Search results

Title: Classification of Rain Clouds Based on the Relationship between Microwave Emission and Scattering Signals.
Creator: Li, Jiangmei, Liu, Guosheng, Misra, Vasubandhu, Wing, Allison A., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
Abstract/Description: In this thesis, we introduce a new approach to classify rain clouds based on the relationship between the emission signal and scattering signal derived from microwave brightness temperature data. Two parameters are used as indicators of emission signal and scattering signal respectively: one is the polarization difference (D) at 19 GHz, and the other one is the polarization-corrected temperature (PCT) at high-frequencies channels. D is related to the emission of liquid hydrometeors, and PCT...
Show moreIn this thesis, we introduce a new approach to classify rain clouds based on the relationship between the emission signal and scattering signal derived from microwave brightness temperature data. Two parameters are used as indicators of emission signal and scattering signal respectively: one is the polarization difference (D) at 19 GHz, and the other one is the polarization-corrected temperature (PCT) at high-frequencies channels. D is related to the emission of liquid hydrometeors, and PCT mainly reflects the brightness temperature depression due to the scattering by ice particles. Both D and PCT decrease with increasing precipitation rate. Therefore, certain combinations of D and PCT can be regarded as the representatives of cloud hydrometeor structures. Based on the D-PCT relationship investigated in this study, we classified the observed rain clouds into five categories—non-precipitating, light-precipitating, liquid-dominant precipitating, well-mixed precipitating, and ice-dominant precipitating clouds. We verified the results of the classification of different precipitation cases over tropical regions. For both the hurricane and front cases, the results show that the distributions of categorized cloud pixels can reflect the horizontal structure of the weather systems. The monthly gridded mean frequencies of categorized precipitating clouds are used to analyze the relationship between the seasonal and interannual cycles of tropical precipitation and clouds’ hydrometeor components. Moreover, the results indicated that in an annual cycle or an ENSO cycle, when the local precipitation frequencies increase, the occurrence frequencies of all kinds of rain clouds will increase. However, among those precipitating systems, the proportions of ice-dominant and well-mixed clouds increases while that of water-dominant clouds decrease as the local precipitation increases. Anomalies of the opposite sign tend to accompany the decreasing precipitations situations. Overall, the classification method proves to be useful to extract objective information from observed emission and scattering signals. Since clouds have always been signs of the weather systems, the long-term variances of global distribution and characteristics of rain clouds are as an aspect of cloud climatology. Moreover, the categorization of precipitation types can be useful in developing the best retrieval algorithm of rain rate for a specific cloud type. Additionally, the information about cloud types can be used to improve our understanding of cloud processes and to increase the accuracy of weather and climate models.
Show less
Date Issued: 2019
Identifier: 2019_Spring_Li_fsu_0071N_15013
Format: Thesis

Title: Describing the Onset and Demise of the Australian Monsoon.
Creator: Uehling, John Edward, Misra, Vasubandhu, Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric...
Show moreUehling, John Edward, Misra, Vasubandhu, Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: A comprehensive rainfall-based index of the Australian monsoon is created. This index is based on methodology previously used on the Indian subcontinent for determining the seasonality of the Indian monsoon. In order to create the Australian monsoon index, only rainfall data is used, which even over the sparsely populated areas of northern Australia is available dating back over 100 years (to 1901). The methodology for calculating the Australian monsoon index has been shown to be robust and...
Show moreA comprehensive rainfall-based index of the Australian monsoon is created. This index is based on methodology previously used on the Indian subcontinent for determining the seasonality of the Indian monsoon. In order to create the Australian monsoon index, only rainfall data is used, which even over the sparsely populated areas of northern Australia is available dating back over 100 years (to 1901). The methodology for calculating the Australian monsoon index has been shown to be robust and not susceptible to false onsets. The Australian monsoon index objectively captures the onset date, the demise date, and the total seasonal rainfall for each monsoon season. This new index was then compared to various atmospheric dynamic and thermodynamic variables to see if the index was reflective of the broader seasonal atmospheric changes associated with the monsoon. The Australian monsoon index introduced in this study is found to be consistent with the meridional advancement of the precipitable water south of the equator and over the Australian land mass as the monsoon season begins. Atmospheric dynamics related to the low-level wind data shows a pronounced wind shift across the region corresponding to the onset and the demise of the monsoon based on the rainfall index. The examination of linear trends show that the length of the season has gotten longer and wetter, with earlier onsets and later demises since the beginning of the 20th century. One final aspect of the monsoon that is investigated is the interannual variability of the monsoon and how the El Niño-Southern Oscillation (ENSO) impacts the onset, demise, length of season, and total rainfall of the Australian monsoon. It is observed that warm or cold ENSO events are associated with shorter or longer Australian monsoon season, respectively. Similarly, these warm or cold ENSO events are associated with drier or wetter seasonal rainfall anomalies of the Australian monsoon, respectively.
Show less
Date Issued: 2019
Identifier: 2019_Summer_Uehling_fsu_0071N_15438
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
Show less
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.
Show less
Date Issued: 2019
Identifier: 2019_Summer_Yan_fsu_0071E_15321
Format: Thesis

Title: Hurricane Boundary Layer Structure during Intensity Change: An Observational and Numerical Analysis.
Creator: Ahern, Kyle K. (Kyle Kevin), Bourassa, Mark Allan, Hart, Robert E. (Robert Edward), Harper, Kristine, Fuelberg, Henry E., Misra, Vasubandhu, Chagnon, Jeffrey M., Florida State...
Show moreAhern, Kyle K. (Kyle Kevin), Bourassa, Mark Allan, Hart, Robert E. (Robert Edward), Harper, Kristine, Fuelberg, Henry E., Misra, Vasubandhu, Chagnon, Jeffrey M., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: A combination of observational and numerical analyses is used to investigate hurricane boundary layer (BL) structure in the context of intensity change. These analyses refer to hurricanes in three modes of intensity change: intensifying (IN), steady-state (SS), and weakening (WE). Observations from global positioning system (GPS) dropwindsondes launched in Atlantic tropical cyclones between 1998 and 2015 are collected for compositing based on intensity change. After quality control and...
Show moreA combination of observational and numerical analyses is used to investigate hurricane boundary layer (BL) structure in the context of intensity change. These analyses refer to hurricanes in three modes of intensity change: intensifying (IN), steady-state (SS), and weakening (WE). Observations from global positioning system (GPS) dropwindsondes launched in Atlantic tropical cyclones between 1998 and 2015 are collected for compositing based on intensity change. After quality control and sorting, 3,091 dropwindsondes were composited---1,086 were released into IN hurricanes, 1,042 were released during WE phases, and the remaining 963 releases were associated with steady-state storms. In non-intensifying hurricanes, lower-tropospheric tangential winds were stronger than IN storms outside the radius of maximum winds (RMW), which suggests greater inertial stability I² outside the RMW in non-intensifying hurricanes. The BL radial inflow is of similar thickness across the three composites, and all composite groups have an inflow maximum situated at the RMW. Non-intensifying hurricanes are associated with stronger near-surface inflow outside the eyewall region, which implies more frictionally forced ascent out of the BL at radii outside the RMW. At greater radii, inflow layer Θₑ is relatively low in the WE composite, suggesting enhanced subsidence or downdrafts at those radii. High-resolution numerical case studies of Hurricane Irma in 2017 and Hurricane Earl in 2010 are used to check results found in the composite analysis and highlight BL azimuthal structure. The Weather Research and Forecasting Model for Advanced Research (WRF-ARW) is employed for these full-physics simulations. Irma's strong tangential winds were relatively confined to the RMW, leading to weak I² outside the eyewall. Aside from land interactions, Irma tended to steadily intensify, with an inflow maximum at the RMW and BL ascent isolated inward of the RMW. A brief WE period in Irma was associated with shear- and motion-induced asymmetry, whereby drier air was able to descend into the BL inflow near the RMW. Hurricane Earl had a broader tangential wind field, with high I² outside the eyewall. Earl's strong BL inflow spread over a large radial band, which was associated with widespread BL convergence and shallow ascent outside the RMW. During a prolonged and progressive decay in Earl's intensity, two regions of BL convergence became apparent: one inward of the RMW, and the other well outside the RMW. Descent of low-enthalpy air into the BL near the RMW occurred during Earl's WE phases. Despite shear and storm motion of comparable magnitude to Irma, asymmetries were more pronounced in Earl's BL. Earl's decline in intensity was also associated with strong low-level outflow in the upshear-right quadrant, which may have led to kinematic and thermodynamic evolution that promoted an outer region of BL convergence, as well as an inner-eyewall collapse and coincident secondary eyewall formation.
Show less
Date Issued: 2019
Identifier: 2019_Fall_Ahern_fsu_0071E_15454
Format: Thesis

Title: The Origin of the North Atlantic Clod Blob Revisited.
Creator: Bhatrasataponkul, Tachanat, Bourassa, Mark Allan, Elsner, James B., Clarke, Allan J., Dewar, William K., Speer, Kevin G., Florida State University, College of Arts and Sciences,...
Show moreBhatrasataponkul, Tachanat, Bourassa, Mark Allan, Elsner, James B., Clarke, Allan J., Dewar, William K., Speer, Kevin G., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
Show less
Abstract/Description: The cold blob refers to an observationally unprecedented, gyre-scale, record-breaking cold of mean surface temperature over the subpolar North Atlantic. Its anomalous cold feature goes against the rising trend of global mean surface temperature in the context of a warming climate. Observations show that the Atlantic cold blob emerged in early 2014 and can penetrate deeper into the ocean interior beyond 500m depths. A sudden drop in upper ocean heat content is associated with an accumulative...
Show moreThe cold blob refers to an observationally unprecedented, gyre-scale, record-breaking cold of mean surface temperature over the subpolar North Atlantic. Its anomalous cold feature goes against the rising trend of global mean surface temperature in the context of a warming climate. Observations show that the Atlantic cold blob emerged in early 2014 and can penetrate deeper into the ocean interior beyond 500m depths. A sudden drop in upper ocean heat content is associated with an accumulative increase in freshwater content. Prior works pointed out that intense surface forcing during two consecutive winters was a primary driver. We hypothesize that surface forcing alone is insufficient for the cold blob to persist. Our analysis shows, for the first time, that variations in the net surface heat fluxes cannot explain the decline in upper ocean heat content during 2014–2017. Therefore, surface forcing fails to explain the origin of the cold blob. To investigate alternative mechanisms, non-assimilative simulations based on a coupled ocean-sea ice model (GFDL MOM5/SIS1) with two different atmospheric forcings (MERRA2 and ERA-interim) are employed to examine the transports of mass, heat, and freshwater within the cold blob area. Initial diagnosis verified that both model runs can reproduce the cold blob characteristics at similar magnitudes to Argo observations. Model results show a decreasing trend of heat transport at the southern boundary, implying that reduced poleward ocean heat transport likely accounts for the formation and persistence of the cold blob. This cooling signal from the south is accompanied by a freshening signal. Changes in the residual heat fluxes suggest that reduced warming for the subsurface layer at 100–700 m depths apparently occurred since 2006 before turning into enhanced cooling during late 2013. Variations in the residual freshwater fluxes remain positive for the entire past decade and subsequently result in an accumulative surplus of freshwater content in this area. The model run with incorporated Greenland meltwater estimates sheds light on the relative contribution of meltwater advection. To a great extent, Greenland meltwater can amplify the freshening tendency in the subpolar North Atlantic by approximately up to 200% during the present decade. In the long run, upper ocean cooling and freshening would lead to increased stratification and reduced mixing with deeper waters, therefore enhancing the likelihood that the subsurface cold blob persists.
Show less
Date Issued: 2018
Identifier: 2018_Fall_Bhatrasataponkul_fsu_0071E_14875
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
Show less
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.
Show less
Date Issued: 2018
Identifier: 2018_Fall_DiCatarina_fsu_0071N_14783
Format: Thesis

Title: A Geography of Tornado Casualties in the United States.
Creator: Fricker, Tyler, Elsner, James B., Hart, Robert E. (Robert Edward), Mesev, Victor, McCreary, Tyler, Florida State University, College of Social Sciences and Public Policy,...
Show moreFricker, Tyler, Elsner, James B., Hart, Robert E. (Robert Edward), Mesev, Victor, McCreary, Tyler, Florida State University, College of Social Sciences and Public Policy, Department of Geography
Show less
Abstract/Description: This dissertation includes a series of chapters that evaluate tornado casualties in a spatial, historical, and social context. Previous studies have identified the location of tornado casualties using the best available data and assessed the link between social, economic, and demographic factors to the number of tornado casualties. This research builds and deviates from earlier research through the use of a number of geographical methods. More specifically, the research presented here aims to...
Show moreThis dissertation includes a series of chapters that evaluate tornado casualties in a spatial, historical, and social context. Previous studies have identified the location of tornado casualties using the best available data and assessed the link between social, economic, and demographic factors to the number of tornado casualties. This research builds and deviates from earlier research through the use of a number of geographical methods. More specifically, the research presented here aims to (1) predict the rate of tornado casualties as a function of tornado strength and population, (2) provide a dasymetric method to estimate socioeconomic and demographic variables at the tornado-level, and (3) define and identify unusually devastating tornadoes---those that cause significantly more casualties than some expected rate---which in turn recognizes vulnerable communities throughout the United States. Tornado records are fit to two different statistical models containing estimates of energy dissipation and population density: (1) an additive model and (2) an interactive model. Tornado energy dissipation is estimated through a physical model, which expresses the strength of a tornado. Results show that, for the additive model, a doubling in population increases the casualty rate by 21% [(17, 24)%, 95% credible interval] and a doubling in energy dissipation increases the casualty rate by 33% [(30, 35)%, 95% credible interval]. Results also show that, for the interactive model, the percentage increase in casualties with increasing energy dissipation increases with population density, and the percentage increase in casualties with increasing population density increases with energy dissipation. Estimates of socioeconomic and demographic variables at the tornado-level are found through dasymetric calculations that can be analyzed independently or in combination with other attributes in the historical record. These estimates are validated using known fatalities and actual tornado paths found within the National Weather Service's Damage Assessment Toolkit. Results show large correlation between estimated and observed fatalities exceeding .93 for four distinct age groups and .99 for sex. Unusually devastating tornadoes are defined and identified through a model for tornado casualties that builds on the interactive model, but includes estimates of socioeconomic and demographic variables. Results show that unusually devastating tornadoes can occur anywhere in the United States, but appear more consistently over parts of the rural South. By identifying clusters of unusually devastating tornadoes, individual communities can be further examined. For example, three examples of unusually devastating tornadoes include: (1) the 1998 Spencer, South Dakota tornado, (2) the 2000 and 2003 Camilla, Georgia tornadoes, and (3) the 2015 Garland-Rowlett, Texas tornado. Each of these cities have their own socioeconomic and demographic profiles, yet were hit by tornadoes that caused more casualties than expected given a model for tornado casualties. The results provide a substantial improvement in the quantitative and geographic understanding of tornado casualties across the United States. They also set the stage for future critiques of the systems in place that drive human vulnerability to tornadoes. In this sense, the results highlight the need for additional work to be devoted to understanding the tornado casualty problem. The methods presented here supply a foundation for future studies that evaluate changes in the tornado casualty landscape and make sense of the challenges many communities face with regard to the tornado hazard.
Show less
Date Issued: 2018
Identifier: 2019_Spring_Fricker_fsu_0071E_14975
Format: Thesis

