistribution of moisture. Specifically, the correlation between simulated and observed 3-hour accumulated precipitation is higher throughout the two-day forecast period in the run with physical initialization. The probability distribution of rainfall amounts in the run with physical initialization was also more similar to the observations, whereas the control WRF run exhibited a large bias of widespread light to moderate rain. Additionally, the run with physical initialization improves the forecast location of mesoscale precipitation features and removes regions of spurious rain from the forecast. Simulations were conducted and evaluated for this case only.
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Date Issued: 2017
Identifier: FSU_SUMMER2017_Chaney_fsu_0071N_14094
Format: Thesis

Title: Improving Satellite-Based Snowfall Estimation: A New Method for Classifying Precipitation Phase and Estimating Snowfall Rate.
Creator: Sims, Elizabeth M., Liu, Guosheng, Meyer-Baese, Anke, Bourassa, Mark Allan, Cai, Ming, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth,...
Show moreSims, Elizabeth M., Liu, Guosheng, Meyer-Baese, Anke, Bourassa, Mark Allan, Cai, Ming, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: In order to study the impact of climate change on the Earth's hydrologic cycle, global information about snowfall is needed. To achieve global measurements of snowfall over both land and ocean, satellites are necessary. While satellites provide the best option for making measurements on a global scale, the task of estimating snowfall rate from these measurements is a complex problem. Satellite-based radar, for example, measures effective radar reflectivity, Ze, which can be converted to...
Show moreIn order to study the impact of climate change on the Earth's hydrologic cycle, global information about snowfall is needed. To achieve global measurements of snowfall over both land and ocean, satellites are necessary. While satellites provide the best option for making measurements on a global scale, the task of estimating snowfall rate from these measurements is a complex problem. Satellite-based radar, for example, measures effective radar reflectivity, Ze, which can be converted to snowfall rate, S, via a Ze-S relation. Choosing the appropriate Ze-S relation to apply is a complicated problem, however, because quantities such as particle shape, size distribution, and terminal velocity are often unknown, and these quantities directly affect the Ze-S relation. Additionally, it is important to correctly classify the phase of precipitation. A misclassification can result in order-of-magnitude errors in the estimated precipitation rate. Using global ground-based observations over multiple years, the influence of different geophysical parameters on precipitation phase is investigated, with the goal of obtaining an improved method for determining precipitation phase. The parameters studied are near-surface air temperature, atmospheric moisture, low-level vertical temperature lapse rate, surface skin temperature, surface pressure, and land cover type. To combine the effects of temperature and moisture, wet-bulb temperature, instead of air temperature, is used as a key parameter for separating solid and liquid precipitation. Results show that in addition to wet-bulb temperature, vertical temperature lapse rate also affects the precipitation phase. For example, at a near-surface wet-bulb temperature of 0°C, a lapse rate of 6°C km-1 results in an 86 percent conditional probability of solid precipitation, while a lapse rate of -2°C km-1 results in a 45 percent probability. For near-surface wet-bulb temperatures less than 0°C, skin temperature affects precipitation phase, although the effect appears to be minor. Results also show that surface pressure appears to influence precipitation phase in some cases, however, this dependence is not clear on a global scale. Land cover type does not appear to affect precipitation phase. Based on these findings, a parameterization scheme has been developed that accepts available meteorological data as input, and returns the conditional probability of solid precipitation. Ze-S relations for various particle shapes, size distributions, and terminal velocities have been developed as part of this research. These Ze-S relations have been applied to radar reflectivity data from the CloudSat Cloud Profiling Radar to calculate the annual mean snowfall rate. The calculated snowfall rates are then compared to surface observations of snowfall. An effort to determine which particle shape best represents the type of snow falling in various locations across the United States has been made. An optimized Ze-S relation has been developed, which combines multiple Ze-S relations in order to minimize error when compared to the surface snowfall observations. Additionally, the resulting surface snowfall rate is compared with the CloudSat standard product for snowfall rate.
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Date Issued: 2017
Identifier: FSU_2017SP_Sims_fsu_0071E_13720
Format: Thesis

Title: Predictability and Dynamics of the Genoa Low: Case Study and Operational Considerations.
Creator: Snyder, Michael, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, &...
Show moreSnyder, Michael, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, & Atmospheric Science
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Abstract/Description: The rapid development and sub-synoptic scale nature of the Genoa low in the Mediterranean Sea poses a forecasting challenge for United States Air Force (USAF). The Genoa low is a high-impact event for several Department of Defense (DOD) locations located in southern Europe, especially in the Po River Valley of northern Italy. This study evaluates the predictability and dynamics of the Genoa low extending to a 4-day event lead time as is required by the mission protocols at the affected...
Show moreThe rapid development and sub-synoptic scale nature of the Genoa low in the Mediterranean Sea poses a forecasting challenge for United States Air Force (USAF). The Genoa low is a high-impact event for several Department of Defense (DOD) locations located in southern Europe, especially in the Po River Valley of northern Italy. This study evaluates the predictability and dynamics of the Genoa low extending to a 4-day event lead time as is required by the mission protocols at the affected locations. Two Genoa low case studies are analyzed: 16 Feb 2015 (case 1), and 13 July 2016 (case 2), using the COnsortium for Small-scale MOdeling Limited-area Ensemble Prediction System (COSMO-LEPS). Ensemble prediction systems provide a range of possible forecast outcomes given the uncertainty in initial conditions, boundary conditions, as well as model physics. As such, ensembles are used to assess and analyze the predictability of the Genoa low. The analysis demonstrates several key findings concerning the Genoa low. The Genoa low is only weakly predictable at a lead time of 4 days. It is shown that only a small fraction of ensemble members (approximately 25%) met the Genoa low verification thresholds at this lead time. Ensemble spaghetti plots and maps of the ensemble variance show that the possibility of low formation at longer lead times is most effectively visualized using maps of ensemble variance. Traditional postage-stamp plots and minimum MSLP plots contain too much noise and variability to permit a forecaster to extract a signal indicating possible low formation. The formation of the Genoa low is associated with strong mistral winds. It is demonstrated that all ensemble simulations that were successful in identifying cyclogenesis also produce strong mistral winds, i.e., the strength of the mistral winds is anti-correlated to the minimum MSLP of the Genoa low. This linkage implies a potential dynamical connection between the two features. Further investigation shows that the mistral jet may exert an organizing influence on the Genoa low via a vorticity seeding mechanism. Time-lagged correlations show that the mistral jet amplifies several hours prior to cyclogenesis. The amplification is associated with mesoscale vorticity generation on the eastern periphery of the jet. These vorticity centers were subsequently shed into the target region where cyclogenesis occurs. Such a small-scale and rapid-developing dynamical link between the mistral winds and the Genoa low implies a limit on the predictability of the Genoa low. This study concludes that weather forecasting operations in the USAF would benefit from expansion of current ensemble prediction systems, not only for the purpose of improving the Genoa low forecast process and performance but also to better inform the mission planners of the limitations and uncertainties of predicting the Genoa low.
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Date Issued: 2017
Identifier: FSU_2017SP_Snyder_fsu_0071N_13906
Format: Thesis

