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Title: High-resolution satellite surface latent heat fluxes in North Atlantic hurricanes.
Creator: Liu, Jiping, Curry, Judith A., Clayson, Carol Anne, Bourassa, Mark
Abstract/Description: This study presents a new high-resolution satellite-derived ocean surface flux product, XSeaFlux, which is evaluated for its potential use in hurricane studies. The XSeaFlux employs new satellite data sets using improved retrieval methods, and uses a new bulk flux algorithm formulated for high wind conditions. The XSeaFlux latent heat flux (LHF) performs much better than the existing numerical weather prediction reanalysis and satellite-derived flux products in a comparison with measurements...
Show moreThis study presents a new high-resolution satellite-derived ocean surface flux product, XSeaFlux, which is evaluated for its potential use in hurricane studies. The XSeaFlux employs new satellite data sets using improved retrieval methods, and uses a new bulk flux algorithm formulated for high wind conditions. The XSeaFlux latent heat flux (LHF) performs much better than the existing numerical weather prediction reanalysis and satellite-derived flux products in a comparison with measurements from the Coupled Boundary Layer Air-Sea Transfer (CBLAST) field experiment. Also, the XSeaFlux shows well-organized LHF structure and large LHF values in response to hurricane conditions relative to the other flux products. The XSeaFlux data set is used to interpret details of the ocean surface LHF for selected North Atlantic hurricanes. Analysis of the XSeaFlux data set suggests that ocean waves, sea spray, and cold wake have substantial impacts on LHF associated with the hurricanes.
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Date Issued: 2011
Identifier: FSU_migr_coaps_pubs-0023, 10.1175/2011MWR3548.1
Format: Citation

Title: Effect of Stratification and Background Flow on the Frequency of Rossby Basin Modes in Presence of Bottom Topography.
Creator: Colantuono, Giuseppe, Dewar, William, Chassignet, Eric, Clayson, Carol Anne, Program in Geophysical Fluid Dynamics, Florida State University
Abstract/Description: This work attempts to express the change, induced by the introduction of stratification, of the Rossby eigen-modes of a closed basin with bottom topography, filled with a uniform fluid in the unperturbed configuration. Such a modification has been found in the output of a set of numerical experiments on the Argentine Basin and then computed analytically: stratification has been introduced in the mathematical form of a perturbation of a homogeneous fluid over a non flat bottom. It has been...
Show moreThis work attempts to express the change, induced by the introduction of stratification, of the Rossby eigen-modes of a closed basin with bottom topography, filled with a uniform fluid in the unperturbed configuration. Such a modification has been found in the output of a set of numerical experiments on the Argentine Basin and then computed analytically: stratification has been introduced in the mathematical form of a perturbation of a homogeneous fluid over a non flat bottom. It has been found that the eigen-modes lose their barotropic character and differences appear in the dynamical fields (velocity and pressure) from upper to lower layer. Moreover, the frequency of the modes changes; an analytical expression of this frequency correction as a function of stratification has been found. The impact on modal frequency of a geostrophic background flow has also been computed analytically. Some simple analytical results for an elementary geometrical setting have been determined.
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Date Issued: 2009
Identifier: FSU_migr_etd-3567
Format: Thesis

Title: A Numerical Investigation of the Impact of Ice Hydrometeors on the Intensity of Hurricane Isabel.
Creator: Sheermohamed, Jordanna, Krishnamurti, T. N., Hart, Robert, Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The goal of this study is to further investigate the relationship between the microphysical processes of a tropical cyclone and its intensification. Hydrometeors such as rainwater, cloud ice, cloud water, snow, and graupel play a significant role updraft and downdraft characteristics, precipitation, evaporation, ice concentration, and the distribution of latent heat. These processes are the primary heat sources for tropical cyclones. Therefore, it is expected that cloud microphysics may...
Show moreThe goal of this study is to further investigate the relationship between the microphysical processes of a tropical cyclone and its intensification. Hydrometeors such as rainwater, cloud ice, cloud water, snow, and graupel play a significant role updraft and downdraft characteristics, precipitation, evaporation, ice concentration, and the distribution of latent heat. These processes are the primary heat sources for tropical cyclones. Therefore, it is expected that cloud microphysics may directly or indirectly influence the intensity of the hurricane. The first objective of this study is to evaluate the impact of different sophisticated explicit cloud microphysics parameterization schemes available in the PSU/NCAR MM5 model, on the hurricane forecast. Of the four microphysical parameterization schemes, the one that exhibited an intensity pattern closely resembling that of the observed values for the hurricane was selected in order to continue onto the next phase of the project. The second objective is to assess the impact of ice hydrometeors (cloud ice), in the overall performance of the hurricane forecast. This phase further investigates the impact of the selected microphysical processes on the overall forecast of the hurricane, with an emphasis on intensity. This is achieved by suppressing some of the microphysical processes that would allow for ice depletion. By doing so, we indirectly increase the amount of ice in the hurricane. This numerical comparison is done in the selected scheme both before and after ice production terms are modified, in order to substantiate the hypothesis whether or not an increased amount of ice in a tropical cyclone would lead to a more intense storm.
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Date Issued: 2005
Identifier: FSU_migr_etd-1782
Format: Thesis

Title: Impact of Airborne Dust on Sea Surface Temperature Retrievals.
Creator: Bogdanoff, Alec Setnor, Clayson, Carol Anne, Bourassa, Mark A., Liu, Guosheng, Westphal, Douglas L., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Sea Surface Temperatures (SSTs) are an important measure of our current weather and climate, as well as an essential variable in both short and long term weather forecasting. Infrared SST retrievals are reliant on passive sensors, and retrieval techniques are influenced by changes in atmospheric composition, including aerosols. Many empirically derived retrieval algorithms are based on matching Top of Atmosphere (TOA) Brightness Temperatures (BTs) from the Advanced Very High Resolution...
Show moreSea Surface Temperatures (SSTs) are an important measure of our current weather and climate, as well as an essential variable in both short and long term weather forecasting. Infrared SST retrievals are reliant on passive sensors, and retrieval techniques are influenced by changes in atmospheric composition, including aerosols. Many empirically derived retrieval algorithms are based on matching Top of Atmosphere (TOA) Brightness Temperatures (BTs) from the Advanced Very High Resolution Radiometer (AVHRR) to buoy measurements during clear-sky conditions. Data is cloud-cleared to remove cloud-contaminated data. However, small, but influential, Aerosol Optical Depths (AODs) data may not be flagged as contaminated and the algorithms incorrectly calculate a cold SST due to the radiometer sensing the cooler, elevated aerosol layer temperature. Many studies on aerosol effects on SSTs focus on aerosols due to volcanic eruptions. However, truly operational tropospheric aerosol corrections for daytime and nighttime retrievals have yet to be implemented. This work constitutes a first step to creating an accurate aerosol correction by exploring the sensitivity of aerosols on SSTs. The Santa Barbra DISORT Radiative Transfer model is used to quantify the effects of aerosol contamination on retrieved TOA BTs. The calculated radiances are spectrally averaged over each channel, converted to BTs, and used to calculate an SST using the Naval Oceanographic Office AVHRR algorithms. A radiative transfer model is used to evaluate the SST retrieval error due to varying AOD, height of an aerosol layer, and the satellite zenith angle (or viewing angle). This analysis shows that errors greater than the stated retrieval uncertainty of 0.5 K are observed for AODs greater than 0.25. Two sites with state-of-the-art aerosol measurements are analyzed for AOD variability. The first site, at Anmyon in east Asia, is found to have 14% of the days during the springtime with an AOD greater than 0.25. Based on the AERONET data from a second site in Cape Verde, 65% of the days during the boreal summer are found to have AOD greater than 0.25. Unfortunately, this seasonal peak in dust activity coincides with the active tropical cylogensis season for the region, making accurate SSTs even more vital for prediction purposes.
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Date Issued: 2010
Identifier: FSU_migr_etd-3629
Format: Thesis