Title: Ice Cloud Properties and Their Radiative Effects: Global Observations and Modeling.
Creator: Hong, Yulan, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Chicken, Eric, Ellingson, R. G., Cai, Ming, Wu, Zhaohua, Florida State University, College of...
Show moreHong, Yulan, Liu, Guosheng (Professor of Earth, Ocean and Atmospheric Science), Chicken, Eric, Ellingson, R. G., Cai, Ming, Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Ice clouds are crucial to the Earth's radiation balance. They cool the Earth-atmosphere system by reflecting solar radiation back to space and warm it by blocking outgoing thermal radiation. However, there is a lack of an observation-based climatology of ice cloud properties and their radiative effects. Two active sensors, the CloudSat radar and the CALIPSO lidar, for the first time provide vertically resolved ice cloud data on a global scale. Using synergistic signals of these two sensors,...
Show moreIce clouds are crucial to the Earth's radiation balance. They cool the Earth-atmosphere system by reflecting solar radiation back to space and warm it by blocking outgoing thermal radiation. However, there is a lack of an observation-based climatology of ice cloud properties and their radiative effects. Two active sensors, the CloudSat radar and the CALIPSO lidar, for the first time provide vertically resolved ice cloud data on a global scale. Using synergistic signals of these two sensors, it is possible to obtain both optically thin and thick ice clouds as the radar excels in probing thick clouds while the lidar is better to detect the thin ones. First, based on the CloudSat radar and CALIPSO lidar measurements, we have derived a climatology of ice cloud properties. Ice clouds cover around 50% of the Earth surface, and their global-mean optical depth, ice water path, and effective radius are approximately 2 (unitless), 109 g m⁻² and 48 μm, respectively. Ice cloud occurrence frequency not only depends on regions and seasons, but also on the types of ice clouds as defined by optical depth (τ) values. Optically thin ice clouds (τ < 3) are most frequently observed in the tropics around 15 km and in the midlatitudes below 5 km, while the thicker clouds (τ > 3) occur frequently in the tropical convective areas and along the midlatitude storm tracks. Using ice retrievals derived from combined radar-lidar measurements, we conducted radiative transfer modeling to study ice cloud radiative effects. The combined effects of ice clouds warm the earth-atmosphere system by approximately 5 W m⁻², contributed by a longwave warming effect of about 21.8 W m⁻² and a shortwave cooling effect of approximately -16.7 W m⁻². Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, and the net warming effect occurs year-round in the tropics (∼ 10 W m⁻² ). Ice cloud optical depth is shown to be an important factor in determining the sign and magnitude of the net radiative effect. On a global average, ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. Optically thin and high ice clouds cause strong heating in the tropical upper troposphere, while outside the tropics, mixed-phase clouds cause strong cooling at lower altitudes (> 5 km). In addition, ice clouds occurring with liquid clouds in the same profile account for about 30% of all observations. These liquid clouds reduce longwave heating rates in ice cloud layers by 0-1 K/day depending on the values of ice cloud optical depth and regions. This research for the first time provides a clear picture on the global distribution of ice clouds with a wide range of optical depth. Through radiative transfer modeling, we have gained better knowledge on ice cloud radiative effects and their dependence on ice cloud properties. These results not only improve our understanding of the interaction between clouds and climate, but also provide observational basis to evaluate climate models.
Show less
Date Issued: 2017
Identifier: FSU_SUMMER2017_Hong_fsu_0071E_13993
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
Show less
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.
Show less
Date Issued: 2017
Identifier: FSU_2017SP_Sims_fsu_0071E_13720
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
Show less
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.
Show less
Date Issued: 2016
Identifier: FSU_2016SP_Barton_fsu_0071E_13099
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
Show less
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.
Show less
Date Issued: 2016
Identifier: FSU_FA2016_Allison_fsu_0071N_13632
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
Show less
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.
Show less
Date Issued: 2016
Identifier: FSU_2016SU_Nag_fsu_0071E_13367
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
Show less
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.
Show less
Date Issued: 2016
Identifier: FSU_2016SP_Hazelton_fsu_0071E_13072
Format: Thesis

Title: Ozone Deposition Degrades Water Use Efficiency Across Multiple Ecosystems.
Creator: Ducker, Jason Alexander, Holmes, Christopher D., Pau, Stephanie, Misra, Vasubandhu, Ahlquist, Jon E., Florida State University, College of Arts and Sciences, Department of Earth...
Show moreDucker, Jason Alexander, Holmes, Christopher D., Pau, Stephanie, Misra, Vasubandhu, Ahlquist, Jon E., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Atmosphere-biosphere exchange plays a key role in the global cycles of water and carbon. Air pollution can alter these processes and induce climate perturbations and feedbacks. Surface ozone (O3) is an air pollutant and greenhouse gas that is toxic to plants, reducing their growth and ability to regulate water loss. Past controlled experiments have shown that O3 degrades a plant's water-use efficiency (WUE), which is the ratio of carbon uptake in photosynthesis to water loss in transpiration....
Show moreAtmosphere-biosphere exchange plays a key role in the global cycles of water and carbon. Air pollution can alter these processes and induce climate perturbations and feedbacks. Surface ozone (O3) is an air pollutant and greenhouse gas that is toxic to plants, reducing their growth and ability to regulate water loss. Past controlled experiments have shown that O3 degrades a plant's water-use efficiency (WUE), which is the ratio of carbon uptake in photosynthesis to water loss in transpiration. This has potentially significant implications for terrestrial water cycle and precipitation, but no studies have evaluated the O3 effect on WUE in complete ecosystems. We aim to quantify the impact of O3 on WUE across a wide array of ecosystems. Meteorological and biological data was obtained from 23 FLUXNET flux tower sites, which use the eddy covariance method to derive hourly fluxes of carbon dioxide (CO2), water vapor (H2O), and O3 between the atmosphere and ecosystem. Across a broad range of sites, we find a significant negative relationship between daily anomalies of stomatal O3 flux (FS, O3) and WUE that explains 1-3% of WUE variability. The largest impacts occur in locations and species with high stomatal conductance, such as broadleaf forests, humid climates, or irrigated crops, rather than where surface O3 concentrations are highest. Past long-term studies have also found similar O3 impacts (1-3%) on WUE, indicating a consistent response across a pool species and ecosystems.
Show less
Date Issued: 2016
Identifier: FSU_2016SP_Ducker_fsu_0071N_13195
Format: Thesis

Title: Local Cooling Despite Global Warming.
Creator: Girihagama, Lakshika Nilmini Kumari, Nof, Doron, Tam, Christopher K. W., Bourassa, Mark Allan, Clarke, Allan J., Sura, Philip, Ewald, Brian D., Florida State University, College...
Show moreGirihagama, Lakshika Nilmini Kumari, Nof, Doron, Tam, Christopher K. W., Bourassa, Mark Allan, Clarke, Allan J., Sura, Philip, Ewald, Brian D., Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
Show less
Abstract/Description: How much warmer is the ocean surface than the atmosphere directly above it? Part 1 of the present study offers a means to quantify this temperature difference using a nonlinear one-dimensional global energy balance coupled ocean–atmosphere model ("Aqua Planet"). The significance of our model, which is of intermediate complexity, is its ability to obtain an analytical solution for the global average temperatures. Preliminary results show that, for the present climate, global mean ocean...
Show moreHow much warmer is the ocean surface than the atmosphere directly above it? Part 1 of the present study offers a means to quantify this temperature difference using a nonlinear one-dimensional global energy balance coupled ocean–atmosphere model ("Aqua Planet"). The significance of our model, which is of intermediate complexity, is its ability to obtain an analytical solution for the global average temperatures. Preliminary results show that, for the present climate, global mean ocean temperature is 291.1 K whereas surface atmospheric temperature is 287.4 K. Thus, the surface ocean is 3.7 K warmer than the atmosphere above it. Temporal perturbation of the global mean solution obtained for "Aqua Planet" showed a stable system. Oscillation amplitude of the atmospheric temperature anomaly is greater in magnitude to those found in the ocean. There is a phase shift (a lag in the ocean), which is caused by oceanic thermal inertia. Climate feedbacks due to selected climate parameters such as incoming radiation, cloud cover, and CO2 are discussed. Warming obtained with our model compares with Intergovernmental Panel on Climate Change's (IPCC) estimations. Application of our model to local regions illuminates the importance of evaporative cooling in determining derived air-sea temperature offsets, where an increase in the latter increases the systems overall sensitivity to evaporative cooling. In part 2, we wish to answer the fairly complicated question of whether global warming and an increased freshwater flux cause Northern Hemispheric warming or cooling. Starting from the assumption of the ocean as the primary source of variability in the Northern hemispheric ocean–atmosphere coupled system, we employed a simple non–linear one–dimensional coupled ocean–atmosphere model similar to the "Aqua Planet" model but with additional advective heat transports. The simplicity of this model allows us to analytically predict the evolution of many dynamical variables of interest such as, the strength of the Atlantic Meridional overturning circulation (AMOC), temperatures of the ocean and atmosphere, mass transports, salinity, and ocean–atmosphere heat fluxes. Model results show that a reduced AMOC transport due to an increased freshwater flux causes cooling in both the atmosphere and ocean in the North Atlantic (NA) deep–water formation region. Cooling in both the ocean and atmosphere can cause a reduction of the ocean–atmosphere temperature difference, which in turn reduces heat fluxes in both the ocean and atmosphere. For present day climate parameters, the calculated critical freshwater flux needed to arrest AMOC is 0.14 Sv. Assuming a constant atmospheric zonal flow, there is both minimal reduction in the AMOC strength, as well as minimal warming of the ocean and atmosphere. This model provides a conceptual framework for a dynamically sound response of the ocean and atmosphere to AMOC variability as a function of increased freshwater flux. The results are qualitatively consistent with numerous realistic coupled numerical models of varying complexity.
Show less
Date Issued: 2015
Identifier: FSU_2015fall_Girihagama_fsu_0071E_12927
Format: Thesis

Title: WRF Nested Large-Eddy Simulations of Deep Convection during SEAC4RS.
Creator: Heath, Nicholas Kyle, Fuelberg, Henry E., Wiedenhöver, Ingo, Hart, Robert E. (Robert Edward), Bourassa, Mark Allan, Misra, Vasubandhu, Turk, Francis J., Florida State University...
Show moreHeath, Nicholas Kyle, Fuelberg, Henry E., Wiedenhöver, Ingo, Hart, Robert E. (Robert Edward), Bourassa, Mark Allan, Misra, Vasubandhu, Turk, Francis J., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Deep convection is an important component of atmospheric circulations that affects many aspects of weather and climate. Therefore, improved understanding and realistic simulations of deep convection are critical to both operational and climate forecasts. Large-eddy simulations (LESs) often are used with observations to enhance understanding of convective processes. This study develops and evaluates a nested-LES method using the Weather Research and Forecasting (WRF) model. Our goal is to...
Show moreDeep convection is an important component of atmospheric circulations that affects many aspects of weather and climate. Therefore, improved understanding and realistic simulations of deep convection are critical to both operational and climate forecasts. Large-eddy simulations (LESs) often are used with observations to enhance understanding of convective processes. This study develops and evaluates a nested-LES method using the Weather Research and Forecasting (WRF) model. Our goal is to evaluate the extent to which the WRF nested-LES approach is useful for studying deep convection during a real-world case. The method was applied on 2 September 2013, a day of continental convection having a robust set of ground and airborne data available for evaluation. A three domain mesoscale WRF simulation is run first. Then, the finest mesoscale output (1.35 km grid length) is used to separately drive nested-LES domains with grid lengths of 450 and 150 m. Results reveal that the nested-LES approach reasonably simulates a broad spectrum of observations, from reflectivity distributions to vertical velocity profiles, during the study period. However, reducing the grid spacing does not necessarily improve results for our case, with the 450 m simulation outperforming the 150 m version. We find that simulated updrafts in the 150 m simulation are too narrow to overcome the negative effects of entrainment, thereby generating convection that is weaker than observed. Increasing the sub-grid mixing length in the 150 m simulation leads to deeper, more realistic convection, but comes at the expense of delaying the onset of the convection. Overall, results show that both the 450 m and 150 m simulations are influenced considerably by the choice of sub-grid mixing length used in the LES turbulence closure. Finally, the simulations and observations are used to study the processes forcing strong midlevel cloud-edge downdrafts that were observed on 2 September. Results suggest that these downdrafts are forced by evaporative cooling due to mixing near cloud edge and by vertical perturbation pressure gradient forces acting to restore mass continuity around neighboring updrafts. We conclude that the WRF nested-LES approach provides an effective method for studying deep convection for our real-world case. The method can be used to provide insight into physical processes that are important to understanding observations. The WRF nested-LES approach could be adapted for other case studies in which high-resolution observations are available for validation.
Show less
Date Issued: 2015
Identifier: FSU_2015fall_Heath_fsu_0071E_12917
Format: Thesis