Title: The Impact of Microstructure on an Accurate Snow Scattering Parameterization at Microwave Wavelengths.
Creator: Honeyager, Ryan Erick, Liu, Guosheng, Gunzburger, Max D., Ahlquist, Jon E., Ellingson, R. G., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of...
Show moreHoneyager, Ryan Erick, Liu, Guosheng, Gunzburger, Max D., Ahlquist, Jon E., Ellingson, R. G., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: High frequency microwave instruments are increasingly used to observe ice clouds and snow. These instruments are significantly more sensitive than conventional precipitation radar. This is ideal for analyzing ice-bearing clouds, for ice particles are tenuously distributed and have effective densities that are far less than liquid water. However, at shorter wavelengths, the electromagnetic response of ice particles is no longer solely dependent on particle mass. The shape of the ice particles...
Show moreHigh frequency microwave instruments are increasingly used to observe ice clouds and snow. These instruments are significantly more sensitive than conventional precipitation radar. This is ideal for analyzing ice-bearing clouds, for ice particles are tenuously distributed and have effective densities that are far less than liquid water. However, at shorter wavelengths, the electromagnetic response of ice particles is no longer solely dependent on particle mass. The shape of the ice particles also plays a significant role. Thus, in order to understand the observations of high frequency microwave radars and radiometers, it is essential to model the scattering properties of snowflakes correctly. Several research groups have proposed detailed models of snow aggregation. These particle models are coupled with computer codes that determine the particles' electromagnetic properties. However, there is a discrepancy between the particle model outputs and the requirements of the electromagnetic models. Snowflakes have countless variations in structure, but we also know that physically similar snowflakes scatter light in much the same manner. Structurally exact electromagnetic models, such as the discrete dipole approximation (DDA), require a high degree of structural resolution. Such methods are slow, spending considerable time processing redundant (i.e. useless) information. Conversely, when using techniques that incorporate too little structural information, the resultant radiative properties are not physically realistic. Then, we ask the question, what features are most important in determining scattering? This dissertation develops a general technique that can quickly parameterize the important structural aspects that determine the scattering of many diverse snowflake morphologies. A Voronoi bounding neighbor algorithm is first employed to decompose aggregates into well-defined interior and surface regions. The sensitivity of scattering to interior randomization is then examined. The loss of interior structure is found to have a negligible impact on scattering cross sections, and backscatter is lowered by approximately five percent. This establishes that detailed knowledge of interior structure is not necessary when modeling scattering behavior, and it also provides support for using an effective medium approximation to describe the interiors of snow aggregates. The Voronoi diagram-based technique enables the almost trivial determination of the effective density of this medium. A bounding neighbor algorithm is then used to establish a greatly improved approximation of scattering by equivalent spheroids. This algorithm is then used to posit a Voronoi diagram-based definition of effective density approach, which is used in concert with the T-matrix method to determine single-scattering cross sections. The resulting backscatters are found to reasonably match those of the DDA over frequencies from 10.65 to 183.31 GHz and particle sizes from a few hundred micrometers to nine millimeters in length. Integrated error in backscatter versus DDA is found to be within 25% at 94 GHz. Errors in scattering cross-sections and asymmetry parameters are likewise small. The observed cross-sectional errors are much smaller than the differences observed among different particle models. This represents a significant improvement over established techniques, and it demonstrates that the radiative properties of dense aggregate snowflakes may be adequately represented by equal-mass homogeneous spheroids. The present results can be used to supplement retrieval algorithms used by CloudSat, EarthCARE, Galileo, GPM and SWACR radars. The ability to predict the full range of scattering properties is potentially also useful for other particle regimes where a compact particle approximation is applicable.
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Date Issued: 2017
Identifier: FSU_2017SP_Honeyager_fsu_0071E_13726
Format: Thesis

Title: A Climatology of Tropical Cyclone Size in the Western North Pacific Using an Alternative Metric.
Creator: McKenzie, Thomas B. (Thomas Brian), Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department...
Show moreMcKenzie, Thomas B. (Thomas Brian), Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: The size of a tropical cyclone (TC) is a critical structure parameter that is associated with the greatest extent of societal impacts, and it can be estimated by several different metrics depending on the variable used. In this study, a revised method of quantifying the size of a TC is introduced. This method expands upon the work of Merrill (1984) to present an alternative tropical cyclone size parameter that uses the surface pressure field and the area enclosed by it. This new approach is...
Show moreThe size of a tropical cyclone (TC) is a critical structure parameter that is associated with the greatest extent of societal impacts, and it can be estimated by several different metrics depending on the variable used. In this study, a revised method of quantifying the size of a TC is introduced. This method expands upon the work of Merrill (1984) to present an alternative tropical cyclone size parameter that uses the surface pressure field and the area enclosed by it. This new approach is made possible by higher resolution and more accurate gridded meteorological data. The revised method measures the relative area of each closed isobar around a tropical cyclone to compute the area ratio of adjacent isobars. These calculations are then compared with an analytical area ratio derived from Holland (1980). The outermost closed isobar (OCI) is generally determined to be the most outward isobar whose area ratio does not significantly depart from the analytical ratio derived from Holland (1980). The algorithm is applied to a 36-year Western North Pacific (WNP) tropical cyclone data set (1979 – 2014), and the results of this are analyzed statistically and physically. This derived climatology utilized three reanalysis data sets: NASA's Modern-Era Retrospective Reanalysis data set (MERRA), ECMWF's ERA-Interim reanalysis (ERA-I), and NCEP's Climate Forecast System Reanalysis database (CFSR). On average, the algorithm was able to successfully determine an OCI for 75 – 80% of the 6-h best-track storm fixes. The primary reason for the inability of the algorithm to determine an OCI was poor representation of the TC in the gridded reanalysis, especially at and soon after formation. The statistical analysis reveals that TC size measurements using the revised metric is generally in agreement with existing climatologies. These results include a maximum mean TC size in October, a positive relationship between size and age of a TC, interannual variability of size, and an apparent maximum size near 25 degrees North. When the small-sized TCs at formation were compared to the large-sized TCs at formation, it was found that there was a highly statistically significant difference in the geographic distribution of these two groups. The size and position of the monsoon trough, in articular, generally determines where and how a TC forms in the WNP. The expected growth of a TC throughout later in its life cycle, especially during extratropical transition, was well-represented by this analysis. The study concludes with an examination of several case studies representative of the analysis presented above.
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Date Issued: 2017
Identifier: FSU_2017SP_McKenzie_fsu_0071N_13754
Format: Thesis