Title: An Investigation on the Physical Mechanisms and Variability of the Australian Summer Monsoon.
Creator: Kullgren, Katherin, Kim, Kwang-Yul, Hart, Robert, Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: In order to understand the physical mechanisms of the Australian summer monsoon,cyclostationary EOF analysis was conducted on the 23-year (1979-2002) Xie- Arkin pentad summer precipitation data and other key physical variables over the Australian monsoon region,including the tropical and southern Indian and Pacific Oceans. The first mode of precipitation represents the El Niño signal, the second mode is the seasonal cycle, the third mode describes thephase transition of ENSO between El Niño...
Show moreIn order to understand the physical mechanisms of the Australian summer monsoon,cyclostationary EOF analysis was conducted on the 23-year (1979-2002) Xie- Arkin pentad summer precipitation data and other key physical variables over the Australian monsoon region,including the tropical and southern Indian and Pacific Oceans. The first mode of precipitation represents the El Niño signal, the second mode is the seasonal cycle, the third mode describes thephase transition of ENSO between El Niño and La Niña, and the fourth and fifth modes represent separate components of the Madden-Julian oscillations. All five modes together explain about1/3 of the total variance of the pentad precipitation data. The physical mechanisms of the seasonal cycle, which explains the "mean" seasonal evolution of the Australian summermonsoon in the absence of other external physical mechanisms, are identified. The onset and termination mechanisms of the Australian summer monsoon are stronglyassociated with the surface temperature changes over the Australian continent and the resulting sea level pressure (SLP) changes. Almost a month prior to the monsoon onset, the surfacetemperature over northern Australia increases and consequently SLP decreases. This initiates an cyclonic circulation over Australia. The increased upward motion induced by the surfacewarming together with the anomalous cyclonic circulation results in the increased lower-level moisture convergence over the interior of Australia. This increases the amount of precipitationover northern Australia and eventually starts the monsoon. In conjunction with the anomalous cyclonic circulation, zonal wind anomalies over northern Australia change from easterly towesterly. During the termination stage, physical conditions over Australia are reversed. Variability of the Australian monsoon onset, termination, and strength was alsoinvestigated in terms of the first five major modes of monsoon precipitation found via CSEOF analysis. Whereas the seasonal cycle defines the fixed onset (~January 5 ± 5 days) and termination (~March 5 ± 5 days) dates, the presence of other modes alters these dates. The impact of each mode was investigated after each mode was added to or subtracted from the meanseasonal cycle, each having a strength corresponding to one standard deviation of its variability. It is shown that the contribution of each mode to the monsoon precipitation is geographicallycomplex and varies significantly throughout the monsoon period. One striking feature is that the impact of each mode is highly asymmetric with respect to its phase. The negative modes generally affect more significantly the onset, the termination, and the amount of monsoonprecipitation. Although each of the four modes make a unique and tangible contribution, the ENSO mode contributes most significantly to the overall mean and variance of the monsoonprecipitation variability. While the positive ENSO (El Niño) mode does not seriously alter the onset and termination times, the negative ENSO (La Niña) mode prolongs the duration of the Australian summer monsoon significantly. Although the contribution to the overall mean is small, the two MJO modes are the most dominating factor controlling the onset and terminationtimes of the Australian summer monsoon.
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Date Issued: 2006
Identifier: FSU_migr_etd-2975
Format: Thesis

Title: The Impact of Marine Cold-Air Outbreaks on the Rate of Oceanic Heat Storage in the Gulf of Mexico.
Creator: Hunniford, Rebecca, Clayson, Carol Anne, Hart, Robert, Nof, Doron, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The Gulf of Mexico is among the most populated of coastlines threatened by tropical cyclones and has experienced some of the most destructive hurricanes in history. The importance of the warm ocean waters of the Gulf in providing optimal conditions for tropical cyclone intensification is becoming more clear with recent research; thus, understanding factors that affect the upper ocean heat content in the Gulf is essential to anticipating hurricane intensity. In this study, two reanalysis data...
Show moreThe Gulf of Mexico is among the most populated of coastlines threatened by tropical cyclones and has experienced some of the most destructive hurricanes in history. The importance of the warm ocean waters of the Gulf in providing optimal conditions for tropical cyclone intensification is becoming more clear with recent research; thus, understanding factors that affect the upper ocean heat content in the Gulf is essential to anticipating hurricane intensity. In this study, two reanalysis data sets, NASA's Modern Era Retrospective-analysis for Research Applications (MERRA) and the NCEP Climate Forecast System Reanalysis (CFSR), are used to calculate the surface heat flux budget and the upper ocean heat budget of the Gulf for 29 winter seasons (November – March), since the greatest spatial and temporal variability in the surface fluxes occurs during this season. The results of the heat budget analysis indicate that the turbulent fluxes largely drive the magnitude and the interannual variability of the rate of oceanic heat storage. Marine cold-air outbreaks (CAOs) bring cold, dry polar air over the Gulf throughout the winter season, forcing the release of extreme latent and sensible heat fluxes from the ocean to the atmosphere. To understand the impact of these events on the interannual variability in the rate of oceanic heat storage, we create a climatology of CAO event characteristics for 29 winter seasons. We find that on average, over half of the total winter season flux loss occurs due to surface fluxes during CAO events, the duration of which only accounts for about 15% of the winter season. Therefore, capturing the heat flux loss due to these events is essential to accurately determining the rate of change in upper ocean heat content throughout the winter season, as well as during the ensuing months. The possible impact of this extreme winter season heat flux loss on the following hurricane season is explored on a preliminary basis through comparison of the interannual variability in the July average upper ocean heat content to that of the CAO heat flux loss. My results suggest that the heat flux loss due to CAOs does affect the variability of the summer season ocean heat content. However, this variability is very small in comparison to the total ocean heat content. More in depth analysis must be done to better determine how long-lasting the effects of the winter season heat flux loss are, and to assess their influence on the thermal structure of the upper ocean during the hurricane season.
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Date Issued: 2011
Identifier: FSU_migr_etd-3400
Format: Thesis