Title: Examining Shifts in Warm-Season Near-Surface Moisture Trends in Florida.
Creator: Swearingen, Aaron D., Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: Warm-season (1 June–31 August) near-surface moisture trends have been examined across Florida. Data was used from 86 National Weather Service cooperative stations, 24 NWS first-order stations, and the European Centre for Medium-Range Weather Forecasts' ERA-Interim satellite reanalysis. Seventy-five out of eighty-six NWS cooperative stations depicted high counts of maximum low temperature records being set or broken since 1990. Twenty-four NWS hourly stations were used in conjunction with the...
Show moreWarm-season (1 June–31 August) near-surface moisture trends have been examined across Florida. Data was used from 86 National Weather Service cooperative stations, 24 NWS first-order stations, and the European Centre for Medium-Range Weather Forecasts' ERA-Interim satellite reanalysis. Seventy-five out of eighty-six NWS cooperative stations depicted high counts of maximum low temperature records being set or broken since 1990. Twenty-four NWS hourly stations were used in conjunction with the Pettitt test to calculate a change point of 1990 over a 40-year period (1973–2012). Using the Pettitt results, a significant amount of NWS first-order stations depicted a rise in both early morning temperatures and dew points (Td) since 1990. A rise in total column water vapor (TCWV) was detected through the ERA-Interim reanalysis, indicating a possible increase in mid-level moisture in addition to that near the surface. A reversal in 850 hPa wind patterns and a potential shift in the Azores High were present in the reanalysis as well. An increase in atmospheric moisture levels is present and may be driven by synoptic-scale changes in wind patterns due to a shift in the Azores High.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0528
Format: Thesis

Title: A High Resolution Atmospheric Chemistry Simulation of Hurricane Sandy (2012).
Creator: Freeman, Sean, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: Hurricane Sandy (2012) had one of the greatest economic impacts of any hurricane in United States history. However, its broader scientific impacts, especially its impacts on the chemistry of the upper troposphere and lower stratosphere, have not been documented. This study uses the Weather Research and Forecasting with Chemistry model (WRF-Chem), run at a convective-permitting resolution, to examine the transport of pollutants inside Hurricane Sandy as it made landfall along the Eastern...
Show moreHurricane Sandy (2012) had one of the greatest economic impacts of any hurricane in United States history. However, its broader scientific impacts, especially its impacts on the chemistry of the upper troposphere and lower stratosphere, have not been documented. This study uses the Weather Research and Forecasting with Chemistry model (WRF-Chem), run at a convective-permitting resolution, to examine the transport of pollutants inside Hurricane Sandy as it made landfall along the Eastern Seaboard. Although several pollutants were examined, the concentrations of CO throughout the atmosphere and the transport of CO from sources along the coast in Hurricane Sandy's convective region were primary focus. A forward-trajectory analysis also was performed using the high-resolution WRF-Chem data as input to the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT). The results of this high-resolution chemical and meteorological simulation will be presented with a focus on transport to the upper troposphere and lower stratosphere. To our knowledge, such high-resolution chemical and meteorological simulations of tropical cyclones have not been reported in the previous literature.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0477
Format: Thesis

Title: An Analysis of the Extratropical Flow Response to Recurving Atlantic Tropical Cyclones.
Creator: Brannan, Allison, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: There is a significant frequency of Atlantic tropical cyclones that complete extratropical transition and recurve in the mid-latitudes. Using a climatological approach, this study will analyze the extratropical flow response to recurving Atlantic tropical cyclones and compare the results to those from the Western North Pacific, as examined by Archambault et al. (2013). This investigation includes 54 recurving Atlantic tropical cyclones occurring between 2007 and 2013. The extratropical flow...
Show moreThere is a significant frequency of Atlantic tropical cyclones that complete extratropical transition and recurve in the mid-latitudes. Using a climatological approach, this study will analyze the extratropical flow response to recurving Atlantic tropical cyclones and compare the results to those from the Western North Pacific, as examined by Archambault et al. (2013). This investigation includes 54 recurving Atlantic tropical cyclones occurring between 2007 and 2013. The extratropical flow response will be quantified using potential vorticity. Characteristics of tropical cyclones, the extratropical jet stream, and the dynamical "phasing" of their interaction will be examined to determine the features that lead to significantly amplified extratropical flow. Results show the extratropical flow to be insensitive to the wind speed, latitude, and month of recurvature. However, there is an association between low mean sea level pressure and a larger amplification of flow. Finally, tropical cyclones recurving on the east side of the nearest trough are shown to have "favorable phasing," which yields amplification of the extratropical flow.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0538
Format: Thesis

Title: Investigating Relationships Between Rising Temperatures and Heavy Rainfall Events in the Southeastern U.S. Using Analog Methods.
Creator: Zuromski, Lauren, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: This study examines how extreme precipitation influences temperatures, and how temperature extremes influence precipitation in the Southeastern U.S., seasonally, using observational data. For the precipitation influencing temperature approach, three precipitation regimes are created (wet, dry, and neutral) to observe possible shifts in the distributions of seasonal average daily maximum and minimum temperatures based on precipitation extremes. Similarly, for the temperature influencing...
Show moreThis study examines how extreme precipitation influences temperatures, and how temperature extremes influence precipitation in the Southeastern U.S., seasonally, using observational data. For the precipitation influencing temperature approach, three precipitation regimes are created (wet, dry, and neutral) to observe possible shifts in the distributions of seasonal average daily maximum and minimum temperatures based on precipitation extremes. Similarly, for the temperature influencing precipitation, three temperature regimes are created (warm, cool, and neutral), to observe how the frequency of rainfall events of 1.00" or more shifts in each temperature regime. For the precipitation influencing temperature approach, most notably, it is found that in summer, spring, and fall, in a wet precipitation regime, the maximum temperatures are typically warmer (cooler) than the average maximum temperatures in a neutral regime; the opposite pattern is observed for winter. It is also found that these temperature distributions do not shift in a uniform way across the Southeast, though several regional continuities exist. For the temperature influencing precipitation approach, it is found that spring, summer, and winter show the largest differences in the frequency of rainfall events of 1.00" or more between the cool and warm temperature regimes. This study also examines five case study stations in the Southeast to observe regional nuances in temperature and precipitation patterns.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0511
Format: Thesis

Title: IC to CG Lightning Relationships over the Tallahassee CWA.
Creator: Jackson, Karly M., Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: The formation of and the relationship between intra-cloud (IC) and cloud-to-ground (CG) lightning flashes have not been thoroughly studied. Understanding how these flash types interact in different types of thunderstorms can lead to a better understanding of lightning characteristics and how these characteristics can be applied to operational forecasting practices. Results of this study show that the IC:CG ratio varies greatly each day throughout the summer season over the County Warning Area...
Show moreThe formation of and the relationship between intra-cloud (IC) and cloud-to-ground (CG) lightning flashes have not been thoroughly studied. Understanding how these flash types interact in different types of thunderstorms can lead to a better understanding of lightning characteristics and how these characteristics can be applied to operational forecasting practices. Results of this study show that the IC:CG ratio varies greatly each day throughout the summer season over the County Warning Area (CWA) of the Tallahassee National Weather Service Forecast Office. The summer season is dominated by daily thunderstorms that form due to sea breeze fronts and their resulting outflow boundaries. Eleven case study storms reveal how IC and CG flash counts and rates in non-severe thunderstorms differ from those of severe storms such as those examined by Williams et al. (1999). Results of the present study reveal that the timing of CG lightning and the frequency of its strikes differ from those of severe storms. This is most likely due to severe storms producing stronger updrafts for longer periods of time than those of non-severe storms. The IC:CG ratios varied greatly among these case studies indicating that further studies must be done to determine a statistically significant understanding of how flash rates change and how the relationship between IC and CG flashes relate to the ratios they produce.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0552
Format: Thesis

Title: Remotely Sensed Validation of Numerical Weather Prediction Estimates of Wind Speed Near Tropical Cyclones.
Creator: Dacey, Connor, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: This study examined the tendencies of the European Center for Medium-Range Weather Forecasting Ensemble Prediction System (ECMWF-EPS) control forecast of wind speeds near two rapidly intensifying tropical cyclones (TCs) in the Indian Ocean. The ECMWF-EPS control forecasts were compared with the Advanced Scatterometer (ASCAT) wind speed measurements, which were considered comparison and "truth" data for this study. In total, 6 days of model forecast and ASCAT data were collected and analyzed...
Show moreThis study examined the tendencies of the European Center for Medium-Range Weather Forecasting Ensemble Prediction System (ECMWF-EPS) control forecast of wind speeds near two rapidly intensifying tropical cyclones (TCs) in the Indian Ocean. The ECMWF-EPS control forecasts were compared with the Advanced Scatterometer (ASCAT) wind speed measurements, which were considered comparison and "truth" data for this study. In total, 6 days of model forecast and ASCAT data were collected and analyzed for severe tropical cyclones Phet and Giri. Differences in the magnitudes of the wind speeds near the TCs were calculated. From these, areas can be seen in which the ECMWF-EPS control over-forecasted and under-forecasted the wind speeds. These results also help explain how the model tendencies changed throughout the lifespan of the TCs. Overall, wind speed errors were greatly associated with errors in storm location, storm shape, and storm size. No exact conclusion about the tendencies of the ECMWF-EPS control forecasts could be made due to a lack of patterns or clear biases associated with the wind speed difference results. A more in-depth study must be completed to further comment on specific tendencies of the model. Nevertheless, this study could begin the investigation into how to improve wind speed forecasts for TCs in the Indian Ocean in an effort to better save life and property in the future.
Show less
Date Issued: 2015
Identifier: FSU_migr_uhm-0548
Format: Thesis

Title: Quantification of Stokes Drift as a Mechanism for Surface Oil Advection in the Gulf of Mexico during the Deepwater Horizon Oil Spill.
Creator: Clark, Matthew, Bourassa, Mark Allan, Chassignet, Eric P., Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean,...
Show moreClark, Matthew, Bourassa, Mark Allan, Chassignet, Eric P., Hart, Robert E. (Robert Edward), Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Wave-driven transport, also known as Stokes drift, is the motion of a particle due to the orbital motion induced by a passing wave. This orbital motion does not form closed loops, leading to a net displacement over a single wave period. Stokes drift has previously been qualitatively shown to be a factor in ocean surface particle transport, with most studies focused exclusively in near-shore regions. However, Stokes drift has never been quantified beyond theoretical studies and case studies...
Show moreWave-driven transport, also known as Stokes drift, is the motion of a particle due to the orbital motion induced by a passing wave. This orbital motion does not form closed loops, leading to a net displacement over a single wave period. Stokes drift has previously been qualitatively shown to be a factor in ocean surface particle transport, with most studies focused exclusively in near-shore regions. However, Stokes drift has never been quantified beyond theoretical studies and case studies limited to small regions. Here, Stokes drift is calculated directly from Wavewatch III model data in the Gulf of Mexico for April-July 2010. Its magnitudes are compared between deep and shelf water areas, and against the magnitudes of surface currents and parameterized wind drift. These comparisons are also made specifically for the time period surrounding the passage of Hurricane Alex through the southwestern Gulf of Mexico. While there is not a major difference between the absolute magnitudes of Stokes drift in shelf vs. deep water areas or when compared to wind drift, Stokes drift is larger in shelf water areas relative to surface currents than in deep water. During Hurricane Alex, Stokes drift magnitudes were much larger in the immediate area of the storm, while in the oil spill area there was little change until after the storm was out of the Gulf, at which time swell had propagated into the region, increasing Stokes drift magnitudes.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9576
Format: Thesis