Title: Spatio-Temporal Evolutions of Non-Orthogonal Equatorial Wave Modes Derived from Observations.
Creator: Barton, Cory, Cai, Ming, Niu, Xufeng, Clarke, Allan J., Speer, Kevin G. (Kevin George), Sura, Philip, Florida State University, College of Arts and Sciences, Program in...
Show moreBarton, Cory, Cai, Ming, Niu, Xufeng, Clarke, Allan J., Speer, Kevin G. (Kevin George), Sura, Philip, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: Equatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to...
Show moreEquatorial waves have been studied extensively due to their importance to the tropical climate and weather systems. Historically, their activity is diagnosed mainly in the wavenumber-frequency domain. Recently, many studies have projected observational data onto parabolic cylinder functions (PCFs), which represent the meridional structure of individual wave modes, to attain time-dependent spatial wave structures. The non-orthogonality of wave modes has yet posed a problem when attempting to separate data into wave fields where the waves project onto the same structure functions. We propose the development and application of a new methodology for equatorial wave expansion of instantaneous flows using the full equatorial wave spectrum. By creating a mapping from the meridional structure function amplitudes to the equatorial wave class amplitudes, we are able to diagnose instantaneous wave fields and determine their evolution. Because all meridional modes are shared by some subset of the wave classes, we require constraints on the wave class amplitudes to yield a closed system with a unique solution for all waves' spatial structures, including IG waves. A synthetic field is analyzed using this method to determine its accuracy for data of a single vertical mode. The wave class spectra diagnosed using this method successfully match the correct dispersion curves even if the incorrect depth is chosen for the spatial decomposition. In the case of more than one depth scale, waves with varying equivalent depth may be similarly identified using the dispersion curves. The primary vertical mode is the 200 m equivalent depth mode, which is that of the peak projection response. A distinct spectral power peak along the Kelvin wave dispersion curve for this value validates our choice of equivalent depth, although the possibility of depth varying with time and height is explored. The wave class spectra diagnosed assuming this depth scale mostly match their expected dispersion curves, showing that this method successfully partitions the wave spectra by calculating wave amplitudes in physical space. This is particularly striking because the time evolution, and therefore the frequency characteristics, is determined simply by a timeseries of independently-diagnosed instantaneous horizontal fields. We use the wave fields diagnosed by this method to study wave evolution in the context of the stratospheric QBO of zonal wind, confirming the continuous evolution of the selection mechanism for equatorial waves in the middle atmosphere. The amplitude cycle synchronized with the background zonal wind as predicted by QBO theory is present in the wave class fields even though the dynamics are not forced by the method itself. We have additionally identified a time-evolution of the zonal wavenumber spectrum responsible for the amplitude variability in physical space. Similar to the temporal characteristics, the vertical structures are also the result of a simple height cross-section through multiple independently-diagnosed levels.
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Date Issued: 2016
Identifier: FSU_2016SP_Barton_fsu_0071E_13099
Format: Thesis

Title: Tracking and Analysis of Mesoscale Convective Systems over Central Equatorial Africa.
Creator: Hartman, Adam, Nicholson, Sharon E., Chagnon, Jeffrey M., Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric...
Show moreHartman, Adam, Nicholson, Sharon E., Chagnon, Jeffrey M., Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Mesoscale convective systems (MCSs) provide much of the annual rainfall over central equatorial Africa (CEA) during the March-April-May (MAM) and September-October-November (SON) rainy seasons. The characteristics and propagation of these systems are essential components to rainfall variability in this region. This has economic implications related to agriculture, livestock, and drought monitoring. Understanding MCSs will lead to better regional and global climate models that help predict the...
Show moreMesoscale convective systems (MCSs) provide much of the annual rainfall over central equatorial Africa (CEA) during the March-April-May (MAM) and September-October-November (SON) rainy seasons. The characteristics and propagation of these systems are essential components to rainfall variability in this region. This has economic implications related to agriculture, livestock, and drought monitoring. Understanding MCSs will lead to better regional and global climate models that help predict the effects of the changing hydrologic cycle and heat budget as they relate to MCS activity. This study identifies and tracks MCSs for the 33-year period 1983-2015 using GridSat-B1 cloud top temperature (CTT) data. Characteristics of the MCSs (displacement, duration, speed, heading, minimum CTT, and maximum size) are determined for the MAM and SON rainy seasons. Statistical significance testing is performed to determine if there are differences between the seasons as they relate to the variables and MCS counts. Long-term trends are also examined. Differences and trends are analyzed using the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR). This study finds statistically significant differences between the rainy seasons domain-wide, but these differences are variable- and latitude-dependent. There is high interannual variability and weak-to-absent trends for nearly all variables in both seasons. The exceptions are the average minimum CTTs, which show less interannual variability and cooling trends. Differences between the seasons are largely due to changes in low-level equivalent potential temperature and large scale circulations. The primary factor for initiation is thought to be thermally-driven gravity waves in the lee of the Great Rift Valley. Low-level vertical wind shear is believed to contribute to the maintenance of MCSs as they propagate, but do not seem to be a major factor for initiation.
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Date Issued: 2016
Identifier: FSU_FA2016_Hartman_fsu_0071N_13642
Format: Thesis

Title: Expanding the Utility of GOES-R with Improved Assimilation of Lightning and Infrared Satellite Observations.
Creator: Marchand, Max, Fuelberg, Henry E., Elsner, James B., Hart, Robert E. (Robert Edward), Liu, Guosheng, Misra, Vasubandhu, Florida State University, College of Arts and Sciences,...
Show moreMarchand, Max, Fuelberg, Henry E., Elsner, James B., Hart, Robert E. (Robert Edward), Liu, Guosheng, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: This study develops nudging methods of data assimilation that will expand the utility of the forthcoming GOES-R satellite series by including data from the Geostationary Lightning Mapper (GLM) and Advanced Baseline Imager (ABI). We develop a method to help trigger storms where lightning is observed, but no storm in simulated. Another method suppresses spurious simulated storms based on estimates of satellite-derived cloud top height (CTH) that will be improved due to the increased number of...
Show moreThis study develops nudging methods of data assimilation that will expand the utility of the forthcoming GOES-R satellite series by including data from the Geostationary Lightning Mapper (GLM) and Advanced Baseline Imager (ABI). We develop a method to help trigger storms where lightning is observed, but no storm in simulated. Another method suppresses spurious simulated storms based on estimates of satellite-derived cloud top height (CTH) that will be improved due to the increased number of infrared channels on the ABI. In lieu of GOES-R data, Earth Networks Total Lightning Network (ENTLN) observations and GOES-13 10.7-micron observations are used in the current research. The assimilation methods are developed and evaluated using the Weather Research and Forecasting (WRF) model at convection-permitting scales (3-km horizontal grid spacing). We verify precipitation simulations against NCEP Stage IV hourly precipitation observations by computing fraction skill score (FSS; a neighborhood approach) and frequency bias for three case days. Simulated temperature, winds, humidity, and surface pressure are also verified against METAR surface observations. Our new method of assimilating lightning observations nudges low-level vertical velocity to trigger storms. This method is compared to a previous method that nudges low-level temperature (MU). Both lightning assimilation methods then are combined with the assimilation of CTH. CTH assimilation removes hydrometeors above the CTH estimate and applies an amount of cooling that is proportional to the latent heat of the removed hydrometeors to suppress spurious convection. Without applying CTH assimilation, the MU method produces better precipitation forecasts in terms of FSS than our optimal configuration of the vertical velocity nudging (WNO) method. However, if WNO is applied together with CTH assimilation, WNO produces FSS during the forecast period similar to MU applied with CTH assimilation. MU generally produces stronger storms than WNO that cause more mesoscale subsidence and indirect suppression of spurious storms. Direct suppression during CTH assimilation diminishes the impact of the indirect suppression. CTH assimilation also provides greater convective available potential energy that supports the weaker WNO storms. Regardless of whether CTH assimilation is applied, WNO generally produces superior forecasts of surface fields relative to MU and a control that employs no assimilation. This improvement is 1-6% of root mean square error during a 12-h forecast period subsequent to assimilation. Lightning assimilation (WNO or MU) combined with CTH assimilation typically provides the best precipitation forecasts. These are better than the control during the first 6-12 h of the forecast period for 1-mm and 10-mm precipitation thresholds. This combined assimilation method with the operation of GOES-R enables assimilation of clouds and storms over areas devoid of quality radar, including mountainous terrain, ocean basins, and Central and South America.
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Date Issued: 2016
Identifier: FSU_FA2016_Marchand_fsu_0071E_13523
Format: Thesis