Title: On Determining the Hurricane Boundary Layer.
Creator: Paget, Aaron Christopher, Ruscher, Paul, Krishnamurti, T. N., Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The hurricane boundary layer thickness as determined through the uniform constant BL depth model and varying prescribed BL depth model presented by Smith and Vogl (2008) is compared to the Troen and Mahrt (1986) method. Smith and Vogl presented the uniform constant BL depth approach from Emanual (1986) and a spatially varying prescribed BL depth based on inertial stability from the gradient wind. The Troen and Mahrt method of diagnosing the boundary layer thickness using the Richardson number...
Show moreThe hurricane boundary layer thickness as determined through the uniform constant BL depth model and varying prescribed BL depth model presented by Smith and Vogl (2008) is compared to the Troen and Mahrt (1986) method. Smith and Vogl presented the uniform constant BL depth approach from Emanual (1986) and a spatially varying prescribed BL depth based on inertial stability from the gradient wind. The Troen and Mahrt method of diagnosing the boundary layer thickness using the Richardson number is a basis for the Hong and Pan or MRF boundary layer schemes available in many hurricane models including WRF and MM5. .Hurricane Isabel (2003) is analyzed from dropwindsondes and GFDL model output. An additional hurricane, developed in the CM1 without a specified boundary layer formulation, is analyzed for comparing methods in determining the boundary layer thickness. The in situ observations did not lead to any conclusive results, however the modeled environments did show patterns in the boundary layer depth which support a spatially varying depth. The inertial stability method and the Troen and Mahrt method of determining the boundary layer thickness differed with depths increasing with increasing radius away from the radius of maximum wind for the inertial stability method and depths decreasing with increasing radius away from the radius of maximum wind with the Troen and Mahrt method.
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Date Issued: 2009
Identifier: FSU_migr_etd-2374
Format: Thesis

Title: Long-Term ENSO-Related Winter Rainfall Predictions over the Southeast U.S. Using the FSU Global Spectral Model.
Creator: Petraitis, Dawn C., O'Brien, James J., Clayson, Carol Anne, Jin, Fei-Fei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Rainfall patterns over the Southeast U.S. have been found to be connected to the El Niño-Southern Oscillation (ENSO). Warm ENSO events cause positive precipitation anomalies and cold ENSO events cause negative precipitation anomalies. With this level of connection, models can be used to test the predictability of ENSO events. Using the Florida State University Global Spectral Model (FSUGSM), model data over a 50-year period will be evaluated for its similarity to observations. The FSUGSM is a...
Show moreRainfall patterns over the Southeast U.S. have been found to be connected to the El Niño-Southern Oscillation (ENSO). Warm ENSO events cause positive precipitation anomalies and cold ENSO events cause negative precipitation anomalies. With this level of connection, models can be used to test the predictability of ENSO events. Using the Florida State University Global Spectral Model (FSUGSM), model data over a 50-year period will be evaluated for its similarity to observations. The FSUGSM is a global spectral model with a T63 horizontal resolution (approximately 1.875°) and 17 unevenly spaced vertical levels. Details of this model can be found in Cocke and LaRow (2000). The experiment utilizes two runs using the Naval Research Laboratory (NRL) RAS convection scheme and two runs using the National Centers for Environmental Prediction (NCEP) SAS convection scheme to comprise the ensemble. The simulation was done for 50 years, from 1950 to 1999. Reynolds and Smith monthly mean sea surface temperatures (SSTs) from 1950-1999 provide the lower boundary condition. Atmospheric and land conditions from January 1, 1987 and January 1, 1995 were used as the initial starting conditions. The observational precipitation data being used as the basis for comparison is a gridded global dataset from Willmott and Matsuura (2005). Phase precipitation differences show higher precipitation amounts for El Niño than La Niña in all model runs. Temporal correlations between model runs and the observations show southern and eastern areas with the highest correlation values during an ENSO event. Skill scores validate the findings of the model/observation correlations, with southern and eastern areas showing scores close to zero. Temporal correlations between tropical Pacific SSTs and Southeast precipitation further confirm the model's ability to predict ENSO precipitation patterns over the Southeast U.S. The inconsistency in the SST/precipitation correlations between the models can be attributed to differences in the 200-mb jet stream and 500-mb height anomalies. Slight differences in position and strength for both variables affect the teleconnection between tropical Pacific SSTs and Southeast.
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Date Issued: 2006
Identifier: FSU_migr_etd-1984
Format: Thesis

Title: A Global and Regional Diagnostic Comparison of Air-Sea Flux Parameterizations during Episodic Events.
Creator: Moroni, David Francis, Bourassa, Mark, Chassignet, Eric, Clayson, Carol Anne, Cunningham, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Twenty turbulent flux parameterizations are compared globally and regionally with a focus on the differences associated with episodic events. The regional focus is primarily upon the Gulf Stream and Drake Passage, as these two regions contain vastly different physical characteristics related to storm and frontal passages, varieties of sea-states, and atmospheric stability conditions. These turbulent flux parameterizations are comprised of six stress-related parameterizations [i.e., Large and...
Show moreTwenty turbulent flux parameterizations are compared globally and regionally with a focus on the differences associated with episodic events. The regional focus is primarily upon the Gulf Stream and Drake Passage, as these two regions contain vastly different physical characteristics related to storm and frontal passages, varieties of sea-states, and atmospheric stability conditions. These turbulent flux parameterizations are comprised of six stress-related parameterizations [i.e., Large and Pond (1981), Large et al. (1994), Smith (1988), HEXOS (Smith et al. 1992, 1996), Taylor and Yelland (2001), and Bourassa (2006)] which are paired with a choice of three atmospheric stability parameterizations ['Neutral' assumption, Businger-Dyer (Businger 1966, Dyer 1967, Businger et al. 1971, and Dyer 1974) relations, and Beljaars-Holtslag (1991) with Benoit (1977)]. Two remaining turbulent flux algorithms are COARE version 3 (Fairall et al. 2003) and Kara et al. (2005), where Kara et al. is a polynomial curve fit approximation to COARE; these have their own separate stability considerations. The following data sets were used as a common input for parameterization: Coordinated Ocean Reference Experiment version 1.0, Reynolds daily SST, and NOAA WaveWatch III. The overlapping time period for these data sets is an eight year period (1997 through 2004). Four turbulent flux diagnostics (latent heat flux, sensible heat flux, stress, curl of the stress) are computed using the above parameterizations and analyzed by way of probability distribution functions (PDFs) and RMS analyses. The differences in modeled flux consistency are shown to vary by region and season. Modeled flux consistency is determined both qualitatively (using PDF diagrams) and quantitatively (using RMS differences), where the best consistencies are found during near-neutral atmospheric stratification. Drake Passage shows the least sensitivity (in terms of the change in the tails of PDFs) to seasonal change. Specific flux diagnostics show varying degrees of consistency between stability parameterizations. For example, the Gulf Stream's latent heat flux estimates are the most inconsistent (compared to any other flux diagnostic) during episodic and non-neutral conditions. In all stability conditions, stress and the curl of stress are the most consistent modeled flux diagnostics. Sea-state is also a very important source of modeled flux inconsistencies during episodic events for both regions.
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Date Issued: 2008
Identifier: FSU_migr_etd-2261
Format: Thesis