Title: Investigating the Potentially Untapped Predictability of Tropical Cyclone Genesis in Operational Global Models.
Creator: Halperin, Daniel J., Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Harper, Kristine, Chagnon, Jeffrey M., Liu, Guosheng, Florida State University, College of Arts and...
Show moreHalperin, Daniel J., Fuelberg, Henry E., Hart, Robert E. (Robert Edward), Harper, Kristine, Chagnon, Jeffrey M., Liu, Guosheng, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: There is an operational need for accurate tropical cyclone (TC) genesis forecasts. Global numerical models are an important genesis guidance tool, but each model has biases. Further, the interpretation of when genesis occurs in a model forecast field can be subjective. Thus, this study seeks to create an automated, objective, statistical-dynamical TC genesis guidance tool for the North Atlantic and eastern North Pacific basins based on output from the CMC, GFS, and UKMET global models....
Show moreThere is an operational need for accurate tropical cyclone (TC) genesis forecasts. Global numerical models are an important genesis guidance tool, but each model has biases. Further, the interpretation of when genesis occurs in a model forecast field can be subjective. Thus, this study seeks to create an automated, objective, statistical-dynamical TC genesis guidance tool for the North Atlantic and eastern North Pacific basins based on output from the CMC, GFS, and UKMET global models. Another goal is to determine how well important genesis processes in global models agree with those theoretically proposed. This research also attempts to identify the characteristics of successful and failed genesis forecasts. First, historical global model forecasts of TC genesis over the past decade are verified. Using this genesis forecast archive, univariable logistic regression equations are created to reveal the statistical relationships between relevant variables and genesis probability. These statistical relationships are compared to theoretical relationships between atmospheric variables and TC genesis. Results show several expected and counterintuitive statistical relationships, with some disagreement among the models. Multiple logistic regression equations then are developed to provide probabilistic genesis forecasts. Separate equations are developed for each global model, basin, and forecast window. Additionally, a consensus regression equation is developed. These equations are tested operationally during the 2014 hurricane season. Verification of the independent data indicates generally well-calibrated guidance. Homogeneous comparisons of the consensus regression equation and National Hurricane Center Tropical Weather Outlook genesis probabilities are presented. Case studies and composite analyses are conducted to gain further insight. Case studies from the following categories are selected: (1) African Easterly Wave genesis over the Main Development Region; (2) genesis from stalled frontal boundaries; (3) genesis via tropical transition; and (4) genesis over the Gulf of Mexico. Hit, miss, and false alarm events are compared. Storm centered composite analyses also are constructed to examine differences in the environments between hit and false alarm forecasts. Separate composites are made for the eastern Main Development Region (where the GFS false alarm rate is greatest) and the remainder of the North Atlantic basin. Statistically significant differences between hit and false alarm cases are found for all variables analyzed with various areal extents. Results from the case studies and composite analyses will help guide new predictors to test for inclusion into the multiple logistic regression equations. Additionally, the case study of Sean (2011) suggests that changes to the TC identification algorithm are needed to better detect subtropical to tropical transition. Real-time guidance products based on the logistic regression equations are being evaluated by hurricane specialists at the National Hurricane Center. It is possible that the products will be selected for operational implementation pending further testing and evaluation during 2015.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9607
Format: Thesis

Title: Assessing the Ability of Climate Models to Simulate the Observed Sensitivity of Tropical Cyclone Intensity to Sea Surface Temperature.
Creator: Strazzo, Sarah E., Elsner, James B., Fuelberg, Henry E., Uejio, Christopher K., Zhao, Tingting, Florida State University, College of Social Sciences and Public Policy,...
Show moreStrazzo, Sarah E., Elsner, James B., Fuelberg, Henry E., Uejio, Christopher K., Zhao, Tingting, Florida State University, College of Social Sciences and Public Policy, Department of Geography
Show less
Abstract/Description: This series of studies evaluates the ability of global climate models (GCMs) to simulate the observed relationship between the upper limit of tropical cyclone (TC) intensity and sea surface temperature (SST). Previous studies addressed whether GCMs are capable of reproducing observed TC frequency and intensity distributions. This research builds upon these earlier studies by examining how well GCMs capture physically relevant relationships that are important for understanding the impacts of...
Show moreThis series of studies evaluates the ability of global climate models (GCMs) to simulate the observed relationship between the upper limit of tropical cyclone (TC) intensity and sea surface temperature (SST). Previous studies addressed whether GCMs are capable of reproducing observed TC frequency and intensity distributions. This research builds upon these earlier studies by examining how well GCMs capture physically relevant relationships that are important for understanding the impacts of climate change on TC intensity. The research presented here aims to 1) quantify differences between the observed and simulated sensitivity of TC limiting intensity to SST, and 2) explore possible explanations for any differences that exist. Observed TC data are compared to simulated TCs from four different GCMs---the FSU-COAPS, GFDL-HiRAM, MRI-AGCM, and NCAR-CAM. Model horizontal grid spacing ranges from ~100 km for the FSU-COAPS to ~20 km for the MRI-AGCM. An additional comparison is made for TCs generated through a statistical-deterministic downscaling technique. This research uses a spatial tessellation approach that spatially bins North Atlantic TC and SST data into equal-area hexagon regions. For each region, the statistical upper limit of observed and simulated TC intensity (i.e., limiting intensity) is estimated using extreme value theory. For comparison with the statistical limiting intensity, reanalysis and model field data are employed to approximate observed and simulated potential intensity, respectively. Results reveal that the current suite of GCMs do not capture the observed sensitivity of TC limiting intensity to SST. While a 1° C increase in SST corresponds to a 7.9 +/- 1.19 m/s increase in observed limiting intensity, the same 1° C increase in SST is not associated with a statistically significant increase in simulated TC limiting intensity. This is found to be true both for relatively coarse resolution GCMs that do not generate TCs with intensities exceeding 50 m/s as well as for higher resolution GCMs that are capable of simulating Category 5 hurricanes. Rather than SST, it is found that simulated TC limiting intensity is highly sensitive to 700--400 hPa relative humidity. Conversely, relative humidity does not describe any of the residual variance in observed TC limiting intensity. Therefore, this research suggests that even if a model is able to resolve realistically strong TCs, those simulated TCs may not be governed by the same thermodynamic principles as those that we observe. Although GCMs do not capture the observed sensitivity of limiting intensity to SST, it is shown that the FSU-COAPS model capably reproduces the observed sensitivity of potential intensity to SST. The model generates a thermodynamic environment suitable for the development of strong TCs over the correct portions of the basin, however strong simulated TCs do not develop. This result strongly supports the notion that direct simulation of TC eyewall convection is necessary to accurately represent TC intensity and intensification processes in climate models.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9463
Format: Thesis

Title: Analysis and Prediction of Integrated Kinetic Energy in Atlantic Tropical Cyclones.
Creator: Kozar, Michael E., Misra, Vasubandhu, Ye, Ming, Hart, Robert E. (Robert Edward), Sura, Philip, Clarke, Allan J., Powell, Mark Dillon, Florida State University, College of Arts...
Show moreKozar, Michael E., Misra, Vasubandhu, Ye, Ming, Hart, Robert E. (Robert Edward), Sura, Philip, Clarke, Allan J., Powell, Mark Dillon, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Integrated kinetic energy (IKE) is a recently developed metric that approximates the destructive potential of a tropical cyclone by assessing the size and strength of its wind field. Despite the potential usefulness of the IKE metric, there are few, if any, operational tools that are specifically designed to forecast IKE in real-time. Therefore, IKE and tropical cyclone structure are analyzed within historical Atlantic tropical cyclones from the past two decades in order to develop an...
Show moreIntegrated kinetic energy (IKE) is a recently developed metric that approximates the destructive potential of a tropical cyclone by assessing the size and strength of its wind field. Despite the potential usefulness of the IKE metric, there are few, if any, operational tools that are specifically designed to forecast IKE in real-time. Therefore, IKE and tropical cyclone structure are analyzed within historical Atlantic tropical cyclones from the past two decades in order to develop an understanding of the environmental and internal storm-driven processes that govern IKE variability. This analysis concurs with past research that IKE growth and decay is influenced by both traditional tropical cyclone development mechanisms and by other features such as extratropical transition and trough interactions. Using this framework, a series of statistical prediction tools are created in an effort to project IKE in Atlantic tropical cyclones from a series of relevant normalized input parameters. The resulting IKE prediction schemes are titled the "Statistical Prediction of Integrated Kinetic Energy (SPIKE)". The first version of SPIKE utilizes simple linear regression to project historical IKE quantities in a perfect prognostic mode for all storms between 1990 and 2011. This primitive model acts as a proof of concept, revealing that IKE can be skillfully forecasted relative to persistence out to 72 hours by even the simplest of statistical models if given accurate estimates of various metrics measured throughout the storm and its environment. The proof-of-concept version of SPIKE is improved upon in its second version, SPIKE2, by incorporating a more sophisticated system of adaptive statistical models. A system of artificial neural networks replaces the linear regression model to better capture the nonlinear relationships in the TC-environment system. In a perfect prognostic approach with analyzed input parameters, the neural networks outperform the linear models in nearly every measurable way. The system of neural networks is also more versatile, as it is capable of producing both deterministic and probabilistic tools. Overall, the results from these perfect prognostic exercises suggest that SPIKE2 has a high potential skill level relative to persistence and several other benchmarks. Finally, in an effort to assess its real-time performance, the SPIKE2 forecasting system is run in a mock-operational hindcast mode for the 1990 to 2011 North Atlantic hurricane seasons. Hindcasts of IKE are produced in this manner by running the neural networks with hindcasted input parameters from NOAA's second generation Global Ensemble Forecast System reforecast dataset. Ultimately, the results of the hindcast exercises indicate that the neural network system is capable of skillfully forecasting IKE in an operational setting at a level significantly higher than climatology and persistence. Ultimately, forecasts of IKE from these neural networks could potentially be an asset for operational meteorologists that would complement existing forecast tools in an effort to better assess the damage potential of landfalling tropical cyclones, particularly with regards to storm surge damage.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9376
Format: Thesis

Title: ENSO Variability in a Changing Climate.
Creator: Feng, Jiaxin, Wu, Zhaohua, Ye, Ming, Clarke, Allan J., Liu, Guosheng, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreFeng, Jiaxin, Wu, Zhaohua, Ye, Ming, Clarke, Allan J., Liu, Guosheng, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: Since 1980, a new type of ENSO, i.e., central Pacific (CP) ENSO, where sea surface temperature anomalies (SSTAs) are mainly located in the equatorial central Pacific, has been frequently observed. Several studies have documented and predicted a higher occurrence ratio of CP ENSO to eastern Pacific (EP) ENSO, where SSTAs mainly occur in the equatorial eastern Pacific, in a warming climate. Most studies centered on the difference between CP and EP ENSO have used traditional analysis methods,...
Show moreSince 1980, a new type of ENSO, i.e., central Pacific (CP) ENSO, where sea surface temperature anomalies (SSTAs) are mainly located in the equatorial central Pacific, has been frequently observed. Several studies have documented and predicted a higher occurrence ratio of CP ENSO to eastern Pacific (EP) ENSO, where SSTAs mainly occur in the equatorial eastern Pacific, in a warming climate. Most studies centered on the difference between CP and EP ENSO have used traditional analysis methods, such as PCA/EOF analysis and regression, to define or differentiate the aforementioned two types of ENSO. However, the results obtained using these methods can only reveal accumulated spatial information which contributed most to the variance of the data, which is the usually the spatial information during the mature (peak) stage of ENSO; this spatial information is a static pattern and is not able to reveal sequential development of ENSO, which should be crucial for physical interpretations. In addition, although this spatial information in generally true for the entire temporal span, it is not necessarily true for any subperiods and thus not able to reveal any potential characteristic change of ENSO over time. In this study, an alternative Niño 3.4 index is defined to reflect only the interannual variability of equatorial Pacific SSTAs. Using this alternative index, we identify 28 El Niño events and 31 La Niña events. Then, we employ a newly developed analysis method, i.e., fast multidimensional ensemble empirical mode decomposition (FMEEMD), to extract the interannual spatiotemporal evolution of SSTAs to examine the developments of the identified ENSO events. All events are classified into four types of ENSO based on the interannual evolutions of SSTAs early in the development stage: (1) EP ENSO, (2) eastern-central Pacific (ECP) ENSO, (3) western-central Pacific (WCP) ENSO, and (4) mixed (MIX) ENSO. We apply the same method to analyze surface horizontal wind and thermocline depth data, and phase composite analyses on SSTAs, surface wind anomalies and thermocline depth anomalies are performed for each type of El Niño events. The results show four distinctive evolution patterns; it is found that La Niña events also have similar variation in the evolution patterns. The lower-frequency variability and change (decadal and longer time scales, including secular trend trend) in SSTAs, surface wind anomalies and thermocline depth anomalies are also examined. The secular trends show weak surface cooling over the central Pacific between 140°W and 160°W near the Equator, consistent with the anomalous wind divergence and thermocline shoaling in the same region. In response to decadal and lower-frequency oscillatory wind forcing, the background state of the thermocline is modified in a way that when western-central Pacific is dominated by shoaling (deepening), the eastern Pacific is dominated by deepening (shoaling). The combined effect of the secular trends and lower-frequency oscillatory variability is that for some decade(s), the thermocline depth is anomalously shallower (deeper) in the western-central Pacific region, while the thermocline depth is anomalously deeper (shallower) in the east. We suggest that this "seesaw" pattern in the depth anomalies across the Equator determines the evolving patterns of ENSO by hinder/facilitating the communication between ocean surface and subsurface, and thus modifying the effect of wave-associated thermocline displacements on SST change over the western-central Pacific. Additionally, for WCP and some of the MIX ENSO events, a potential SSTA precursor from Baja California/northeastern Pacific might be instrumental to the subsequent development, possibly by inducing zonal wind anomalies in the western Pacific.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9330
Format: Thesis

Title: Biases in Satellite-Derived Temperature Trends Due to Orbital Drift, Orbital Differences and Their Corrections.
Creator: Chen, Hong, Cai, Ming, Ray, Peter S., Wu, Zhaohua, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: The measurements from Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit-A (AMSU-A) have been extensively used for atmospheric temperature trend study during last several decades. The existences of inter-sensor biases and orbital drift, orbital differences among different satellites are two major challenges for climate study using long-term time series of satellite measurements. In this study, the impacts of orbital drift and orbital differences of satellites on AMSU-A derived...
Show moreThe measurements from Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit-A (AMSU-A) have been extensively used for atmospheric temperature trend study during last several decades. The existences of inter-sensor biases and orbital drift, orbital differences among different satellites are two major challenges for climate study using long-term time series of satellite measurements. In this study, the impacts of orbital drift and orbital differences of satellites on AMSU-A derived temperature trends over Amazon rainforest are investigated. The AMSU-A near-nadir observations from NOAA-15, NOAA-18, NOAA-19, and MetOp-A during 1998 - 2014 are employed. The double difference method is firstly applied to obtain the estimates of inter-sensor biases for each paired AMSU-A instruments, in which NOAA-18 is used as a reference satellite. The inter-calibrated observations from the four satellites mentioned above are used to calculate monthly mean diurnal cycles of brightness temperature for each of the 15 AMSU-A channels. The diurnal correction method is then applied to all AMSU-A data using the estimated diurnal-cycle variations in order to obtain corrected data valid at the same local time. Finally, it is shown that the inter-sensor bias correction and diurnal correction have significant impacts on the AMSU-A derived long-term atmospheric temperature trends.
Show less
Date Issued: 2015
Identifier: FSU_migr_etd-9303
Format: Thesis