Title: An Examination of Boreal Summer Sahel Rainfall Variability in the Context of the Tropical Easterly Jet.
Creator: King, Sidney E. (Sidney Earle), Nicholson, Sharon E., Chagnon, Jeffrey M., Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean,...
Show moreKing, Sidney E. (Sidney Earle), Nicholson, Sharon E., Chagnon, Jeffrey M., Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: The movement of precipitation around the Earth has an integral impact on fresh water availability, vegetation, and the occurrence of natural disasters, and therefore human society at large. In the African Sahel, the rainfall is the limiting factor in agriculture and the most variable characteristic of climate both spatially and temporally. In light of recent famine concerns, research on rainfall variability in the Sahel is critical as well as timely. A review of climate and environmental...
Show moreThe movement of precipitation around the Earth has an integral impact on fresh water availability, vegetation, and the occurrence of natural disasters, and therefore human society at large. In the African Sahel, the rainfall is the limiting factor in agriculture and the most variable characteristic of climate both spatially and temporally. In light of recent famine concerns, research on rainfall variability in the Sahel is critical as well as timely. A review of climate and environmental literature provided a perspective and a set of methodologies upon which the research could build. This research emphasizes the role of the regional and global atmospheric circulation in governing the variability of Sahel rainfall. It examines the changing spatiotemporal characteristics of the rainfall regime in the context of the Tropical Easterly Jet (TEJ), the El Nino/Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), and the Tibetan High. Historical data was obtained from the African rain gauge network, NCEP/NCAR Reanalysis 1, and HadISST version 1.1. The results of this study show that the relationship between the TEJ and Sahel rainfall is a casual one, with a stronger TEJ enhancing upper-level divergence to promote broader, more intense vertical ascent. It also showed that diagnostic variables relevant to the general circulation, such as the maximum ascent within the rainbelt, the northward displacement of the AEJ, and the advection of precipitable water over the Sahel have a robust positive relationship with the Sahel rainfall anomaly due to the influence of the TEJ. The results also determined that a significant relationship exists in terms of the high-frequency interannual variability between negative ENSO events and the strengthening of the TEJ, which would similarly lead to anomalously wet years in the Sahel during a negative ENSO anomaly. This study posits a new framework for understanding rainfall variability in the Sahel due to its focus on the impacts of the atmospheric circulation. Furthermore, it can have important applications to understanding and forecasting droughts and floods in the Sahel, improve the modeling of Sahel climate, and provide a basis for further study of how West Africa and the TEJ fit into the global picture.
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Date Issued: 2016
Identifier: FSU_FA2016_King_fsu_0071N_13651
Format: Thesis

Title: Wave and Wind Direction Effects on Ocean Surface Emissivity Measurements in High Wind Conditions.
Creator: Holbach, Heather Marie, Bourassa, Mark Allan, McGee, Daniel, Hart, Robert E. (Robert Edward), Liu, Guosheng, Clarke, Allan J., Uhlhorn, Eric, Powell, Mark Dillon, Florida State...
Show moreHolbach, Heather Marie, Bourassa, Mark Allan, McGee, Daniel, Hart, Robert E. (Robert Edward), Liu, Guosheng, Clarke, Allan J., Uhlhorn, Eric, Powell, Mark Dillon, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Wave and wind direction effects on remote sensing measurements of ocean surface emissivity are investigated using a microwave radiometer in high wind conditions with a focus on tropical cyclones. Surface wind speed, which drives many atmospheric and oceanic phenomena, can be inferred from the ocean surface emissivity measurements through the use of a radiative transfer model and inversion algorithm. The accuracy of the ocean surface emissivity to wind speed calibration relies on accurate...
Show moreWave and wind direction effects on remote sensing measurements of ocean surface emissivity are investigated using a microwave radiometer in high wind conditions with a focus on tropical cyclones. Surface wind speed, which drives many atmospheric and oceanic phenomena, can be inferred from the ocean surface emissivity measurements through the use of a radiative transfer model and inversion algorithm. The accuracy of the ocean surface emissivity to wind speed calibration relies on accurate knowledge of the surface variables that are influencing the ocean surface emissivity. This study will identify an asymmetry in ocean surface emissivity measurements at off-nadir incidence angles that is related to the surface wind direction modifying the distribution of whitewater coverage, which is composed of active whitecaps and residual foam that persists after wave breaking, on the ocean surface in high wind conditions viewed by the radiometer. It will also be shown that asymmetries are present in ocean surface emissivity measurements from a nadir pointing instrument in hurricanes. This asymmetry can be related to swell and wind wave propagation directions with respect to the wind direction modifying the stress on the ocean surface, which presumably impacts the wave breaking and thus the whitewater coverage characteristics on the ocean surface. These results help achieve the study goals: 1) improving the understanding of how wave and wind direction modify ocean surface emissivity in high wind conditions and 2) identifying conditions, particularly in tropical cyclones, where wind direction and sea state modify the ocean surface emissivity and should be considered in order to further improve algorithms for the remote sensing of the surface wind.
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Date Issued: 2016
Identifier: FSU_FA2016_Holbach_fsu_0071E_13475
Format: Thesis

Title: WRF Simulations of Water Vapor Content for TC Ingrid (September 2013).
Creator: Allison, Thomas Daniel, Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Holmes, Christopher D., Florida State University, College of Arts and Sciences,...
Show moreAllison, Thomas Daniel, Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Misra, Vasubandhu, Holmes, Christopher D., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Atmospheric water vapor is a potent greenhouse gas, and its variations in the upper troposphere and lower stratosphere (UTLS) have important climate impacts. The water vapor budget of tropical cyclones (TCs) and their impact on the UTLS remain understudied. This paper describes high-resolution simulations of TC Ingrid during September 2013 using the Weather Research and Forecasting (WRF) model to calculate the water vapor budget. Using Ingrid as an example provides a better understanding of...
Show moreAtmospheric water vapor is a potent greenhouse gas, and its variations in the upper troposphere and lower stratosphere (UTLS) have important climate impacts. The water vapor budget of tropical cyclones (TCs) and their impact on the UTLS remain understudied. This paper describes high-resolution simulations of TC Ingrid during September 2013 using the Weather Research and Forecasting (WRF) model to calculate the water vapor budget. Using Ingrid as an example provides a better understanding of water vapor transport into the UTLS by TCs, helping to answer a question posed during NASA’s Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling through Regional Surveys (SEAC4RS), specifically whether water vapor transport in TCs hydrates or dehydrates the UTLS. Our WRF simulations of TC Ingrid closely correspond to the National Hurricane Center’s Best Track data. We also evaluate model results of the water vapor budget with in situ airborne data of Ingrid collected during the SEAC4RS mission. Satellite imagery also is used to validate the simulated structure of Ingrid. We show spatial and temporal changes of UTLS water vapor throughout Ingrid's lifecycle to determine whether and how TCs hydrate or dehydrate the UTLS. Results show that TCs do transport large quantities of water vapor into the UTLS, and overshooting deep convection is an especially potent transport method. The paper sheds light on mechanisms that inject water vapor into the UTLS and on the widespread horizontal and vertical transports of water vapor within TCs.
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Date Issued: 2016
Identifier: FSU_FA2016_Allison_fsu_0071N_13632
Format: Thesis