Title: Improved Short-Term Atlantic Hurricane Intensity Forecasts Using Reconnaissance-Based Core Measurements.
Creator: Murray, David Andrew, Hart, Robert, Clayson, Carol Anne, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: While tropical cyclone (TC) track forecasting has improved noticeably over the last twenty years, intensity forecasting has remained somewhat of an enigma to forecasters. Despite increased computing capabilities and more sophisticated dynamical models, statistical models, such as the Statistical Hurricane Intensity Prediction Scheme (SHIPS), still often outperform their dynamical counterparts. There has been a great deal of research focused on improving intensity forecasts of TCs during the...
Show moreWhile tropical cyclone (TC) track forecasting has improved noticeably over the last twenty years, intensity forecasting has remained somewhat of an enigma to forecasters. Despite increased computing capabilities and more sophisticated dynamical models, statistical models, such as the Statistical Hurricane Intensity Prediction Scheme (SHIPS), still often outperform their dynamical counterparts. There has been a great deal of research focused on improving intensity forecasts of TCs during the past two decades. However, the overwhelming majority of this statistical research has focused on the impacts of the storm environment rather than the effects of the TC structure itself or inner-core measurements. More focus has been placed recently on using some of these measurements from within the TC core, such as the structure of the storm and reconnaissance flight data. Still, much work remains to be done to fully utilize the available data from the inner core of TCs. To this end, flight data from Hurricane Hunter reconnaissance missions will be exploited to the fullest extent in this study. This research seeks to develop a new statistical-climatological forecasting scheme to improve short-term intensity forecasts for well-developed TCs in the Atlantic basin. Well-developed TCs are classified in this study as having a defined eye. Using Vortex Data Messages (VDMs) gathered from the aforementioned reconnaissance flights and stored in the National Hurricane Center's (NHC) Automated Tropical Cyclone Forecast (ATCF) archives, a VDM climatology from 1991-2008 is developed. These VDMs are collected from dropsondes and include various structural and thermodynamic parameters. This climatology includes storm-scale thermodynamic parameters to aid in TC prediction. A new climatological forecast tool is produced which gives the expected rate of intensity change for 12-48 hour periods based on an initial eye diameter and wind speed. This climatological tool also provides insight into the dynamics involved in hurricane intensity change. Other implications based on the climatological forecast tool, such as the ability to produce probabilistic intensity range forecasts, are also discussed. Finally, stepwise multiple linear regression is performed to create a SHIPS-style intensity forecast model (Atlantic-based Statistical Prediction of Hurricane Intensity using Recon, or ASPIRE). Examination of the regression equations and the change in predictors selected with varying intensity and forecast length offers additional insight into the science of TC intensity forecasting. Cross-validation results show that the ASPIRE technique outperforms SHIPS at nearly every forecast time and initial intensity, indicating that a new benchmark for TC intensity forecasting may have been attained. Two dependent case studies of Hurricane Ivan and Hurricane Katrina are presented for further analysis of the ASPIRE technique. Further work involving the utilization of satellite data to create proxy VDMs may lead to an expanded climatological database of inner-core data for TCs in the Atlantic basin as well as the capability to create similar regression schemes in the East Pacific and West Pacific basins.
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Date Issued: 2009
Identifier: FSU_migr_etd-2165
Format: Thesis

Title: Evaluation of Surface Heat Flux Uncertainties and Their Impacts on the Study of Ocean Mixed Layer Temperature Variability.
Creator: Roberts, Jason Brent, Clayson, Carol Anne, Nof, Doron, Bourassa, Mark, Sura, Philip, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A major theme of recent research is the investigation of the nature of climate variability and the current capability to measure, model, and predict it. This is a formidable task that involves understanding complex interactions and exchanges of energy between the major elements of the Earth system. With their ability to store and release vast quantities of heat, the oceans are an integral element of climate variability. Accurately modeling coupled atmosphere-ocean variability relies upon a...
Show moreA major theme of recent research is the investigation of the nature of climate variability and the current capability to measure, model, and predict it. This is a formidable task that involves understanding complex interactions and exchanges of energy between the major elements of the Earth system. With their ability to store and release vast quantities of heat, the oceans are an integral element of climate variability. Accurately modeling coupled atmosphere-ocean variability relies upon a proper characterization of the exchanges of heat and momentum across the air-sea interface. The exchange of heat takes place through net shortwave and terrestrial radiative fluxes and turbulent exchanges of heat and moisture. Estimating these interactions with sufficient accuracy is a difficult challenge. These processes contain inherent errors due to insufficient knowledge of physics, observational uncertainty, and parameterization deficiencies. Uncertainties arising from the estimation of the surface turbulent and radiative processes generate limitations to the understanding of the primary mechanisms governing oceanic variability. This work elucidates the impact of uncertainties in the estimation of turbulent and radiative heat fluxes on the analysis of the mixed layer temperature balance, an effect that has not been properly quantified although recognized in most previous analyses. In particular, this work focuses on variability at seasonal and intraseasonal time scales. The analyses of this work include: i) an updated characterization of uncertainties in current state-of-the-art estimates of the turbulent and radiative heat fluxes, ii) an examination of the closure of the mixed layer temperature balance on seasonal and intraseasonal time scales, iii) an evaluation of the sensitivity of the mixed layer temperature balance to differences between surface heat flux estimates, iv) the development of a flexible approach by which to determine required accuracies of the net surface heat flux, and v) an exploration of the role of mixed layer depth variability on the mixed layer temperature balance. Taken together, the results of these analyses provide a framework to understand the impact of surface heat flux uncertainties within the context of upper ocean mixed layer variability. The analyses performed in this study have exploited a set of eight turbulent and six radiative heat flux estimates. An intercomparison of these products has revealed that the typical spread between products has been reduced relative to previous generations of estimates. Differences between radiative and turbulent heat flux estimates are typically within 15-20% of one another on regional and seasonal scales although larger uncertainties remain in traditionally problematic regions (e.g., cloud-topped boundary layers, western boundary currents). On both intraseasonal and seasonal time scales, the ocean mixed layer is controlled most strongly by the net shortwave and turbulent latent heat fluxes over the world oceans with the exception of the deep tropics wherein oceanic processes are also important. The current ensemble mean estimates of the net surface heat fluxes and oceanic process are capable of resolving the upper ocean mixed layer temperature seasonal cycle quite well in many locations; areas of strong net heat flux warming are somewhat problematic. On intraseasonal time scales, small signal to noise ratios and large residual imbalances leave little room to make definitive conclusions on the role of individual elements of mixed layer forcing. However, general features of the relative importance of surface heat flux variability versus oceanic variability are supported from previous studies. The mixed layer temperature balance is found to be most sensitive to uncertainties in the latent and net shortwave heat fluxes. The timing of the shoaling of the mixed layer depth is also important to the sensitivity of the mixed layer temperature balance. Taking into account mixed layer depth variability is found to be important to understanding the role of the net surface heat fluxes in generating mixed layer temperature warming and cooling. Current estimates of the net heat flux uncertainty are outside of the traditional 10 W m &minus 2 goal on seasonal time scales and spatial scales on the order of 1000 km. The approach designed within this investigation suggests that a 10 W m &minus 2 limit is somewhat too restricting if the aim is to resolve the seasonal mixed layer temperature evolution. In short, the use of the ocean mixed layer temperature balance has provided a unique framework for translating uncertainties in the surface heat flux estimates into a practical context. It is hoped that a better appreciation of these uncertainties will lead to an improved ability to model and understand the mechanisms by which the oceans contribute to variability of Earth's climate.
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Date Issued: 2011
Identifier: FSU_migr_etd-5144
Format: Thesis