Title: An Examination of the Differences in Tropical Cyclone Pressure-Wind Relationships Among Observations, Model Analyses, and Model Forecasts.
Creator: Visin, Lauren, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: Despite significant advances in tropical cyclone (TC) track forecasting over the past few decades, intensity forecasts remain problematic, even for high-resolution computer models uniquely developed and tailored to TC prediction. This study examines the ability of two of these models, the Geophysical Fluid Dynamics Laboratory (GFDL) model and the Hurricane Weather Research and Forecasting (HWRF) model, to analyze and predict one measure of TC structure in the Atlantic Basin. Instead of more...
Show moreDespite significant advances in tropical cyclone (TC) track forecasting over the past few decades, intensity forecasts remain problematic, even for high-resolution computer models uniquely developed and tailored to TC prediction. This study examines the ability of two of these models, the Geophysical Fluid Dynamics Laboratory (GFDL) model and the Hurricane Weather Research and Forecasting (HWRF) model, to analyze and predict one measure of TC structure in the Atlantic Basin. Instead of more conventional evaluations based solely on a TC's maximum wind speed or minimum sea level pressure (MSLP), the relationship between these two variables is used: a TC's pressure-wind relationship (PWR), which gives a more detailed look at how well each model analyzes and forecasts TC structure. The analysis begins in 2007, the year the GFDL was initially "frozen" (development and improvements were ceased) and also the first year that the HWRF was used for operational forecasting. Comparison of both GFDL and HWRF analyses and forecasts to the National Hurricane Center's (NHC) "best track" (database of 6-hourly observations of vital statistics such as maximum wind speed and MSLP for all TCs) revealed that, while both models produced errors in their analyses and forecasts, the GFDL outperformed the HWRF in both analysis and forecasting of TC PWR's for Atlantic Basin hurricanes from 2007-2013.. There was a subsection of particularly strong TCs (maximum winds above 120kt, MSLP lower than 950mb) whose structure was forecast especially poorly. The forecast PWR's produced by the HWRF fell largely outside the "best track" for this set of intense TCs, suggesting that the structures produced by the HWRF are inconsistent with our best estimates of observations in the Atlantic Basin and given current climate conditions. The PWR distribution evolved considerably for the HWRF over time, presumably as model improvements were made (including a decrease in model gridspacing). This has led to the model analysis PWR becoming more consistent with the model forecast PWR envelope. Nonetheless, both often fall outside the best-track estimates of PWR and potential explanations for this disparity are presented.
Show less
Date Issued: 2014
Identifier: FSU_migr_uhm-0386
Format: Thesis

Title: The Accuracy of the National Hurricane Center's United States Tropical Cyclone Landfall Forecasts in the Atlantic Basin (2004–2012).
Creator: Keclik, Alexandra, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: This study examined the position, timing, and intensity of each National Hurricane Center's (NHC) Official Forecasts (OFCL) for Atlantic tropical storms and hurricanes that made landfall in the United States from 2004 to 2012. During that time period, one hundred and fifty tropical cyclones developed in the Atlantic basin. Thirty-two of the cyclones made landfall in the United States as tropical storms or hurricanes. Accurate predictions of the location, timing, and intensity of tropical...
Show moreThis study examined the position, timing, and intensity of each National Hurricane Center's (NHC) Official Forecasts (OFCL) for Atlantic tropical storms and hurricanes that made landfall in the United States from 2004 to 2012. During that time period, one hundred and fifty tropical cyclones developed in the Atlantic basin. Thirty-two of the cyclones made landfall in the United States as tropical storms or hurricanes. Accurate predictions of the location, timing, and intensity of tropical cyclone landfalls are important, so that people in a storm's track can prepare adequately for heavy to catastrophic wind, rain, and storm surge. The errors of each of the OFCL for Atlantic tropical storms and hurricanes that made landfall in the United States during 2004–2012 are acquired from the Best Track data set. The ELTOPO1 landmask is used to find the forecasted landfall point using sequential locations from the OFCL offshore and onshore points of each forecast. The great circle distance between the forecasted and actual landfall constitutes the location error. The official landfall time is subtracted from the forecasted landfall time to find the timing error, and the official landfall wind speed is subtracted from the closest to onshore wind speed to find intensity error. There is a trend of decreasing error in location, timing, and intensity forecasting with decreasing lead time. An improvement in tropical cyclone landfall forecasting is found from comparing the 2004–2012 Atlantic landfall forecast errors to those in a study of 1976-2000 forecasts.
Show less
Date Issued: 2014
Identifier: FSU_migr_uhm-0324
Format: Thesis

Title: The Increasing Intensity and Frequency of ENSO and its Impacts to the Southeast U.S.
Creator: McNaught, Carlysle, Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: The El Niño Southern Oscillation (ENSO) is an important natural climate variation that affects large portions of the world. The changing magnitude and frequency of ENSO reveals that it is getting stronger as measured by the maximum anomaly in sea surface temperature (SST). Principal component analysis of the ENSO is conducted to estimate the spectrum of the SST of the time series. The intensity of the ENSO events during the period 1970—2010 is statistically significantly higher when compared...
Show moreThe El Niño Southern Oscillation (ENSO) is an important natural climate variation that affects large portions of the world. The changing magnitude and frequency of ENSO reveals that it is getting stronger as measured by the maximum anomaly in sea surface temperature (SST). Principal component analysis of the ENSO is conducted to estimate the spectrum of the SST of the time series. The intensity of the ENSO events during the period 1970—2010 is statistically significantly higher when compared to the period 1930—1970, with a broad spectral peak centered around 4 years. When we compare the SST spectrum for the period 1930—1970 with the spectrum for 1970—2010, we find the latter period to be much stronger in power. The resultant impact of more powerful and frequent ENSO events on the Southeast United States is examined through a spatial and temporal statistical analysis of precipitation and temperatures between the two time periods. Our analysis reveals statistically significant changes in precipitation during El Niño where the rainfall is much more widespread across the Southeast during the 1970—2010 period than the 1930—1970 period. The La Niña rainfall deficit is mainly confined to Florida in the latter period than the former. Finally, the temperature distribution, through an analysis of the first four statistical moments, showed conventional responses to the changes in ENSO precipitation such as an anomalous decrease in maximum temperatures during El Niño and an overall anomalous increase in temperatures during La Niña.
Show less
Date Issued: 2014
Identifier: FSU_migr_uhm-0356
Format: Thesis

Title: Hurricane Sandy and New Jersey: The Nature of a Natural Disaster.
Creator: Blaskiewicz, Claire S., Department of Earth, Ocean and Atmospheric Sciences
Abstract/Description: While natural disasters can often be catalysts for change, understanding where to begin changing can be discovered by looking at the science and history of the affected area. Hurricane Sandy's unprecedented landfall in October 2012 began this progression for the state of New Jersey. This study examines the processes affecting the ocean and beaches of New Jersey, looks at the effects of Hurricane Sandy on the state and discusses the changing standards that have been and continue to be enacted...
Show moreWhile natural disasters can often be catalysts for change, understanding where to begin changing can be discovered by looking at the science and history of the affected area. Hurricane Sandy's unprecedented landfall in October 2012 began this progression for the state of New Jersey. This study examines the processes affecting the ocean and beaches of New Jersey, looks at the effects of Hurricane Sandy on the state and discusses the changing standards that have been and continue to be enacted since storm recovery began. Specifically highlighted are the engineering practices of flood mitigation, the effects of the storm on the state's economy and the new policies and standards that have come about in the aftermath.
Show less
Date Issued: 2014
Identifier: FSU_migr_uhm-0564
Format: Thesis

Title: Deep-Sea Faunal Investigations from Macrofaunal Abundance to Harpacticoid (Crustacea Analyses of Harpacticoids.
Creator: Easton, Erin E., Thistle, David, Steppan, Scott, Huettel, Markus, Kostka, Joel, MacDonald, Ian, Terebelski, Patricia Spears, Department of Earth, Ocean and Atmospheric Sciences,...
Show moreEaston, Erin E., Thistle, David, Steppan, Scott, Huettel, Markus, Kostka, Joel, MacDonald, Ian, Terebelski, Patricia Spears, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Show less
Abstract/Description: The deep-sea, soft-bottom habitat is considered the largest ecosystem on Earth, yet little is known about the biogeography of the infauna. This dissertation examines the species' ranges of the meiofaunal taxon Harpacticoida (Crustacea: Copepoda) and the macrofaunal abundance and similarity for the continental rise off the west coast of the United States. Specifically, I examined these fauna at two depths (2700 and 3700 m) and at four latitudes (approximately 34 N, 37 N, 40 N, and 43 N). To...
Show moreThe deep-sea, soft-bottom habitat is considered the largest ecosystem on Earth, yet little is known about the biogeography of the infauna. This dissertation examines the species' ranges of the meiofaunal taxon Harpacticoida (Crustacea: Copepoda) and the macrofaunal abundance and similarity for the continental rise off the west coast of the United States. Specifically, I examined these fauna at two depths (2700 and 3700 m) and at four latitudes (approximately 34 N, 37 N, 40 N, and 43 N). To examine the species ranges of deep-sea harpacticoids, I used morphological and DNA-sequencing methods to assign individuals to species. To do so, I had to first develop new primers for my target genes. In the process of designing primers, I sequenced the complete mitochondrial genome, which is the eighth to be sequenced, of one species of shallow-water harpacticoid and ~75% of another (Chapter 2). The two mitochondrial genomes were nearly identical to each other and were more similar to the mitochondrial genome of a Poecilostomatitoida (Crustacea: Copepoda) than to the other Harpacticoida mitochondrial genomes. Copepod mitochondrial genomes are highly rearranged, so this similarity among copepod orders supports studies that suggest mitochondrial gene arrangements could be used to reconstruct copepod phylogenies. In addition to developing new primers, I had to develop an efficient DNA isolation method (Chapter 3) for individual copepods that would allow me to recover intact exoskeletons for morphological analysis. With this method, I was able to recover intact exoskeletons suitable for morphological analysis 91.6% of the time. The DNA isolated was stable for up to 32 months, and the nuclear 18S rRNA and mitochondrial cytb primers designed and tested amplified 96.6% and 96.3% of the individuals respectively. Of the 160 deep-sea individuals with morphological, 18S, and cytb data that were used in the species' range study (Chapter 4), they were assigned to 54 species on the basis of congruency among the data. Of the 45 species that had more than one individual, 13 had 1000-km-scale ranges and another 10 had 500-km-scale ranges. These results were surprising because previous studies had suggested that morphologically identical but genetically distinct (cryptic) species were common for harpacticoids, so I expected the large (> 1000 km) ranges reported for morphological studies were over estimates. This study is the first to use morphological and molecular methods to assign deep-sea harpacticoids to species, and I found only one case of cryptic species and 18 cases of phenotypically diverse species. In Chapter 5, I report macrofaunal abundance and similarity of the southern six stations and identify environmental variables the best explain variation among my stations. I found that depth patterns in abundance were group-specific and that all groups either did not differ significantly with depth or decreased significantly with depth. The environmental variables that had parallel patterns with those groups that did decrease significantly with depth were chlorophyll a and the stable isotope 15N, which are proxies for food. Regional patterns were also group specific but no environmental variables showed parallel patters with regional differences. Aplacophoran mollusks were the largest contributor to depth and regional faunal dissimilarity, and depth, 15N, and sediment particle-size distribution best explained the variation in the multivariate cloud of faunal similarity.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8977
Format: Thesis

Title: The Transport of Ship Emissions in the Strait of Malacca Using a High-Resolution WRF Simulation and Low-Resolution GDAS Data Coupled with Hysplit.
Creator: Hall, Tristan James, Fuelberg, Henry E., Hart, Robert, Misra, Vasu, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The goal of this research is to describe and quantify the role of deep convection within the Strait of Malacca (hereafter referred to as the "Strait" a part of the Maritime Continent in Southeast Asia) on the long-range transport of ship emissions. It utilizes a combination of the Weather Research and Forecasting (WRF) Model with a 2 km horizontal grid spacing and the HYbrid Single Particle Lagrangian Integrated Trajectories model (HYSPLIT 4). Results from the high-resolution WRF simulations...
Show moreThe goal of this research is to describe and quantify the role of deep convection within the Strait of Malacca (hereafter referred to as the "Strait" a part of the Maritime Continent in Southeast Asia) on the long-range transport of ship emissions. It utilizes a combination of the Weather Research and Forecasting (WRF) Model with a 2 km horizontal grid spacing and the HYbrid Single Particle Lagrangian Integrated Trajectories model (HYSPLIT 4). Results from the high-resolution WRF simulations are compared to the coarse-resolution (1° horizontal grid spacing) Global Data Assimilation System (GDAS) data provided by the Air Resources Laboratory. World Wide Lightning Network (WWLLN) observations reveal that the Strait region has a pronounced diurnal cycle of lightning with a nighttime (1900–0700 LT) maximum that is 2–3 times greater in the Strait itself than the daytime (0700–1900 LT) maximum on the surrounding landmasses. WWLLN observations also reveal that the Strait region has a seasonal cycle that is influenced by the Intertropical Convergence Zone and is out of phase with the Asian monsoon. April is the month with the most lightning, followed by October. Conversely, February is the month with the least amount of lightning. Therefore, these three months are the focus of this study. The Emissions Database for Global Atmospheric Research v4.2 is used to find an average emissions rate from ships within the Strait. A mass is assigned to each HYSPLIT particle in order to display a three-dimensional representation of CO concentrations. HYSPLIT results using WRF as the meteorological input reveal that more CO is transported to the upper troposphere/lower stratosphere (UTLS) during April than any other month. October is also efficient at transporting CO to the UTLS, but in smaller concentrations than April. CO transport during February is primarily in the lower to middle troposphere. The effect of model resolution is shown by comparing WRF-derived trajectories to GDAS-derived trajectories. The coarse-resolution GDAS-derived trajectories remain close to their point of release after 120 h. The high-resolution WRF-derived trajectories exhibit more horizontal and vertical transport than GDAS. Result of vertical mass flux calculations show that April has the greatest influence on the UTLS which is consistent with WWLLN lightning observations and a climatology of GDAS convective available potential energy within the Strait. April has the greatest hydrostatic instability of the three months studied, and therefore has the most lightning and deepest transport; October is second in this regard; and February is third.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9000
Format: Thesis