Title: A Teleconnection between Subtropical Convection and Higher Latitude Wave Activity in the Atlantic.
Creator: Cruz, Antonio DeJesus, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean,...
Show moreCruz, Antonio DeJesus, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Rossby waves are waves in potential vorticity that propagate along the extratropical tropopause and can be impacted by the advection of low-PV air originating from the subtropics. In this study, the subtropical precipitation influence on the extratropical Rossby wave activity during the Atlantic winter season is investigated for a ten year period. Using both TRMM and TIGGE 12-Hr forecasted precipitation data, heavy precipitation events were identified near the footprints regions of warm...
Show moreRossby waves are waves in potential vorticity that propagate along the extratropical tropopause and can be impacted by the advection of low-PV air originating from the subtropics. In this study, the subtropical precipitation influence on the extratropical Rossby wave activity during the Atlantic winter season is investigated for a ten year period. Using both TRMM and TIGGE 12-Hr forecasted precipitation data, heavy precipitation events were identified near the footprints regions of warm conveyor belts in the northern Atlantic, specifically in the Gulf of Mexico and Bermuda region. The extratropical Rossby waves were then analyzed using PV on a 320K surface. By use of wavelet transforms, the amplitude of the Rossby waves were analyzed as a function of wavelength and longitude. The interaction between a single heavy precipitation event and the extratropical Rossby waves was examined for the days preceding and the week following the event. A climatological analysis of heavy precipitation events was conducted on the winter seasons from 2006 - 2015. Case study and climatological analysis identified the following: A ridge in the Northern Atlantic undergoes amplification downstream of the heavy precipitation event in the days following the event. A southerly flow, likely associated with a warm conveyor belt, connects the region of the heavy precipitation event and the extratropical tropopause. The interaction was most prominent during the late winter season and during the heaviest of precipitation events. The teleconnection identified in this study highlights a mechanism by which cloud-scale subtropical precipitation is connected to synoptic scale extratropical dynamics in the Atlantic.
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Date Issued: 2016
Identifier: FSU_FA2016_Cruz_fsu_0071N_13650
Format: Thesis

Title: Sea-Ice, Clouds and Atmospheric Conditions in the Arctic and Their Interactions as Derived from a Merged C3M Data Product.
Creator: Nag, Bappaditya, Cai, Ming, Tam, Christopher K. W., Clarke, Allan J., Liu, Guosheng, Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences,...
Show moreNag, Bappaditya, Cai, Ming, Tam, Christopher K. W., Clarke, Allan J., Liu, Guosheng, Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: The polar regions of the world constitute an important sector in the global energy balance. Among other effects responsible for the change in the sea-ice cover like ocean circulation and ice-albedo feedback, the cloud-radiation feedback also plays a vital role in modulation of the Arctic environment. However the annual cycle of the clouds is very poorly represented in current global circulation models. This study aimed to explore the atmospheric conditions in the Arctic on an unprecedented...
Show moreThe polar regions of the world constitute an important sector in the global energy balance. Among other effects responsible for the change in the sea-ice cover like ocean circulation and ice-albedo feedback, the cloud-radiation feedback also plays a vital role in modulation of the Arctic environment. However the annual cycle of the clouds is very poorly represented in current global circulation models. This study aimed to explore the atmospheric conditions in the Arctic on an unprecedented spatial coverage spanning 70°N to 80°N through the use of a merged data product, C3MData (derived from NASA's A-Train Series). The following three topics provide outline on how this dataset can be used to accomplish a detailed analysis of the Arctic environment and provide the modelling community with first information to update their models aimed at better forecasts. (1)The three properties of the Arctic climate system to be studied using the C3MData are sea-ice, clouds, and the atmospheric conditions. The first topic is to document the present states of the three properties and also their time evolutions or their seasonal cycles. (2)The second topic is aimed at the interactions or the feedbacks processes among the three properties. For example, the immediate alteration in the fluxes and the feedbacks arising from the change in the sea-ice cover is investigated. Seasonal and regional variations are also studied. (3)The third topics is aimed at the processes in native spatial resolution that drive or accompany with sea ice melting and sea ice growth. Using a composite approach based on a classification due to surface type, it is found that limitation of the water vapour influx from the surface due to change in phase at the surface featuring open oceans or marginal sea-ice cover to complete sea-ice cover is a major determinant in the modulation of the atmospheric moisture. The impact of the cloud-radiative effects in the Arctic is found to vary with sea-ice cover and seasonally. The effect of the marginal sea-ice cover becomes more and more pronounced in the winter. The seasonal variation of the dependence of the atmospheric moisture on the surface and the subsequent feedback effects is controlled by the atmospheric stability measured as a difference between the potential temperature at the surface and the 700hPa level. A regional analysis of the same suggests that most of the depiction of the variations observed is contributed from the North Atlantic region.
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Date Issued: 2016
Identifier: FSU_2016SU_Nag_fsu_0071E_13367
Format: Thesis