Title: Effects of a Diurnal Sea Surface Temperature on Atmospheric Variability and Surface Fluxes.
Creator: Haman, Christine Lanier, Clayson, Carol Anne, Bourassa, Mark, Cunningham, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The Madden-Julian Oscillation (MJO) is a coupled air-sea interaction that dominates intraseasonal variability in the tropical oceans. This mode of variability is especially important in the tropical western Pacific Ocean warm pool because this region contains the warmest sea surface temperatures (SST), largest annual precipitation, and largest latent heat release in the atmosphere, which strongly affect the global redistribution of heat, moisture, and momentum. The MJO is difficult to...
Show moreThe Madden-Julian Oscillation (MJO) is a coupled air-sea interaction that dominates intraseasonal variability in the tropical oceans. This mode of variability is especially important in the tropical western Pacific Ocean warm pool because this region contains the warmest sea surface temperatures (SST), largest annual precipitation, and largest latent heat release in the atmosphere, which strongly affect the global redistribution of heat, moisture, and momentum. The MJO is difficult to reproduce in models, and some speculate it is because of the relationship between the MJO and diurnal SST variability (e.g. Zheng et al. 2004). A single-column coupled atmosphere-ocean model (SCCM) is used to calculate and evaluate the effects of diurnal SST variability on the marine boundary layer and convection during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean-Atmosphere Response Experiment (COARE) Intensive Observations Period (IOP). Results show that the use of a diurnally-varying SST as opposed to a daily-averaged SST impact the lower atmosphere by several degrees and the upper atmosphere through convection. Large-scale advective tendencies of air temperature and specific humidity can act to enhance or reduce the effects of local feedbacks resulting from diurnal warming. The absence of the diurnal SST cycle substantially impacts the transition phases of the MJO with considerable differences in low-level and mid-level cloud amount, due to changes in low-level moistening, which is essential in preconditioning the atmosphere for deep convection. These results support the hypothesis that a lack of diurnal SST variability in large-scale models could contribute to incorrect moistening during the transition phase, which is important to simulating the MJO.
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Date Issued: 2007
Identifier: FSU_migr_etd-4311
Format: Thesis

Title: PV-Induced Forcing of Gravity Waves in a Shallow Water Model.
Creator: Ward, Marshall, Cunningham, Philip, Peterson, Janet, Clayson, Carol Anne, Dewar, William K., Krishnamurti, Ruby, Program in Geophysical Fluid Dynamics, Florida State University
Abstract/Description: The influence of a geostrophically balanced or potential vorticity (PV) background flow on gravity wave propagation is examined using a rotating shallow water model. The system is analyzed in the context of a perturbative expansion that focuses on the dynamics of the resonances within the nonlinear terms of the system. The nonlinearity is reconstructed as a wave-wave interaction forcing on an otherwise undisturbed linear wavefield. The principal conclusion is that while the PV flow is...
Show moreThe influence of a geostrophically balanced or potential vorticity (PV) background flow on gravity wave propagation is examined using a rotating shallow water model. The system is analyzed in the context of a perturbative expansion that focuses on the dynamics of the resonances within the nonlinear terms of the system. The nonlinearity is reconstructed as a wave-wave interaction forcing on an otherwise undisturbed linear wavefield. The principal conclusion is that while the PV flow is generally undisturbed by the gravity wavefield, the gravity wavefield is forced by the geostrophic flow over moderate timescales. We numerically test these results for the interaction between a single geostrophic mode and a gravity wave, followed by propagation of a single gravity mode through a turbulent PV background. We find that the gravity mode energy is scattered into other modes of similar wavelength but different directions of propagation. The rate of dispersion is in agreement with resonant triad theory, where the rate depends primarily on the initial gravity wavenumber and background PV strength. These results are expected to have relevance to the propagation of coherent internal tides in the open ocean.}
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Date Issued: 2008
Identifier: FSU_migr_etd-1243
Format: Thesis

Title: Seasonal and Interannual Variability of Tropical Diurnal Warming of Sea Surface Temperatures.
Creator: Weitlich, Derrick, Clayson, Carol Anne, Bourassa, Mark, Krishnamurti, T. N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A method for determining the diurnal sea surface temperature (SST) cycle through satellite data has previously been developed by Clayson and Curry (1996). In their work they applied a parameterized equation from Webster et al. (1996) that uses the magnitude of peak solar insolation, the cumulative amount of daily precipitation, and average daily wind speed to compute the diurnal warming of SSTs. This parameterization has been applied to data obtained by the International Satellite Cloud...
Show moreA method for determining the diurnal sea surface temperature (SST) cycle through satellite data has previously been developed by Clayson and Curry (1996). In their work they applied a parameterized equation from Webster et al. (1996) that uses the magnitude of peak solar insolation, the cumulative amount of daily precipitation, and average daily wind speed to compute the diurnal warming of SSTs. This parameterization has been applied to data obtained by the International Satellite Cloud Climatology Project (ISCCP) and Special Sensor Microwave/Imager (SSM/I) data to produce a daily diurnal warming database for the global tropics during the years 1996-2000. Precipitation values were not yet available and were found to play a smaller role in diurnal warming, so they were not used in this study. Daily files of diurnal warming (dSST) were created at a spatial resolution of 0.25 deg. longitude x 0.25 deg. latitude. This study examines the spatial and temporal variability of dSST over the global tropics by examining averages of these values seasonally and year to year and by conducting an EOF analysis of the data for the tropical Atlantic, Indian, and Pacific Oceans. Results show that different atmospheric processes influence dSST for each tropical ocean basin. Also, dSST is shown to be driven by surface fluxes and not the underlying ocean characteristics. However, diurnal warming can affect the depth of mixing and entrainment cooling in the upper ocean by influencing the oceanic stability at the surface.
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Date Issued: 2005
Identifier: FSU_migr_etd-1201
Format: Thesis

Title: Seasonal Turbulence Variability on the Continental Shelf.
Creator: Lambert, Steven, Clayson, Carol Anne, Huettel, Markus, Laurent, Louis St., Weatherly, Georges, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: ABSTRACT This work presents turbulence data collected in the Gulf of Mexico in an attempt to quantify the source or sources of turbulent dissipation along the continental shelf and any possible causes for its seasonal change. In addition, this work is an effort to assist those concerned with mixing and transport problems working in similar environments. Multiple offshore research cruises were held in both the Gulf of Mexico and the Atlantic Ocean for data collection. The basis of the work is...
Show moreABSTRACT This work presents turbulence data collected in the Gulf of Mexico in an attempt to quantify the source or sources of turbulent dissipation along the continental shelf and any possible causes for its seasonal change. In addition, this work is an effort to assist those concerned with mixing and transport problems working in similar environments. Multiple offshore research cruises were held in both the Gulf of Mexico and the Atlantic Ocean for data collection. The basis of the work is a tethered profiler that measures dissipation-scale turbulence as well as temperature and conductivity at high-resolution. This data is compared against that collected by an in situ acoustic Doppler current profiler and wind meter along with salinity and conductivity measurements taken during the casts. The primary location for this study is a flat, featureless location in the northeastern portion of the Gulf known as Apalachee Bay in water of 20 meters depth. Because of the extremely gradual slope of the shelf in this region, this location is approximately 20 nautical miles off shore. Due to the tidal and wind variations in the area, along with the extreme seasonal temperature swings and surface freshwater flux, it has been found that a significant amount of turbulent energy is absorbed in this region. Density calculations indicate an abrupt seasonal overturning of the water column; cooling during the winter months creates a thermally homogeneous water column. What little stratification does exist, however, is subsequently overturned by a combination of the reversal of the along-isobath currents and increasing winds. Late summer profiles showed a well-mixed water column with very little remaining stratification.
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Date Issued: 2012
Identifier: FSU_migr_etd-4968
Format: Thesis