Title: Spatiotemporal Inhomogeneity of Mixed Rossby-Gravity Waves.
Creator: Sun, Jie, Wu, Zhaohua, Bourassa, Mark A., Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: Tropical atmospheric waves play a major role in the variability and change of weather and climate in the tropics as well as in the globe. They also interact with other tropical systems such as tropical cyclones (TCs) and El Niño-Southern Oscillation (ENSO). The improved understanding of the tropical waves, such as their origins, their spatiotemporal structures, and their life cycles, can lead to better prediction of weather and climate change in the tropics as well as over many other areas of...
Show moreTropical atmospheric waves play a major role in the variability and change of weather and climate in the tropics as well as in the globe. They also interact with other tropical systems such as tropical cyclones (TCs) and El Niño-Southern Oscillation (ENSO). The improved understanding of the tropical waves, such as their origins, their spatiotemporal structures, and their life cycles, can lead to better prediction of weather and climate change in the tropics as well as over many other areas of the globe. Most of the previous diagnoses of observed tropical waves came from two categories: (1) case studies in which individual waves of particular types are examined, leading to scattered information of the spatiotemporal characteristics of these waves; and (2) climatological studies using wavenumber-frequency domain analysis which is not able to identify spatiotemporal inhomogeneity of tropical waves. To fill the gap between these two approaches, we use a recently developed spatiotemporally local analysis method, the multi-dimensional ensemble empirical mode decomposition (MEEMD) method, and known spatial wind structures of different types of waves to systematically extract the evolution information of tropical waves over large temporal and spatial domains. Through further analysis of the extracted wave events, the spatiotemporal inhomogeneity of tropical waves is characterized. In this study, as the very first step toward a comprehensive study, our focus is placed on mixed Rossby-gravity (MRG) waves. The propagation characteristics, period, and horizontal (zonal and meridional) scale of MRG events detected in this study can match with both the theoretical results and observational studies. There are 23 MRG events detected from the 3rd MEEMD component in the year 2002, among which most events occurred over the western Pacific Ocean and fewest MRG events over the Indian Ocean. The phase velocity and meridional scale are largest over the Atlantic Ocean while smallest in the Indian Ocean. The locations and propagation characteristics of MRG events show great spatiotemporal inhomogeneity. After the evolution of MRG events are obtained, they can be connected with TCs. A new hypothesis, which better matches the observation, is proposed that the swelling and westward propagation of MRG wave pattern help the TCs moving westward and toward higher latitudes, which is necessary for TCs to develop at early stage.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9255
Format: Thesis

Title: The Influence of Small-Scale Sea Surface Temperature Gradients on Surface Vector Winds and Subsequent Impacts on Oceanic Ekman Pumping.
Creator: Hughes, Paul J., Bourassa, Mark A., Chassignet, Eric, Dewar, William, Liu, Guosheng, Zou, Xiaolei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Satellite observations have revealed a small-scale (
Show moreSatellite observations have revealed a small-scale (< 1000 km) air-sea coupling in regions of strong sea surface temperature (SST) gradients (e.g., fronts, currents, eddies, and tropical instability waves), where the surface wind and wind stress are modified. Surface winds and wind stresses are persistently higher over the warm side of the SST front compared to the cool side, causing perturbations in the dynamically and thermodynamically curl and divergence fields. Capturing this small-scale SST-wind variability is important because it can significantly impact both local and remote (i.e., large scale) oceanic and atmospheric processes. The SST-wind relationship is not well represented in numerical weather prediction (NWP) and climate models, and the relative importance of the physical processes that are proposed to be responsible for this relationship is actively and vehemently debated. This study focuses on the physical mechanisms that are primarily responsible for the SST-induced changes in surface wind and wind stress, and on the physical implication on ocean forcing through Ekman pumping. The roles that SST-induced atmospheric baroclinicity and boundary-layer stability play in modifying the surface vector wind in regions of strong SST gradients are examined with an idealized model. Modeled changes in surface wind speed due to changes in atmospheric boundary-layer stability and baroclinicity are largely between -2.0 and 2.0 m s-1, which is consistent with past observational findings. The baroclinic-related changes in the surface vector wind are found to have a largely linear dependence on the SST gradient, whereas the stability-related changes are highly non-linear. The linearity of the baroclinic impacts matches that of the observed (satellite and in situ) SST-wind relationship. This result suggests that the baroclinic-related mechanism is the leading factor in driving the observed surface wind response to strong open ocean SST fronts on scales greater than 25 km. This study shows that the baroclinic-related changes in Ekman pumping are significant (first-order) over a seasonal (2003 winter season) time scale and that the small-scale impacts are quite important over larger spatial scales. These findings highlight the need to consider the small-scale SST-wind relationship even in coarser resolution model simulation, for which it may be feasible to parameterize because of the linear nature of the baroclinic-related effects.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9008
Format: Thesis

Title: On Initializing CGCMs for Seasonal Predictability of ENSO.
Creator: Michael, J-P, Misra, Vasu, Burmester, Mike, Chassignet, Eric P., Wu, Zhaohua, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Initializing Coupled General Circulation Models (CGCMs) for routine seasonal ENSO prediction is currently an onerous task. This is one of the main reasons on why the CGCMs participating in the Coupled Model Intercomparison Project 5 (CMIP5), which represents the state-of-the-art in climate modeling, is infrequently used for routine seasonal prediction of El Niño and the Southern Oscillation (ENSO), the largest known natural variability that affects the global climate. In this work we propose...
Show moreInitializing Coupled General Circulation Models (CGCMs) for routine seasonal ENSO prediction is currently an onerous task. This is one of the main reasons on why the CGCMs participating in the Coupled Model Intercomparison Project 5 (CMIP5), which represents the state-of-the-art in climate modeling, is infrequently used for routine seasonal prediction of El Niño and the Southern Oscillation (ENSO), the largest known natural variability that affects the global climate. In this work we propose a simple ocean initialization technique that can be adopted for any CGCM for seasonal predictability studies of ENSO. The technique entails finding the best analogues from a long historical simulation of the CGCM to the targeted air-ocean initial state. Since this study is on seasonal ENSO predictability, the metrics chosen to pick the analogues were confined to a set of 4 variables in the tropical Pacific that were found sensitive to the Niño3.4 SST variations. They were Tropical Pacific SSTs, thermocline depth, time tendency of thermocline depth, and the zonal wind stress. The multiobjective optimization technique was used to optimize the overall analogue match across the four variables giving equal weighting to each. This in effect uses the minimum root mean square difference between the targeted initial state and the model states to pick the analogue from the historical simulation of the CGCM that matched the targeted initial state. The chosen analogues were then perturbed using empirical singular vectors to provide additional initial conditions to generate in total 12 ensemble members per seasonal hindcast. The methodology for ocean initialization was first tested with the Cane-Zebiak model, a two layer reduced gravity ocean model coupled to a statistical atmosphere. We found that the methodology is sensitive to the length of the library generated from the historical simulation of the model and also on the fidelity of the model in simulating the ENSO. These toy model experiments also revealed the benefit of using a multi-variate metric to choose the analogues. Before proceeding to conduct the proposed work with a CGCM, the CMIP5 historical simulations for the 20th century were analyzed for their ENSO simulation. The mean-state and ENSO variations were analyzed in both the atmosphere and ocean. It was found that most of the CMIP5 models exhibit cold (warm) biases in the equatorial (subtropical eastern) Pacific Ocean sea surface temperature that are reminiscent of the split inter-tropical convergence zone phenomenon. There is, however, a major improvement in the representation of the power spectrum of the Niño3.4 sea surface temperature variations which shows that, as in the observations, a majority of the models display a spectral peak in the 2-7 year range, have a near linear relationship with the displacement of the equatorial thermocline and exhibit a robust atmospheric response to ENSO variations. Several issues remain in the CMIP5 simulations such as erroneous amplitudes in the Niño3.4 sea surface temperature spectrum's peak and a width of the spectral peak that is either too broad or too narrow. It is also seen that most CMIP5 models unlike the observations extend the ENSO variations in the equatorial Pacific too far westward beyond the dateline and there is very little asymmetry in event duration between the warm and cold phases. ENSO variability forces a dominant mode of rainfall variability in the southeastern United States, especially in the boreal winter season. The CMIP5 exhibited a wide range of response in this metric with several displaying weak to non-existent, some showing relatively strong, and one indicating excessively zonally-symmetric teleconnection over the southeastern United States. Based on this study we choose to use the CCSM4, which displayed a reasonable ENSO simulation for our experimental seasonal hindcasts with the proposed ocean initialization strategy. The seasonal hindcasts were initiated in beginning of March of each year from 1980-2012 follows from seeking a model state that minimizes the RMS difference in SST, zonal wind stress, thermocline depth and thermocline depth tendency from a 600 year continuous integration of the CCSM4 with the corresponding metric in the Global Ocean Data Assimilation (GODAS) of the National Centers for Environmental Prediction (NCEP). The four variables are jointly optimized by multi-objective optimization of the resulting root mean squared (RMS) difference curves, essentially minimizing the normalized RMS in all four parameters. Some of the main highlights of our results from the seasonal hindcasts are: i) The deterministic skill as measured by the anomaly correlation of the monthlyensemble mean and observed SST anomalies in the Niño3.4 region at 9-month lead is 0.71. ii) The probabilistic prediction of the Niño3.4 SST anomalies at 9-month lead for warm and cold ENSO events as measured by the area under the Relative Operating Characteristic Curve is 0.7 and 0.8 respectively. Likewise the brier skill score for warm and cold ENSO events at 9-month lead for Niño3.4 SST anomalies is 0.11 and 0.21 respectively. iii) The global teleconnection patterns in SST, precipitation and 500hPa geopotential heights with Niño3.4 SST variations in the seasonal hindcast in Oct-November-December season (7 month lead) is reasonable. From these results we demonstrate that the proposed initialization strategy is viable to deploy many other existing CMIP5 models for either operational seasonal ENSO prediction or ENSO predictability studies.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9050
Format: Thesis

Title: Polarization Signature in Micro-Wave Humidity Sounder Window Channels.
Creator: Chen, Xu, Zou, Xiaolei, Ellingson, Robert G., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Microwave Humidity Sounders (MHS) onboard NOAA-15, -16, -17, -18, -19 and EUMETSAT MetOp-A, -B provide radiance measurements at a single polarization state at any of the five observed frequencies. Microwave Humidity Sounder (MWHS) onboard FengYun-3 (FY-3) satellite has a unique instrument design and provides dual polarization measurements at 150 GHz. In this study, the MWHS polarization signal is investigated using observed and modeled data. It is shown that the quasi-polarization brightness...
Show moreMicrowave Humidity Sounders (MHS) onboard NOAA-15, -16, -17, -18, -19 and EUMETSAT MetOp-A, -B provide radiance measurements at a single polarization state at any of the five observed frequencies. Microwave Humidity Sounder (MWHS) onboard FengYun-3 (FY-3) satellite has a unique instrument design and provides dual polarization measurements at 150 GHz. In this study, the MWHS polarization signal is investigated using observed and modeled data. It is shown that the quasi-polarization brightness temperatures at 150 GHz display a scan angle dependent bias. Under calm ocean conditions, the polarization difference at 150 GHz becomes non-negligible when the scan angle varies from 10 to 45 degrees and reaches a maximum when the scan angle is about 30 degrees. Also, the polarization state is sensitive to surface parameters such as surface wind speed. Under clear-sky conditions, the differences between horizontal and vertical polarization states at 150 GHz increase with decreasing surface wind speed. Therefore, the polarization signals from the cross-track scanning microwave measurements at window channels contain useful information of surface parameters. What is more, cloud liquid water is also proved to be a non-ignorable factor reducing the difference between horizontal and vertical polarization states at 150 GHz. Also, the availability of dual polarization measurements allows a one-to-one conversion from the antenna brightness temperature to sensor brightness temperature if there exit a cross-polarization spill-over.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8755
Format: Thesis