Title: Diabatic Processes Modifying the Structure and Evolution of Idealized Baroclinic Life Cycle Simulations.
Creator: Glasser, Daisy, Chagnon, Jeffrey M., Cai, Ming, Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: Diabatic processes including latent heating and radiation are parameterized in numerical weather prediction (NWP) models and constitute a major source of error. Isolating the extent of diabatic modification in an extratropical cyclone in observational atmospheric data is difficult. This study analyzes four idealized Advanced Weather Research and Forecasting (WRF-ARW) model sensitivity experiments in which radiation or moisture are either included or withheld. The experiments consist of the...
Show moreDiabatic processes including latent heating and radiation are parameterized in numerical weather prediction (NWP) models and constitute a major source of error. Isolating the extent of diabatic modification in an extratropical cyclone in observational atmospheric data is difficult. This study analyzes four idealized Advanced Weather Research and Forecasting (WRF-ARW) model sensitivity experiments in which radiation or moisture are either included or withheld. The experiments consist of the following: no radiation and no moisture (NRNM), radiation and no moisture (RNM), moisture and no radiation (NRM), and radiation and moisture (RM). Simulations are of an idealized baroclinic wave in the midlatitudes. Because baroclinic waves are associated with synoptic scale weather events, these WRF-ARW simulations are the ideal platform to better understand the interactions of diabatic and dynamic processes. Inclusion of moisture and radiation has a significant impact on baroclinic wave structure and evolution. On the synoptic scale, the RM experiment demonstrates greatest amplification/depth, earliest growth, and was the only experiment with cyclonic breaking in the troposphere and high amplitude anticyclonic breaking in the lower stratosphere. On the sub-synoptic scale, vertical dipoles in isentropic potential vorticity (IPV) and cloud-scale anomalies developed in the middle to upper troposphere as the wave matured. While radiation alone yields no anomaly, and moisture alone yields a small anomaly, the inclusion of radiation and moisture together yields a significantly larger IPV anomaly. Anomalies may be due to constructive interference or nonlinear feedbacks between radiative cooling and latent heating. Results of this study have important implications for NWP, especially in the representation of physical processes via parameterization schemes. Knowledge gained about physical processes and their feedbacks on resolved flow might help to better understand error and bias in NWP models.
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Date Issued: 2016
Identifier: FSU_2016SU_Glasser_fsu_0071N_13462
Format: Thesis

Title: Surface and Atmospheric Boundary Layer Responses to Diurnal Variations of Sea Surface Temperature in an NWP Model.
Creator: Weihs, Rachel R. (Rachel Rebecca), Bourassa, Mark Allan, Harper, Kristine, Misra, Vasubandhu, Sura, Philip, Clarke, Allan J., Florida State University, College of Arts and...
Show moreWeihs, Rachel R. (Rachel Rebecca), Bourassa, Mark Allan, Harper, Kristine, Misra, Vasubandhu, Sura, Philip, Clarke, Allan J., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: An atmospheric model is coupled to a sea surface temperature algorithm that calculates the diurnal variability in order to understand the responses to near surface winds and boundary layer temperature, pressure, and moisture in the north Central Atlantic. 7-day case study simulations with diurnally varying sea surface temperatures and daily-constant sea surface temperatures are compared. With the inclusion of diurnal heating during the day, the local heat fluxes are increased and the surface...
Show moreAn atmospheric model is coupled to a sea surface temperature algorithm that calculates the diurnal variability in order to understand the responses to near surface winds and boundary layer temperature, pressure, and moisture in the north Central Atlantic. 7-day case study simulations with diurnally varying sea surface temperatures and daily-constant sea surface temperatures are compared. With the inclusion of diurnal heating during the day, the local heat fluxes are increased and the surface pressure decreases. The extent of the surface-induced heating to the atmosphere is not necessarily restricted to the boundary layer depending on the atmospheric stability and the interaction with synoptic scale weather. The diurnal variations in sea surface temperature also induce positive and negative mean wind speed anomalies on the order of 0.5 m/s over the 7-day period. Hourly changes to the wind field, however, can exceed 3 m/s particularly where modifications to the regional weather occur. A comparison to geostationary data show that the sea surface temperature algorithm overestimates the warming on average, but this overestimation could be exaggerated from several factors including smoothing of the geostationary data. We examine the spatial variability and data distribution of the wind field anomalies in response to the diurnal sea surface temperature gradients at hourly and daily time scales. The changes to the wind field on the first day of diurnal warming exhibit a linear, but temporally lagged response to the direction in which flow crosses the diurnal warming gradient. This trend was also observed on day 2, but does not exist for subsequent days after. It is thought that the larger amplitude responses of interaction with the synoptic scale (secondary feedbacks) dominate the distribution for areas in which we expect wind-sea surface temperature coupling. The surface pressure gradient and Coriolis are deemed the dominant forcing processes in the model that generate the initial wind-diurnal sea surface temperature coupling response on the first day of the simulation. In order to understand the importance of interactive feedbacks of the wind and the diurnal cycle of sea surface temperatures, we compared the duration and amplitude of the diurnal warming produced in a one-way coupled simulation. The one-way coupled simulation allows the diurnal variations in sea surface temperature to influence the surface fluxes at the concurrent time step, but uses winds from a non-diurnally modified SST to calculate the diurnal warming of the sea surface temperature. As compared to two-way coupled simulations, the mean amplitude of the diurnal warming is larger and the duration is longer. This is one way to demonstrate that the integrated hourly feedbacks to the diurnal variability of sea surface temperature are important in producing an accurate duration and amplitude of diurnal heating over the day.
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Date Issued: 2016
Identifier: FSU_2016SU_Weihs_fsu_0071E_13436
Format: Thesis

Title: A Climatological Analysis of the Extratropical Flow Response to Recurving North Atlantic Tropical Cyclones.
Creator: Visin, Lauren Elizabeth, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Fuelberg, Henry E., Florida State University, College of Arts and Sciences, Department of Earth,...
Show moreVisin, Lauren Elizabeth, Chagnon, Jeffrey M., Hart, Robert E. (Robert Edward), Fuelberg, Henry E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: This study investigates the response of the extratropical jet to recurving North Atlantic tropical cyclones (TCs). A joint climatology of north Atlantic recurving TCs from 2007-2013 and Rossby waves on the extratropical jet is presented. Using a potential vorticity (PV) framework, Rossby wave breaking (RWB) and trough/ridge amplitude were quantified in order to evaluate jet characteristics downstream from recurving TCs. Additionally, the meridional PV gradient was evaluated to attempt to...
Show moreThis study investigates the response of the extratropical jet to recurving North Atlantic tropical cyclones (TCs). A joint climatology of north Atlantic recurving TCs from 2007-2013 and Rossby waves on the extratropical jet is presented. Using a potential vorticity (PV) framework, Rossby wave breaking (RWB) and trough/ridge amplitude were quantified in order to evaluate jet characteristics downstream from recurving TCs. Additionally, the meridional PV gradient was evaluated to attempt to isolate a possible interaction mechanism. The extratropical jet is disturbed downstream of recurving TCs in the week following recurvature. RWB is made more likely in the week following recurvature, while suppression of RWB occurs at recurvature. Both ridge and trough amplitude increase downstream from recurving TCs in the week following recurvature, also supported by ridge amplification in composite PV anomalies. PV gradient modification remains unclear.
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Date Issued: 2016
Identifier: FSU_2016SU_Visin_fsu_0071N_13459
Format: Thesis