Title: Retroflection from Slanted Coastline Modeling Rings Injection into the South Atlantic during Glacials/Interglacials.
Creator: Zharkov, Volodymyr, Nof, Doron, Kostka, Joel, Clayson, Carol Anne, Weatherly, Georges, Program in Geophysical Fluid Dynamics, Florida State University
Abstract/Description: Recent proxies analysis suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the glacial termination. Here, we propose a mechanism through which large variations in ring production take place. To gain a preliminary understanding of...
Show moreRecent proxies analysis suggest that, at the end of the last glacial, there was a significant increase in the injection of Agulhas rings into the South Atlantic (SA). This brought about a dramatic increase in the salt-influx (from the Indian Ocean) into the SA helping re-start the then-collapsed meridional overturning cell (MOC), leading to the glacial termination. Here, we propose a mechanism through which large variations in ring production take place. To gain a preliminary understanding of the processes in question, we develop a nonlinear analytical model of retroflection from a slanted non-zonal coastline. In is known that the balance of long-shore momentum flux requires that the solution of retroflecting currents involves ring shedding on the western side. An important aspect of the ring dynamics is the ring intensity α (analogous to the Rossby number), which reaches its maximum value of unity when the upstream potential vorticity (PV) is zero. Friction leads to a slow-down and a decrease in α. The main difficulty is that the solution of the system of equations for conservation of mass and momentum of zonal currents leads to the conclusion that the ratio (Φ) of the mass flux going into the rings and the total incoming mass flux is approximately 4α/(1+2α) . This yields the "vorticity paradox"-- only relatively weak rings (α ¬ >1/2 ) could satisfy the necessary condition Φ ¬ >1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬1/2 ) could satisfy the necessary condition Φ ¬ >1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬1. Physically, this means, for example, that the momentum-flux of zero PV currents upstream is so high that, no matter how many rings are produced and no matter what size they are, they cannot compensate for it. We show here that when the slant of coastline (γ) exceeds merely 15°, Φ does not reach unity regardless of the value of α. Namely, the paradox disappears even for small slants. Our slowly varying nonlinear solution does not only let us circumvent the paradox. It also gives a detailed description of the rings growth rate and the mass flux going into the rings as a function of time. Interestingly, for significant slants (γ ¬°) , the rings reach a terminal size corresponding to a balance between the β -force and both the upstream and downstream momentum fluxes. This terminal size is unrelated to the ultimate detachment and westward drift due to β. The developed model enables us to obtain the nonlinear analytical solutions for eddy shedding, including the theoretical ranges of detached eddies radii, their propagation speeds, and their periods of detachment, as well as the average amount of mass flux going into the rings. Using the dependence of these aspects on the coastline slant, we show that there are restricted possibilities for ring detachment when the coast is oriented in the north –south direction. We define a critical coastline angle below which there is rings shedding and above which there is almost no shedding. In the case of the Agulhas region, the particular shape of the African continent implies that rings can be produced only when the retroflection occurs beyond a specific latitude where the angle is critical. During glaciation, the wind stress curl (WSC) vanished at a latitude lower than that of the critical angle, which prohibited the retroflection from producing rings. When the latitude at which the WSC vanishes migrated poleward towards its present day position, the corresponding coastline angle decreased below the critical angle and allowed for a vigorous production of rings. Simple process-oriented numerical simulations (using the Bleck and Boudra model) are in good agreement with our results and enable us to affirm that, during the glacials, the behavior of the Agulhas Current (AC) was similar to that of the modern East Australian Current (EAC), for which the coastline slant is supercritical.
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Date Issued: 2008
Identifier: FSU_migr_etd-0525
Format: Thesis

Title: A Comparison of Extreme Events in Sea Surface Temperatures Using Two Daily Satellite Datasets.
Creator: Taeger, James, Sura, Philip, Clayson, Carol Anne, Nicholson, Sharon, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study uses the high-resolution infrared radiation AVHRR (Advanced Very High Resolution Radiometer)-only and microwave radiation AMSR (Advanced Microwave Scanning Radiometer)+AVHRR sea surface temperature (SST) datasets to analyze and compare non-Gaussian statistics and extreme events for SSTs. Since the primary difference between the two datasets is the lack of AVHRR data in regions of cloud cover, higher correlations between the datasets are expected in areas of low percent daily...
Show moreThis study uses the high-resolution infrared radiation AVHRR (Advanced Very High Resolution Radiometer)-only and microwave radiation AMSR (Advanced Microwave Scanning Radiometer)+AVHRR sea surface temperature (SST) datasets to analyze and compare non-Gaussian statistics and extreme events for SSTs. Since the primary difference between the two datasets is the lack of AVHRR data in regions of cloud cover, higher correlations between the datasets are expected in areas of low percent daily-averaged total cloud cover. These are regions where both sensors usually are capable of detecting SSTs and do not rely on the process of optimum interpolation to fill missing data. Probability density functions, skewness, kurtosis, autocorrelation time scale, and standard errors are used to reveal non-Gaussianity (i.e., statistically extreme events) in the datasets, while the correlation coefficient between the datasets is used to explore extreme events beyond a certain threshold. Non-Gaussianity is present in both SST datasets, and the highest correlations of extreme events between the datasets were within positive anomalies above a certain threshold for regions of low percent daily-averaged total cloud cover.
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Date Issued: 2010
Identifier: FSU_migr_etd-1755
Format: Thesis

Title: Comparison of Wind Speed and Wind Stress in the Southern Ocean.
Creator: Chien, Chin-Ying, Speer, Kevin, Bourassa, Mark, Clayson, Carol Anne, Chanton, Jeff, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The wind speed and wind stress over the Southern Ocean (SO) is compared from the QSCAT, COAPS, ERA-Int, JRA25 and NCEP2. From the results of comparison, NCEP2 seems to poorly represent wind speed in the SO. In the summer months, the difference of wind speed and wind stress between products is small while the bias during winter is larger. Also, the difference increases in the high latitudes, close to the sea-ice zone. South of 55°S, COAPS has weaker correlation of wind stress with reanalysis...
Show moreThe wind speed and wind stress over the Southern Ocean (SO) is compared from the QSCAT, COAPS, ERA-Int, JRA25 and NCEP2. From the results of comparison, NCEP2 seems to poorly represent wind speed in the SO. In the summer months, the difference of wind speed and wind stress between products is small while the bias during winter is larger. Also, the difference increases in the high latitudes, close to the sea-ice zone. South of 55°S, COAPS has weaker correlation of wind stress with reanalysis data. The major reasons of differences between products are associated with the impact of seaice and the differences of resolution, assimilation and parameters chosen from models. From the validation by ship data, ERA-Int fits the QSCAT and ship wind speed best in the SO. The large RMS difference of Ekman pumping between products is connected to wind variance, eddy kinetic energy (EKE), especially in the South Atlantic Ocean and South Indian Ocean during fall and winter. This implies that the difference between products may result in different responses of simulated storm activities.
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Date Issued: 2009
Identifier: FSU_migr_etd-3818
Format: Thesis

Title: Resolving the Diurnal and Synoptic Variance of Scatterometer Vector Wind Observations.
Creator: Lombardi, Khara C., Bourassa, Mark, O’Brien, James, Ahlquist, Jon, Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Scatterometer observations of vector winds are used to examine the amplitudes of synoptic and diurnal cycles. Scatterometers have the advantage of providing global coverage over water; however, irregular temporal sampling complicates the analyses. A least squares technique is used in determination of the amplitudes and phases of the diurnal and synoptic cycles on spatial scales of 5°, 15°, and 30°. In open ocean areas and regions with sufficient open water, the magnitudes of the diurnal and...
Show moreScatterometer observations of vector winds are used to examine the amplitudes of synoptic and diurnal cycles. Scatterometers have the advantage of providing global coverage over water; however, irregular temporal sampling complicates the analyses. A least squares technique is used in determination of the amplitudes and phases of the diurnal and synoptic cycles on spatial scales of 5°, 15°, and 30°. In open ocean areas and regions with sufficient open water, the magnitudes of the diurnal and synoptic cycles are 1.0 ms-1 and 3.5ms-1, respectively. Diurnal amplitudes are highest in the polar regions and close to land surfaces due to sea breeze effects. The fraction of variance explained by the diurnal cycle is greatest near the equator. Synoptic amplitudes are consistently larger downwind of land from storm tracks and in the southern polar region as the time analyzed is during the southern winter season.
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Date Issued: 2004
Identifier: FSU_migr_etd-1091
Format: Thesis