Title: Exploring a Comparative Climatology of Tropical Cyclone Core Structures.
Creator: Cossuth, Joshua Howard, Hart, Robert, Elsner, James, Bourassa, Mark, Dewar, William, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The structure of a tropical cyclone (TC) is a spatial representation of its organizational pattern and distribution of energy acquisition and release. This fingerprint depicts a specific phase in the TC's meteorological lifecycle, reflecting its past and potentially constraining its future development. For a number of reasons, a thorough objective definition of TC structures (especially at the TC core) and an intercomparison of their varieties have been neglected. This lack of knowledge...
Show moreThe structure of a tropical cyclone (TC) is a spatial representation of its organizational pattern and distribution of energy acquisition and release. This fingerprint depicts a specific phase in the TC's meteorological lifecycle, reflecting its past and potentially constraining its future development. For a number of reasons, a thorough objective definition of TC structures (especially at the TC core) and an intercomparison of their varieties have been neglected. This lack of knowledge impedes a fuller understanding of TCs, possibly signaling a key reason why TC intensity forecasts, despite numerical model improvements and theoretical advances, have been stagnant in recent years relative to track forecasts. To improve the understanding and forecasting of tropical cyclones, this research aggregates known methods to identify structure and proposes expanded metrics of structural diagnosis. A 24 year record of limited operational core structure attributes - including aircraft reconnaissance measurements and estimates by operational forecasters - are examined and shown to tease the potential capability of TC structure to guide analysis and forecasting. To mitigate these data set limitations, a new global 26 year multi-platform dataset of satellite microwave imagery is gathered and standardized to facilitate an expanded climatological survey of tropical cyclone structures. New types of structure metrics are objectively developed using morphometric analysis techniques (i.e. size and shape analysis of TC features) based on known tropical cyclone critical features, thereby facilitating a comparison with operational data. A climatology of TC core structures is presented, demonstrating the observed existence of intensity, size, and shape information in aircraft and satellite data. Composites of relationships between intensity and size metrics show preferred configurations that depend on a TC's structural state. While the newly defined structures provide additional dimensionality that is related to intensity, some TC size relationships are shown to be invariant with intensity. This comparative analysis of observed structural metrics provides further insight in understanding the relationship between TC structural features, to what extent they indicate intensity change, and what physical processes lead to their formation and decay.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8965
Format: Thesis

Title: Forecasting Lightning Cessation Using Data from a Network of Field Mills at Kennedy Space Center and Cape Canaveral Air Force Station.
Creator: Seay, Brannon Adrian, Fuelberg, Henry E., Hart, Robert, Ahlquist, Jon, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Improving lightning cessation forecasts is important to operations of the 45th Weather Squadron (45WS) at Kennedy Space Center (KSC). If lightning advisories can be cancelled closer to the time that cessation actually occurs without compromising safety, there is the opportunity to save time, money, and improve the scheduling of space launches. This paper describes the use of data from a network of 31 field mill (FM) sensors located at KSC and Cape Canaveral Air Force Station (CCAFS) to...
Show moreImproving lightning cessation forecasts is important to operations of the 45th Weather Squadron (45WS) at Kennedy Space Center (KSC). If lightning advisories can be cancelled closer to the time that cessation actually occurs without compromising safety, there is the opportunity to save time, money, and improve the scheduling of space launches. This paper describes the use of data from a network of 31 field mill (FM) sensors located at KSC and Cape Canaveral Air Force Station (CCAFS) to determine whether a storm's last flash has occurred based on surface electric field values under thunderstorms. Along with the FM data, radar derived products are utilized in developing and analyzing the forecasting schemes. The dataset consists of warm season, quasi-isolated thunderstorms in east central Florida from 2009 - 2012. Radar products are used from the Tampa (KTBW) and Melbourne (KMLB) National Weather Service radars. Lightning data from the Lightning Detection and Ranging - Second Generation (LDAR-II) network also are utilized. LDAR-II detects source emissions from both intra-cloud (IC) and cloud-to-ground (CG) flashes. Rapid Update Cycle (RUC) and Rapid Refresh (RAP) model analyses are used to describe environmental conditions of the storms. The storms are tracked using the Warning Decision Support System - Integrated Information software (WDSS-II). Based on multiple FM derived variables and maximum reflectivity at -10°C altitude, algorithms are developed using various thresholds and wait times. Then, combinations of FM and radar parameters are used to create new algorithms. Skill scores are calculated for each algorithm based on the number of hits (correct forecasts), false alarms (cancelling an advisory prior to cessation), and misses (never ending an advisory). Since false alarms present the most dangerous situations, they are the most heavily weighted in selecting the best performing algorithms. The times after successful cancellations are determined and compared to current 45WS' approaches. Results indicate that while algorithms using only FM data show forecast skill and save time, they are not sufficiently safe. Conversely reflectivity algorithms produce zero false alarms, but yield too many misses. Algorithms combining the FM and radar data give the best results. The overall best performing algorithm includes the one minute standard deviations of the data from the FM sensor closest to the last flash initiation point (S1CL) at a threshold of 380 V m-1 s-1, a reflectivity threshold of 35 dBZ, and a 5 min wait time. This combination does not prematurely suspend an advisory for any of the storms analyzed. On average, it ends advisories 9.91 min after cessation occurs, an improvement of 20.09 min based on the 45WS' most conservative approach of 30 min. These results show that the FM network at KSC/CCAFS in combination with radar products can be useful in improving lightning cessation forecast guidance.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8884
Format: Thesis

Title: Estimating the Effects of Climate Change on Tropical Cyclone Activity.
Creator: Seitz, Chana, Misra, Vasu, LaRow, Timothy, Hart, Robert, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The effects of two different future warming climate scenarios on Global and North Atlantic named tropical cyclone (NTC) activity is examined using the Florida State University/Center for Ocean-Atmospheric Prediction Studies (FSU/COAPS) atmospheric general circulation model (AGCM). The two warming scenarios are based on the Representative Concentration Pathways (RCPs) 2.6 and 8.5 from the Coupled Model Intercomparison Project phase 5 (CMIP5). Previously published studies show that the FSU...
Show moreThe effects of two different future warming climate scenarios on Global and North Atlantic named tropical cyclone (NTC) activity is examined using the Florida State University/Center for Ocean-Atmospheric Prediction Studies (FSU/COAPS) atmospheric general circulation model (AGCM). The two warming scenarios are based on the Representative Concentration Pathways (RCPs) 2.6 and 8.5 from the Coupled Model Intercomparison Project phase 5 (CMIP5). Previously published studies show that the FSU/COAPS AGCM has statistically significant skill at reproducing the observed interannual variability of NTC and hurricane counts in the North Atlantic basin given observed sea surface temperatures (SSTs). In this study, the FSU/COAPS model is forced with monthly varying annual climatological bias-corrected SSTs derived from the CCSM4 model's RCP2.6 and RCP8.5 simulations. In addition, the model's CO2 concentration is modified to reflect the average CO2 concentration over the 2006&ndash2100 time period. For each warming experiment, a 14 member ensemble is made to develop the NTC statistics. In addition, a 14 member control experiment is performed using observed climatological SSTs from the Hadley Centre. An objective detection/tracking algorithm is used to identify and track the NTCs from the model output. For the North Atlantic, a statistically significant increase (14.9%) in the NTC frequency for the RCP2.6 scenario compared to the control experiment is projected by the model. It is also found that with increasing SSTs and CO2 concentration, the North Atlantic NTC intensity (as determined by the NTC maximum 10-m wind speed) and daily storm-centered precipitation also increase. NTC genesis is found to move away from regions of increasing vertical wind shear and decreasing mid-level relative humidity for both future warming climate scenarios. Differences in the track densities between the warming experiments with the control experiment show an increase in landfall potential in the Southeast United States.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8885
Format: Thesis

Title: Estimate of Tropical Cyclone Parameters Based on Microwave Humidity Sounders.
Creator: Shi, Qi, Zou, Xiaolei, Cai, Ming, Wu, Zhaohua, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: TC structures consisting of eye, eyewall and rainband can be clearly resolved by Microwave Humidity Sounder (MHS) window channels. High brightness temperatures are found in cloud-free hurricane eye and cloud streaks, and low brightness temperatures are found in cloud rainbands. In this study, MHS is used to estimate TC center and radius of maximum wind. The TC center location is determined by the warmest brightness temperature of MHS channel 2 within TC eyewall region. The radius of maximum...
Show moreTC structures consisting of eye, eyewall and rainband can be clearly resolved by Microwave Humidity Sounder (MHS) window channels. High brightness temperatures are found in cloud-free hurricane eye and cloud streaks, and low brightness temperatures are found in cloud rainbands. In this study, MHS is used to estimate TC center and radius of maximum wind. The TC center location is determined by the warmest brightness temperature of MHS channel 2 within TC eyewall region. The radius of maximum wind is estimated based on the radial profiles brightness temperatures calculating at six-degree azimuthal angles. The shortest distance between the hurricane center and the minimum point of brightness temperature with some minimum points on its neighboring radial profiles is taken as the estimate of the radius of maximum wind. This method for estimating the TC center location and the radius of maximum wind was applied to twelve arbitrarily selected TCs that occurred in 2010, 2011 or 2012 over Atlantic basin. More than 78% of cases have the differences of TC center location and radius of maximum wind between MHS and NHC being less than 15 km and 10 km, respectively. The infrared observations from Advanced Very High Resolution Radiometer (AVHRR) on board the same satellite as MHS are also used for further comparison. It was found that the large differences between MHS estimate and Best Track analysis seem to occur for TCs with asymmetric structure or high-latitude locations.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8887
Format: Thesis

Title: Octocorals of Alaska: Comparing Morphologic and Genetic Methods of Community Composition Analysis.
Creator: Labelle, Benjamin, Baco-Taylor, Amy, MacDonald, Ian, Landing, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Seamounts are one of the largest biomes on earth, yet remain one of the least explored. They are known to be centers of increased biomass, species richness, endemism and speciation as well as areas of distinct community structure, as compared to surrounding areas. Much of this species richness may be due to the presence of structure-forming, deep-water corals on many seamounts. These corals act as ecosystem engineers, altering the local environment to the benefit of many other species. This...
Show moreSeamounts are one of the largest biomes on earth, yet remain one of the least explored. They are known to be centers of increased biomass, species richness, endemism and speciation as well as areas of distinct community structure, as compared to surrounding areas. Much of this species richness may be due to the presence of structure-forming, deep-water corals on many seamounts. These corals act as ecosystem engineers, altering the local environment to the benefit of many other species. This is especially true in the waters of Alaska, where octocorals, the dominant deep water corals, form dense assemblages known as "coral gardens". Alaska is home to a 5.8 billion dollar commercial fishing industry, and 85% of commercially fished species have been shown to associate with structure-forming invertebrates. Octocorals, however, are very vulnerable to disturbance events from bottom contact fishing gear. It is therefore imperative that we understand the connectivity, community composition and distribution of octocoral species in Alaska. Both traditional morphological species identification and DNA barcoding techniques have been employed to study octocoral communities, but each method has serious issues when used with octocorals, and it is currently unclear how the two methods compare. Here I utilize a large dataset of Alaskan octocorals, covering a wide range of the Alaskan coast and the Gulf of Alaska, to show that genetic methods of study reveal community structure not identified by methods utilizing morphologic species designations. Analysis was performed on parallel datasets of specimens - one featuring species designations made using traditional morphological taxonomic methods and one featuring species designations made using a 3-gene barcode method - in order to increase the state of knowledge regarding Alaskan octocoral distributions and community structure, as well as to compare the results of these two widely used methods. Communities were shown to be distinct on a province level, with the Aleutian Island sites, the seamount sites and the slope sites each forming separate communities. The 3-gene barcode method also identified a distinct deep community that the morphologic methods failed to distinguish. Depth was found to be the strongest structuring gradient for all datasets. This work yields new insight into the connectivity of Alaskan octocorals and suggests that they may need to be managed in a 3-dimensional manner, taking depth into account when protecting this vital fisheries habitat.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8828
Format: Thesis

Title: Investigations of the Ecology of Calcareous Nannoplankton and Nannofossils in the North-East Gulf of Mexico to Help Establish a Baseline for Environmental Impact Studies.
Creator: Agbali, Aisha, Wise, Sherwood W., Keller, Laura R., Wang, Yang, Chanton, Jeffrey, Kish, Stephen, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study presents for the first time, ecological relationships between coccolithophores and environmental conditions in the northeastern Gulf of Mexico. Cell densities of coccolithophores were determined in 598 samples taken from approximately thirty stations along three north-south trending transects at different depths within 0 to 200 m in the photic zone of the study area. An investigation of the absolute abundance of nannofossils in sediment cores taken from two sites in the DeSoto...
Show moreThis study presents for the first time, ecological relationships between coccolithophores and environmental conditions in the northeastern Gulf of Mexico. Cell densities of coccolithophores were determined in 598 samples taken from approximately thirty stations along three north-south trending transects at different depths within 0 to 200 m in the photic zone of the study area. An investigation of the absolute abundance of nannofossils in sediment cores taken from two sites in the DeSoto Canyon was also carried out. The main coccolithophore (mostly Emiliania huxleyi) production was observed within the top 60 m of the water column. The coccolithophores tend to reach maximum abundances in the upper photic zone and were least abundant in the lower photic zone. The average cell density throughout the study period was 41,524 cells per liter. Highest cell density recorded was 412,183 cells per liter in April 2013 in the upper photic zone. Florisphaera profunda accounted for cell density peaks below 75 m down to 125 m water depth. Coccolith cell production decreased drastically below 100 m water depth. A total of 104 coccolithophore species were identified. The assemblages were dominated by E. huxleyi, Gephyrocapsa ericsonii, Florisphaera profunda, Umbellosphaera tenius, Calciopappus rigidus and Michaelsarsia elegans. These taxa individually or together comprised more than 75% of the total assemblages in more than 90 percent of the samples. Gephyrocapsa oceanica, Ophiaster formosus, Calciosolenia murrayi, the Syracosphaera species, and the holococcoliths were the next most common taxa. The coccolithophore cell densities showed vertical and lateral variations as well as seasonal and inter-annual changes in abundance, diversity, and distribution during the study period. These variations were mainly related to changes in the thickness of the mixed-layer and the pycnocline. The coccolithophore cell densities and cell density variability of the dominant taxa were compared with in-situ measurements of temperature, salinity, chlorophyll, oxygen, nitrate and phosphorus to show the effects of the water column parameters on the cell densities. The results revealed the presence of distinct species groupings and distinct ecological preference of the groups. Coccolithophore cell densities and those of the dominant taxa were mostly influenced by temperature and phosphorus especially in the upper photic zone and nitrate and salinity in the lower photic zone. The assemblage compositions and abundances in the water and the sediments differ significantly.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8926
Format: Thesis