Title: Development and Evolution of Convective Bursts in WRF Simulations of Hurricanes Dean (2007) and Bill (2009).
Creator: Hazelton, Andrew Todd, Hart, Robert E. (Robert Edward), Chiorescu, Irinel, Bourassa, Mark Allan, Fuelberg, Henry E., Liu, Guosheng, Rogers, Robert Fulton, Florida State...
Show moreHazelton, Andrew Todd, Hart, Robert E. (Robert Edward), Chiorescu, Irinel, Bourassa, Mark Allan, Fuelberg, Henry E., Liu, Guosheng, Rogers, Robert Fulton, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Understanding and predicting the inner-core structure and intensity change of tropical cyclones (TCs) remains one of the biggest challenges in tropical meteorology. This study addresses this challenge by investigating the formation, structure, and intensity changes resulting from localized strong updrafts in TCs known as convective bursts (CBs). The evolution of CBs are analyzed in high-resolution simulations of two hurricanes (Dean 2007 and Bill 2009) using the Weather Research and...
Show moreUnderstanding and predicting the inner-core structure and intensity change of tropical cyclones (TCs) remains one of the biggest challenges in tropical meteorology. This study addresses this challenge by investigating the formation, structure, and intensity changes resulting from localized strong updrafts in TCs known as convective bursts (CBs). The evolution of CBs are analyzed in high-resolution simulations of two hurricanes (Dean 2007 and Bill 2009) using the Weather Research and Forecasting (WRF) model. The simulations are able to capture the observed track and peak intensity of the TCs. With Dean, there is a slight lag between the simulated intensification and actual intensification, and the extreme rate of RI is not fully captured. However, the cycle of intensification, weakening, and re-intensification observed in both TCs is captured in the simulations, and appears to be due to a combination of internal dynamics and the surrounding environmental conditions. CBs are identified based on the 99th percentile of eyewall vertical velocity (over the layer from z = 6-12 km) in each simulation (8.4 m s-1 for Dean, 5.4 m s-1 for Bill). The highest density of CBs is found in the downshear-left quadrant, consistent with prior studies. The structure of the CBs is analyzed by comparing r-z composites of azimuths with CBs and azimuths without CBs, using composite figures and statistical comparisons. The CB composites show stronger radial inflow in the lowest 0-2 km, and stronger radial outflow from the eye to the eyewall in the 2-4 km layer. The CB composites also have stronger low-level vorticity than the non-CBs, potentially due to eyewall mesovortices. The analysis of individual CBs also confirms the importance of the eye-eyewall exchange in CB development, potentially by providing buoyancy, as parcel trajectories show that many parcels are flung outward from the eye and rapidly ascend in the CBs, with as much as 500 J/kg of CAPE along the parcel path. In addition, the location of radial convergence seems to play a key role in governing the radial location of CBs. Inner-core CBs seem to be associated with local convergence maxima in the eyewall, while CBs outside the radius of maximum winds (RMW) are associated with convergence maxima due to bands and/or secondary eyewalls. Analysis of intensity change in the simulations shows that there are more inner-core CBs during times when the TCs are intensifying, while weakening/steady times appear to be associated with more CBs outside the radius of maximum wind (RMW), consistent with observational studies and theoretical work. However, times when the TC has already been intensifying and continues to do so have more CBs than times when the TC has been weakening but then intensifies. This suggests that CB development may not always be predictive, but rather may sometimes occur as a result of ongoing intensification. On the other hand, rapid intensification (RI) in the simulations is found to be associated with an even higher density of CBs inside the RMW than slower intensification. Lag correlations between CBs and intensity are calculated to investigate the time of the intensity response to CB development. These calculations reveal a broad peak in correlation, with the CBs tending to lead pressure falls by 0-3 hours. These results confirm the notion that convective heating inside the RMW is favorable for intensification. The findings from this analysis show that eyewall CBs are driven by asymmetric dynamical processes in the inner-core region of TCs, both in and above the TC boundary layer. In addition, the relationship between CB development and intensity change is indeed positive, sometimes in a predictive sense, and at other times while intensity change is ongoing.
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Date Issued: 2016
Identifier: FSU_2016SP_Hazelton_fsu_0071E_13072
Format: Thesis

Title: Relationship Between Meridional Mass Circulation and Extreme Temperature Events in the Southern Hemisphere.
Creator: Yan, Ruikai, Cai, Ming, Chagnon, Jeffrey M., Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: This study explores extreme surface temperature events in Southern Hemisphere winter (June – August) from 1979 to 2011 and their relation with meridional mass circulation by using daily ERA-interim Re-Analysis data from European Center for Medium-Range Weather Forecasts (ECMWF). Meridional mass circulation indices are developed to quantitatively represent the warm air mass being transported into the polar region in the upper atmosphere and the cold air mass being transported out of the polar...
Show moreThis study explores extreme surface temperature events in Southern Hemisphere winter (June – August) from 1979 to 2011 and their relation with meridional mass circulation by using daily ERA-interim Re-Analysis data from European Center for Medium-Range Weather Forecasts (ECMWF). Meridional mass circulation indices are developed to quantitatively represent the warm air mass being transported into the polar region in the upper atmosphere and the cold air mass being transported out of the polar region in the lower atmosphere. Our results show that weaker poleward warm air mass transport aloft is associated with weaker cold air transport toward equator in the lower troposphere, resulting in cold air being confined in the polar regions. Similarly, stronger poleward warm air mass transport in the upper atmosphere is related to stronger cold air transport out of the polar regions, causing enormous cold air outbreaks in the mid-latitude regions. We find that regions to the south of 45S exhibit a robust relationship between surface air temperature anomalies and meridional mass circulation. Weaker circulation is associated with abnormally cold in Antarctica and abnormally warm in regions from 45S to 60S. Conversely, stronger circulation is related to anomalously warm in Antarctica and anomalously cold in the surrounding continental shelf, particularly over Weddell-Scotia Sea and north Ross Sea where are the two preferred routes for cold air coming out of Antarctica. On the other hand, temperature anomalies over the regions north of 45S are not sensitive to the meridional circulation variability. The fact that surface air temperature anomalies over the Southern Ocean rarely exceed 4C suggests that cold air coming out of Antarctic has limited impacts on the Southern Ocean due to its large thermal inertia. In summary, the meridional mass circulation indices provide a robust diagnostics for extreme cold events in 45S - 90S domain very well, but may not be adequate to describe all cold events over the vast mid-latitude regions in the Southern Hemisphere.
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Date Issued: 2016
Identifier: FSU_2016SP_Yan_fsu_0071N_13259
Format: Thesis

Title: Characterizing the Onset and Demise of the Indian Summer Monsoon.
Creator: Noska, Ryne Garrett, Misra, Vasubandhu, Hart, Robert E. (Robert Edward), Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean...
Show moreNoska, Ryne Garrett, Misra, Vasubandhu, Hart, Robert E. (Robert Edward), Bourassa, Mark Allan, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: An objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one readily available variable, All-India rainfall (AIR), which has been reliably observed for more than a century. The proposed All-India rainfall onset and demise (AIROD) is shown to be insensitive to all recorded false onsets. By definition, the seasonal ISM rainfall anomalies become a function of the variations of onset and demise dates,...
Show moreAn objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one readily available variable, All-India rainfall (AIR), which has been reliably observed for more than a century. The proposed All-India rainfall onset and demise (AIROD) is shown to be insensitive to all recorded false onsets. By definition, the seasonal ISM rainfall anomalies become a function of the variations of onset and demise dates, with early onset and late demise resulting in greater season length and total seasonal rainfall. Seasonal rainfall itself is a strong predictor of the following ENSO phase and provides a more accurate depiction of the ISM than does the commonly-used June-September (JJAS) All-India monsoon rainfall (AIMR) index. This new index provides an accurate and comprehensive representation of the seasonal evolution of the ISM by capturing dramatic changes in large-scale dynamic (i.e. wind- and current-based) and thermodynamic (temperature- and moisture-based) variables, which is found to make the onset an especially important feature to monitor to understand the evolution of the ensuing monsoon season. In particular, the zonal (meridional) progression of 300hPa meridional temperature gradient (meridional ocean heat transport) reversal may be monitored about twenty days before onset to help determine the timing of its arrival. Interannual variability of ISM features and their associated large-scale phenomena are also analyzed. An early (late) onset corresponds to an increase (decrease) in anomalies of kinetic energy of 850hPa wind over the Arabian Sea and central Indian rainfall up to fifteen and ten days before onset, respectively. Conversely, an early (late) demise corresponds to a decrease (increase) in the aforementioned anomalies up to ten days after demise. Additionally, the preceding December-February ENSO phase is associated with the onset of the ISM, as an early (late) onset is preceded by La Niña (El Niño).
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Date Issued: 2016
Identifier: FSU_2016SP_Noska_fsu_0071N_13140
Format: Thesis