Title: Atlantic Reconnaissance Vortex Message Climatology and Composites and Their Use in Characterizing Eyewall Cycles.
Creator: Piech, David J., Hart, Robert, Clayson, Carol Anne, Fuelberg, Henry, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: There has been great energy focused on tropical cyclone intensity forecasting over the past thirty years. Toward the goal of providing more accurate intensity forecasts, the role of the environment of a tropical storm has been studied at great length over the past few years while the storm itself has not. There remains considerable work left toward understanding how the tropical cyclone structure itself can be used to aid intensity forecasting. One step toward this goal for the Atlantic is by...
Show moreThere has been great energy focused on tropical cyclone intensity forecasting over the past thirty years. Toward the goal of providing more accurate intensity forecasts, the role of the environment of a tropical storm has been studied at great length over the past few years while the storm itself has not. There remains considerable work left toward understanding how the tropical cyclone structure itself can be used to aid intensity forecasting. One step toward this goal for the Atlantic is by dissecting a climatology of reconnaissance vortex message reports from the Atlantic basin between 1989 and 2005. Such an analysis will permit the comparison of tropical cyclone core structure measurements to know future intensity change. This vortex message data, which is collected from dropsondes and radar during flights into tropical disturbances, includes eye size, pressure, eye temperature, eye dewpoint, maximum flight level winds and other pertinent information. The number of occurrences for each vortex message characteristic as well as frequency plots of eye type, Julian day, latitude, longitude, temperature, dewpoint, and intensity change as a function of mean sea level pressure (MSLP) and eye size were created. The composite mean eyewall cycle was analyzed, along with the cycles of concentric eyewalls and elliptical eyewalls. Based on this vortex message climatology and analysis, an eyewall phase diagram was developed that graphically shows the evolution of a storm. These eyewall phase diagrams show how eyewall cycles evolve in time using mean MSLP, mean eye size, concentric eyewall frequency, and elliptical eyewall frequency data. Case studies include analysis of a storm undergoing an eyewall replacement cycle (Rita 2005), a rapidly weakening storm (Charley 2004), and a rapidly intensifying storm (Wilma 2005). It was discovered in this study that core storm data collected from vortex data messages could be used to confirm theories on tropical cyclone intensity. Preliminary attempts at simple forecasts comparing eye characteristics and future intensity change were done. Indeed, short-term forecasts of intensity change should utilize storm-specific structure, beginning with an analysis of that structure in intensification versus weakening events. Further work involving pattern matching trajectories and trajectory segments to forecast future storm trajectory in the eyewall phase diagram may lead to helpful analog tropical cyclone intensity forecast guidance.
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Date Issued: 2007
Identifier: FSU_migr_etd-0888
Format: Thesis

Title: Wavelets-Based Analysis of Variability in the Air-Sea Fluxes.
Creator: Brown, Jeremiah Lynn, Clayson, Carol Anne, Chicken, Eric, Bourassa, Mark, Cunningham, Phil, Program in Geophysical Fluid Dynamics, Florida State University
Abstract/Description: Presented in this research is an examination of the energy transfer between the atmosphere and the ocean via the surface energy fluxes. Typically, air-sea processes are modeled using general circulation models (GCMs) fraught with difficulties arising from numerical approximation of the theory in an attempt to align the models with global observations. As a result, GCMs are not generally able to resolve atmosphere or ocean processes to the higher resolutions required to effectively model...
Show morePresented in this research is an examination of the energy transfer between the atmosphere and the ocean via the surface energy fluxes. Typically, air-sea processes are modeled using general circulation models (GCMs) fraught with difficulties arising from numerical approximation of the theory in an attempt to align the models with global observations. As a result, GCMs are not generally able to resolve atmosphere or ocean processes to the higher resolutions required to effectively model regional phenomena. The increase in availability of regional observations has improved regional models, and subsequently caused the gap between observations and GCM model output to become a glaring problem for small scale, localized phenomena. The use of regional models, however, requires analysis tools capable of resolving signals spanning the spectrum of both large and small scale processes while preserving temporal and spatial localization of the different phenomena. Put forth herein is a wavelets-based method for analyzing the output from a high resolution air-sea model system to examine energy transfer between the atmosphere and the ocean. The model system is comprised of observed sea surface temperature data forcing the WRF-ARW atmospheric model. Energy exchange between the atmosphere and ocean is examined through the evolution of three-dimensional surface fluxes estimated by a turbulent heat flux model. Specifically, the latent and sensible heat fluxes are separated into large and small scale variability via wavelets-based windowing. The use of wavelets-based analysis is preferred because of the need to preserve spatial and temporal localization. The end result is the characterization of each heat flux in space and time, for both large and small scale variability. Heat flux variability is then related to large and small scale changes in the atmosphere and ocean.
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Date Issued: 2009
Identifier: FSU_migr_etd-2920
Format: Thesis

Title: Turbulent Dissipation in the Mid-Latitude Mixed Layer/Thermocline Transition Layer.
Creator: Rahter, Bryan, Clayson, Carol Anne, Laurent, Louis St., Dewar, William K., Froelich, Philip N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The oceanic mixed layer is a region of intense mixing, where turbulence homogenizes vertical temperature and salinity distributions down to depths of O(100) m. Below the mixed layer, in the upper layers of the stratified thermocline, turbulent energy levels are greatly reduced. The transition between these two regions is the focus of this investigation. Traditionally, this transition is assumed to take place abruptly at the mixed-layer base. However, observations suggest that enhanced...
Show moreThe oceanic mixed layer is a region of intense mixing, where turbulence homogenizes vertical temperature and salinity distributions down to depths of O(100) m. Below the mixed layer, in the upper layers of the stratified thermocline, turbulent energy levels are greatly reduced. The transition between these two regions is the focus of this investigation. Traditionally, this transition is assumed to take place abruptly at the mixed-layer base. However, observations suggest that enhanced turbulence penetrates significantly into the stratified water below the mixed layer. Here, I present an examination of existing turbulence data documenting open ocean conditions with steady wind forcing in both the sub-tropical Atlantic and Pacific. These data will allow for direct estimates of diffusivity and diapycnal flux occurring in the mixed layer/thermocline transition layer. This analysis establishes statistics for turbulence dissipation levels occurring just below the well-mixed layer, which have not been previously documented. My investigation suggests that while the transition layer thickness can vary considerably (from O(10) to O(100) m for my data), the diabatic fluxes in this region, as measured by the turbulent dissipation rate, are 4-8 times greater than in the thermocline under typical surface forcing conditions.
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Date Issued: 2010
Identifier: FSU_migr_etd-2181
Format: Thesis