Title: An Analysis of Climate Feedback Contributions to the Land/Sea Warming Contrast.
Creator: Albert, Oriene S., Cai, Ming, Sura, Phillip, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The land/sea warming contrast being greater than unity is a well-known phenomenon in response to anthropogenic radiative forcing. The land/sea surface warming asymmetry is essentially a result of the differing surface and boundary layer properties over the land and ocean as well as the differing cloud feedbacks. In this study, we analyze the surface temperature response over the land and ocean, using the NCAR CCSM4, to a transient 1% yr-1 CO2 increase at the time of the doubling. The...
Show moreThe land/sea warming contrast being greater than unity is a well-known phenomenon in response to anthropogenic radiative forcing. The land/sea surface warming asymmetry is essentially a result of the differing surface and boundary layer properties over the land and ocean as well as the differing cloud feedbacks. In this study, we analyze the surface temperature response over the land and ocean, using the NCAR CCSM4, to a transient 1% yr-1 CO2 increase at the time of the doubling. The contributions of the external forcing (CO2) alone and various feedbacks are diagnosed using the Climate Feedback Response Analysis Method (CFRAM). This study found that the external forcing warms the land and ocean surfaces approximately the same, which suggests that the feedbacks are responsible for the warming contrast. Furthermore, this analysis confirms that the principal contributor to the above-unity land-to-sea warming ratio is the evaporation feedback; however, the results also indicate that the sensible heat flux feedback, which favors a greater warming for the ocean, has the largest land/sea warming difference. Consequently, the findings uniquely highlight the importance of other feedbacks in establishing the above-unity land-to-sea warming ratio. Specifically, the cloud and ocean dynamics/heat storage feedbacks are key contributors to the maintenance of the land/sea warming asymmetry. The results of this study provide a more holistic understanding of the climate feedbacks and their significance to the land and ocean temperature responses, when the climate is forced.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8929
Format: Thesis

Title: Detection of Radio Frequency Interference over Ocean.
Creator: Tian, Xiaoxu, Zou, Xiaolei, Wu, Zhaohua, Ray, Peter S., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The geostationary satellite television (TV) signals that are reflected off the ocean surfaces could enter the AMSR-E antenna, resulting in RFI (Radio Frequency Interference) contamination in AMSR-E 10.65 and 18.7 GHz channels. If not detected, the presence of RFI signals can result in false retrievals of oceanic environmental parameters (e.g., sea surface temperature, sea surface wind speed, rain water path) from microwave imaging radiance measurements. This study first examined the geometric...
Show moreThe geostationary satellite television (TV) signals that are reflected off the ocean surfaces could enter the AMSR-E antenna, resulting in RFI (Radio Frequency Interference) contamination in AMSR-E 10.65 and 18.7 GHz channels. If not detected, the presence of RFI signals can result in false retrievals of oceanic environmental parameters (e.g., sea surface temperature, sea surface wind speed, rain water path) from microwave imaging radiance measurements. This study first examined the geometric relationship between the RFI source, geostationary TV satellite, and AMSR-E observation. Then a normalized Principal Component Analysis (NPCA) method is proposed and applied for RFI detection over oceans in Advanced Microwave Scanning Radiometer (AMSR)-E observations. It is found that the RFI-contaminated observations on AMSR-E descending node at 10.65 and 18.7 GHz can be successively detected near coastal areas surrounding Europe and United States continents. The results yielded from the geometric examination at another angle verify those signals detected with NPCA. The proposed NPCA algorithm is applicable in an operational environment for fast data processing and data dissemination, and is different from earlier methods, which often require a priori information.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8901
Format: Thesis

Title: Global Ice Cloud Properties and Their Radiative Effects: Satellite Observations and Radiative Transfer Modeling.
Creator: Hong, Yulan, Liu, Guosheng, Ellingson, Robert R., Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Ice clouds play an important role in earth radiation balance by reflecting solar and absorbing thermal radiation, the so-called albedo versus greenhouse eects, which cause signicant dierential atmospheric heating and cooling in horizontal as well as vertical directions. Two active sensors onboard A-train satellites, CloudSat radar and CALIPSO lidar, for the rst time provide global proles of atmospheric ice clouds. A combination of radar and lidar becomes the state-of-the-art technique...
Show moreIce clouds play an important role in earth radiation balance by reflecting solar and absorbing thermal radiation, the so-called albedo versus greenhouse eects, which cause signicant dierential atmospheric heating and cooling in horizontal as well as vertical directions. Two active sensors onboard A-train satellites, CloudSat radar and CALIPSO lidar, for the rst time provide global proles of atmospheric ice clouds. A combination of radar and lidar becomes the state-of-the-art technique examining clouds of varying optical depth, as the former excels in probing thick clouds while the later is better suited to the thin ones. In this study, ice cloud properties derived by a combination of CloudSat and CALIPSO observations are adopted to character atmospheric ice clouds. Ice cloud climatological studies show that the global mean optical depth and eective radius are around 4 and 48 &mu m, respectively. Mean ice water path is approximately 110 g/m2 for all measurements and approximately 190 g/m2 for cloudy situations (conditional mean). Their occurrence frequencies and ice mass amount distributions do not just depend on their optical depth values, but also rely on seasons and day-night cycle. Meanwhile, ice water content and eective radius show dierent temperature dependent relationships among the tropics, mid- and high-latitudes. Ice cloud radiative eects are obtained by radiative transfer modelling. Simulations show global ice clouds net eects at the top of atmosphere (TOA) may slightly heat or cool the atmosphere-earth system depending on model parameterizations and allowing for uncertainties. Additionally, a cloud forcing spectrum over optical depth at the TOA shows that ice clouds with optical depth <5 display a positive net forcing on a global scale, inducing a warming eect, whereas ice clouds otherwise tend to be cooling. Regionally, ice clouds have a negative net forcing in the mid-latitude warm seasons due to a stronger solar albedo eect but a positive net forcing during cold seasons due to a stronger greenhouse eect. Moreover, ice cloud internal heating rate proles in the atmosphere indicate shortwave heating above but cooling below, whereas the longwave heating pattern is oppositive. This heating structure is regionally and seasonally dependent, and it is associated with optical depth values as well.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8807
Format: Thesis

Title: An Objective Regional Cloud Mask Algorithm for GOES Infrared Imager with Regime-Dependent Thresholds for Direct Radiance Assmilation.
Creator: Da, Cheng, Zou, Xiaolei, Liu, Guosheng, Ellingson, Robert G., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A local, regime-dependent cloud mask (CM) algorithm is developed for isolating cloud-free pixels from cloudy pixels for Geostationary Operational Environmental Satellite (GOES) imager radiance assimilation using mesoscale forecast models. In this CM algorithm, thresholds for six different CM tests are determined by a one-dimensional optimization approach based on probability distribution functions of the nearby cloudy and clear-sky pixels within a 10o×10o box centered at a target pixel. It is...
Show moreA local, regime-dependent cloud mask (CM) algorithm is developed for isolating cloud-free pixels from cloudy pixels for Geostationary Operational Environmental Satellite (GOES) imager radiance assimilation using mesoscale forecast models. In this CM algorithm, thresholds for six different CM tests are determined by a one-dimensional optimization approach based on probability distribution functions of the nearby cloudy and clear-sky pixels within a 10o×10o box centered at a target pixel. It is shown that the optimized thresholds over land are in general larger and display more spatial variations than over ocean. The performance of the proposed CM algorithm is compared with Moderate Resolution Imaging Spectroradiometer (MODIS) CM for a one-week period from 19 to 23 May 2008. Based on MODIS CM results, the average Probability of Correct Typing (PCT) reaches 92.94% and 91.50% over land and ocean, respectively.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-8763
Format: Thesis

Title: Radial-Vertical Profiles of Tropical Cyclone Derived from Dropsondes.
Creator: Ren, Wei, Cai, Ming, Misra, Vasubandhu, Sura, Philip, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Abstract/Description: The scopes of this thesis research are two folds: the first one is to the construct the intensity-based composite radial-vertical profiles of tropical cyclones (TC) using GPS-based dropsonde observations and the second one is to identify the major deficiencies of Mathur vortices against the dropsonde composites of TCs. The intensity-based dropsonde composites of TCs advances our understanding of the dynamic and thermal structure of TCs of different intensity along the radial direction in and...
Show moreThe scopes of this thesis research are two folds: the first one is to the construct the intensity-based composite radial-vertical profiles of tropical cyclones (TC) using GPS-based dropsonde observations and the second one is to identify the major deficiencies of Mathur vortices against the dropsonde composites of TCs. The intensity-based dropsonde composites of TCs advances our understanding of the dynamic and thermal structure of TCs of different intensity along the radial direction in and above the boundary layer where lies the devastating high wind that causes property damages and storm surges. The identification of the major deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity helps to improve numerical predictions of TCs since most operational TC forecast models need to utilize bogus vortices, such as Mathur vortices, to initialize TC forecasts and simulations. We first screen all available GPS dropsonde data within and round 35 named TCs over the tropical Atlantic basin from 1996 to 2010 and pair them with TC parameters derived from the best-track data provided by the National Hurricane Center (NHC) and select 1149 dropsondes that have continuous coverage in the lower troposphere. The composite radial-vertical profiles of tangential wind speed, temperature, mixing ratio and humidity are based for each TC category ranging from "Tropical Storm" (TS) to "Hurricane Category 1" (H1) through "Hurricane Category 5" (H5). The key findings of the dropsonde composites are: (i) all TCs have the maximum tangential wind within 1 km above the ground and a distance of 1-2 times of the radius of maximum wind (RMW) at the surface; (ii) all TCs have a cold ring surrounding the warm core near the boundary layer at a distance of 1-3 times of the RMW and the cold ring structure gradually diminishes at a higher elevation where the warm core structure prevails along the radial direction; (iii) the existence of such shallow cold ring outside the RMW explains why the maximum tangential wind is within 1 km above the ground and is outside the RMW, as required by the hydrostatic and gradient wind balance relations; (iv) one of the main differences among TCs of different intensity, besides the speed of the maximum tangential wind, is the vertical extent of near-saturated moisture air layer inside the core. A weaker TC tends to have a deep layer of the near-saturated moisture air layer whereas a stronger TC has a shallow one; (v) another main difference in the thermal structure among TCs of different intensity is the intensity and vertical extent of the warm core extending from the upper layer to the lower layer. In general, a stronger TC has a stronger warm core extending downward further into lower layer and vice versa. The features (iv) and (v) are consistent with the fact that a stronger TC tends to have stronger descending motion inside the core. The main deficiencies of Mathur vortices in representing the radial-vertical profiles of TC of different intensity are (i) Mathur vortices of all categories have the maximum wind at the surface; (ii) none of Mathur vortices have a cold ring outside the warm core near the boundary layer; (iii) Mathur vortices tend to overestimate warm core structure in reference to the horizontal mean temperature profile; (iv) Mathur vortices tend to overestimate the vertical depth of the near-saturated air layer near the boundary layer.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9235
Format: Thesis

Title: The Influence of Mesoscale Sea Surface Temperature Gradients on Tropical Cyclones.
Creator: Glazer, Russell Henderson, Bourassa, Mark A., Hart, Robert Edward, Powell, Mark Dillon, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of...
Show moreGlazer, Russell Henderson, Bourassa, Mark A., Hart, Robert Edward, Powell, Mark Dillon, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
Show less
Abstract/Description: The effects of mesoscale (50-1000km) sea surface temperature (SST) variability on tropical cyclones (TCs) are investigated with model simulations of an idealized TC as well as simulations of Hurricane Igor (2010) using the Weather Research and Forecasting (WRF) model. Mesoscale SST gradients significantly modify the surface wind speed and direction leading to areas of enhanced divergence/convergence and curl along the gradient. This paper explores the effects that these interactions between...
Show moreThe effects of mesoscale (50-1000km) sea surface temperature (SST) variability on tropical cyclones (TCs) are investigated with model simulations of an idealized TC as well as simulations of Hurricane Igor (2010) using the Weather Research and Forecasting (WRF) model. Mesoscale SST gradients significantly modify the surface wind speed and direction leading to areas of enhanced divergence/convergence and curl along the gradient. This paper explores the effects that these interactions between mesoscale SST gradients and the atmosphere have on TCs. In these idealized simulations it is shown that an SST gradient of similar scale to the idealized TC vortex produces asymmetry in the eyewall convection and leads to vertical misalignment of the vortex. Simulations of Igor are conducted with three different SST setups: a run with an unaltered SST field, a run with increased SST gradients, and a run with decreased SST gradients. Igor's intensity and structure is found to be sensitive to the three different SST setups but the specific mechanism could not be identified. It is found that the magnitude of moisture advection increases with increasing SST gradient magnitude on the warm side of a gradient.
Show less
Date Issued: 2014
Identifier: FSU_migr_etd-9177
Format: Thesis

Theses and Dissertations (245)	+ -
Undergraduate Honors Theses (19)	+ -

Oceanography (232)	+ -
Meteorology (144)	+ -
Earth sciences (118)	+ -
Geophysics (111)	+ -
Atmospheric physics (13)	+ -

Climatic changes (4)	+ -
Climate (3)	+ -
Atmospheric chemistry (2)	+ -
Geography (2)	+ -
Remote sensing (2)	+ -
Biogeochemistry (1)	+ -
Data processing (1)	+ -
Fresh water (1)	+ -
Longitudinal method (1)	+ -
Probabilities (1)	+ -
Time-series analysis (1)	+ -

text (264)	+ -
doctoral thesis (6)	+ -
master thesis (3)	+ -

Florida State University (245)	+ -
Department of Earth, Ocean and Atmospheric Sciences (228)	+ -
Liu, Guosheng (45)	+ -
Hart, Robert (39)	+ -
Sura, Philip (30)	+ -

Search In

Pages

Pages

Sort Results By:

Narrow results by:

Collection

Topical Subject

Genre

Type of Resource

Language

Creator

Owner