Title: Spatial Analyses of Climatological Effects on Hurricane Intensification Rates.
Creator: Fraza, Erik, Elsner, James B., Hart, Robert E. (Robert Edward), Uejio, Christopher K., Zhao, Tingting, Florida State University, College of Social Sciences and Public Policy,...
Show moreFraza, Erik, Elsner, James B., Hart, Robert E. (Robert Edward), Uejio, Christopher K., Zhao, Tingting, Florida State University, College of Social Sciences and Public Policy, Department of Geography
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Abstract/Description: The aim of these studies is to determine spatial climatological effects on hurricane intensification rates. Previous studies have noted that the skill in predict a hurricane's track has improved at a much greater rate than the skill to predict its intensity. There is even less research concerning hurricane intensification rates, let alone research done spatially and climatologically. Therefore, the research herein aims to understand what drives hurricane intensification rates. This is done by...
Show moreThe aim of these studies is to determine spatial climatological effects on hurricane intensification rates. Previous studies have noted that the skill in predict a hurricane's track has improved at a much greater rate than the skill to predict its intensity. There is even less research concerning hurricane intensification rates, let alone research done spatially and climatologically. Therefore, the research herein aims to understand what drives hurricane intensification rates. This is done by using spatial climatological analyses to determine the effects that intensity, sea surface temperatures (SSTs), ocean heat content (OHC), El Niño--Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Madden--Julian Oscillation (MJO), and the Pacific Decadal Oscillation (PDO) have on hurricane intensification rates. Using both equal-area hexagons and raster techniques, hurricane track data is plotted spatially. SST, ocean salinity, and OHC values are also represented on a spatial grid. Finally, climate variables are represented temporally as mean yearly values. A generalized linear model from a gamma family and a logarithmic link function, as well as a full probability model are used to determine the effects that the variables of interest have on hurricane intensification rates. It is found that intensity has a positive effect on hurricane intensification rates with an average increase of 0.024 ± 0.0032 m s⁻¹ in intensification for a 1 m s⁻¹ increase in intensity. SST is also found to have a positive effect on intensification rates with an average increase in hurricane intensification of 16% for a 1° C increase in mean SST. It is also found that decreased salinity may have a positive effect on hurricane intensification rates by inhibiting vertical mixing. In the North Atlantic basin, it is found that the NAO has a negative effect on intensification rates of ‒0.18 m s⁻¹ h⁻¹ per 1 SD, while ENSO and MJO do not have a statistically significant effect. In the Eastern North Pacific basin, it is found that both the NAO and ENSO have a positive effect on hurricane intensification rates, while the MJO and PDO do not have a statistically significant effect. Finally, in comparing the largest intensification rates during the most extreme NAO events in the North Atlantic basin, as well as the most extreme ENSO events in the Eastern North Pacific basin, it appears that rapid intensification (RI) may simply be normal intensification occurs over a longer time period. These studies confirm the previously held idea that warmer SSTs will lead to higher intensification rates. Along with this is the finding that the NAO has a negative effect on hurricane intensification rates in the North Atlantic basin. This was not something that was previously mentioned in the research. Finally, the idea that RI may not be due to small thermodynamic processes but instead normal intensification over a longer amount of time is an intriguing notion that deserves further analysis.
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Date Issued: 2016
Identifier: FSU_2016SP_Fraza_fsu_0071E_13062
Format: Thesis

Title: Adjustment of Visually Observed Ship Winds (Beaufort Winds) in ICOADS.
Creator: Li, Keqiao, Bourassa, Mark Allan, Smith, Shawn R. (Shawn Richard), Liu, Guosheng, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of...
Show moreLi, Keqiao, Bourassa, Mark Allan, Smith, Shawn R. (Shawn Richard), Liu, Guosheng, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: ABSTRACT The bias adjustment of visually estimated ship winds in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) is addressed through the comparison to the QuickSCAT scatterometer equivalent neutral winds. We assume that visually estimated winds and satellite scatterometer winds share similar characteristics, which are a function of stress rather than wind speed, and treat the estimated ship winds as equivalent neutral winds. Under such an assumption, we use statistical...
Show moreABSTRACT The bias adjustment of visually estimated ship winds in the International Comprehensive Ocean-Atmosphere Data Set (ICOADS) is addressed through the comparison to the QuickSCAT scatterometer equivalent neutral winds. We assume that visually estimated winds and satellite scatterometer winds share similar characteristics, which are a function of stress rather than wind speed, and treat the estimated ship winds as equivalent neutral winds. Under such an assumption, we use statistical analyses to calculate the bias correction for estimated ship winds. Because observation practices vary by country and data provider, ICOADS identifies datasets by "deck" which is a number that allows for differentiating the source of the records (different deck numbers indicate different data collections provided to ICOADS, each which may contain one or more sources/countries). Three ICOADS decks 792, 926, and 992 contain the vast majority (~90%) of collocated visually estimated ship winds covering the time period November 1999-October 2009. The Root-Mean-Square difference between these visually estimated ship winds and scatterometer winds are 3.0ms-1, 2.8ms-1 and 2.9ms-1 for each major deck respectively. Following the methodology of Freilich (1997) and Freilich and Dunbar (1999), we numerically show that for lower wind speeds (0ms-1-5ms-1 in this case) that the random error in the component of the visually estimated ship winds causes an artificial appearance of an overestimation relative to satellite scatterometer winds. We also extend this statistical artifact test to test higher wind speeds (12ms-1-18ms-1 in this case) through a Monte Carlo approach. An apparent slight drop of the conditional sample means relative to reference line is shown to be a statistical artifact. These artificial biases are properly accounted in this study. A new bias correction, LMS correction, is calculated and also compared to prior corrections such as Lindau (1995). This new bias correction is available for wind speeds ranging from 0ms-1 to 17ms-1, because there are too few spatial and temporal collocated matches at wind speed greater than 17ms-1. We are limited in our ability to perform the adjustments required for intercallibration because when comparing visual winds to scatterometer winds the necessary wind speed observations are rare and small in magnitude.
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Date Issued: 2016
Identifier: FSU_2016SP_Li_fsu_0071N_13246
Format: Thesis

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