Title: Quantifying the Possible Existence of Undocumented Atlantic Warm Core Cyclones in NOAA/CIRES 20th Century Reanalysis Data.
Creator: Truchelut, Ryan, Hart, Robert, Clayson, Carol Anne, Fuelberg, Henry, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The lack of satellite imagery prior to 1966 and limited aircraft reconnaissance has led to an indefinite number of tropical cyclones (TCs) in the Atlantic Basin remaining undetected by traditional surface observational networks. As a result, these cyclones were not identified by operational forecasting centers like the National Hurricane Center and are not a part of the consensus Atlantic TC climatology. While previous research suggests that this historical undersampling exists, there is...
Show moreThe lack of satellite imagery prior to 1966 and limited aircraft reconnaissance has led to an indefinite number of tropical cyclones (TCs) in the Atlantic Basin remaining undetected by traditional surface observational networks. As a result, these cyclones were not identified by operational forecasting centers like the National Hurricane Center and are not a part of the consensus Atlantic TC climatology. While previous research suggests that this historical undersampling exists, there is considerable disagreement as to its true magnitude. However, it is widely accepted that these "missing storms" have led to difficulties in interpreting long-term trends in TC activity, adding uncertainty to the dialogues over the nature, role, and existence of the Atlantic Multi-decadal Oscillation and the possible influence of climate change on TC activity, among many others. This research seeks to add information to Atlantic Basin TC climatology by developing a scheme to identify previously unknown potential cyclones in the pre-satellite era. The technique utilizes advances in global reanalysis methods to identify candidate events within certain probabilistic bounds in order to improve existing TC Best-Track reanalysis efforts. Briefly, a series of thermodynamic proxies of TC passage in the NOAA/CIRES 20th Century Reanalysis dataset is first constructed. Signatures in these metrics that are of similar amplitude and morphology to known TCs but do not correspond to known Best-Track cyclones are identified within the reanalysis solution for the test hurricane seasons of 1951 through 1958. Synoptic verification of these candidate events using historical surface observation datasets sorts the events into three broad confidence bins. The most common outcome of the observational verification process is that the candidate event does not represent a credible possible addition to BT climatology. However, a small but significant number of the candidate events were found to present highly compelling cases for further examination by ongoing TC climatology revision efforts and may eventually warrant addition to the Best-Track database. Several of these candidate events, representing a broad range of possible uses of the technique, are presented in detailed case studies. Additionally, application of the reanalysis-based methodology to the Eastern Pacific Basin demonstrates promise for use in other TC basins around the world. In general, results suggest that future work extending the technique developed in this research may potentially lead to a more complete climatological record of global TC incidence and an improved understanding of long-term trends in activity.
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Date Issued: 2011
Identifier: FSU_migr_etd-1510
Format: Thesis

Title: Wintertime ENSO Variability in Wind Direction Across the Southeast United States.
Creator: Culin, Joanne C., O'Brien, James J., Jin, Fei-Fei, Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Changes in wind direction in association with the phases of the El Niño-Southern Oscillation (ENSO) are identified over the Southeast region of the United States during the winter season (December-February). Wind roses, which depict the percentage of time the wind comes from each direction and can graphically identify the prevailing wind, are computed according to a 12-point compass for 24 stations in the region. Unfolding the wind rose into a 12-bin histogram visually demonstrates the peak...
Show moreChanges in wind direction in association with the phases of the El Niño-Southern Oscillation (ENSO) are identified over the Southeast region of the United States during the winter season (December-February). Wind roses, which depict the percentage of time the wind comes from each direction and can graphically identify the prevailing wind, are computed according to a 12-point compass for 24 stations in the region. Unfolding the wind rose into a 12-bin histogram visually demonstrates the peak frequencies in wind direction during each of the three (warm, cold and neutral) phases of ENSO. Normalized values represent the number of occurrences (counts) per month per ENSO phase, and comparison using percent changes illustrates the differences between phases. Based on similarities in wind direction characteristics, regional topography and results from a formal statistical test, stations are grouped into five geographic regions, with a representative station used to describe conditions in that region. Locations in South Florida show significant differences in the frequencies in wind direction from easterly directions during the cold phase and northerly directions during the warm phase. North Florida stations display cold phase southerly directions, and westerly and northerly directions during the warm phase, both of which are significant for much of the winter. Coastal Atlantic stations reveal winds from westerly directions for both phases. The Piedmont region demonstrates large variability in wind direction due to the influence from the Appalachian Mountains, but generally identifies warm phase and cold phase winds with more zonal influences rather than just from south or north. The Mountainous region also indicates southerly cold phase winds and northerly warm phase winds, but also reveals less of an influence from ENSO or significantly different distributions. Comparisons between observed patterns and those obtained using the NCEP/NCAR Reanalysis data reveal how the model-derived observations resolve the ENSO influence on surface wind direction at selected locations. Overall, resolution of the strength of the signals is not achieved, though the depiction of the general pattern is fair at two of the three locations. Connections between the synoptic flow and surface wind direction are examined via relationships to the storm track associated with the 250 hPa jet stream and sea level pressure patterns during each extreme ENSO phase. Discussion of reasons the NCEP reanalysis illustrates surface wind direction patterns different from those derived from observations is included.
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Date Issued: 2006
Identifier: FSU_migr_etd-2946
Format: Thesis

Title: A Recalculation of MPI Using Upper-Ocean Depth Averaged Temperatures: Climatology and Case Studies.
Creator: Watson, Michael C., Hart, Robert, Krishnamurti, T.N., Clayson, Carol Anne, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Tropical cyclone track forecasts have improved greatly in recent years. However, intensity forecasts still pose a large problem in tropical meteorology. Several theories have been developed over the past fifty years which attempt to arrive at an upper bound or Maximum Potential Intensity (MPI) of tropical cyclones. Emanuel (1988, 1995), in particular, uses the SST and atmospheric sounding to arrive at a maximum intensity (EMPI) for the hurricane using a Carnot Engine cycle approach to the...
Show moreTropical cyclone track forecasts have improved greatly in recent years. However, intensity forecasts still pose a large problem in tropical meteorology. Several theories have been developed over the past fifty years which attempt to arrive at an upper bound or Maximum Potential Intensity (MPI) of tropical cyclones. Emanuel (1988, 1995), in particular, uses the SST and atmospheric sounding to arrive at a maximum intensity (EMPI) for the hurricane using a Carnot Engine cycle approach to the energetics of the storm. While this approach has captured the upper bound or greatest intensity of hurricanes reasonably well, the use of SST for EMPI calculations may be overestimating the maximum intensity. Hurricanes draw their energy from a significant depth of the upper ocean, the average temperature of which is almost always less than the SST. Consequently, there may be more cases of tropical cyclones approaching or exceeding their EMPI than an SST-based EMPI would dictate alone. Presumably, a purely SST-based EMPI calculation would only be valid for intense storms if the entire layer affected by hurricane mixing was isothermal. Furthermore, the Carnot approach is based on an axisymmetric tropical cyclone thus ignoring potential asymmetric influences on a tropical cyclone's strength. A recalculation of the MPI climatology acknowledging this oceanic variability (NMPI) is performed here in an attempt to better isolate those storms that have approached or exceeded a more realistic MPI. Using the NODC (Levitus) World Ocean Atlas Data (1994) oceanic temperatures over five layers to a depth of 50m have been weighted to capture the upper ocean heat content, producing a climatology of mean upper ocean temperature over the globe. Having captured the upper ocean heat content a new calculation of MPI is performed. The weighting of oceanic layers chosen is supported by observations taken during the passage of Felix over the Bermuda testbed mooring on 15 August 1995 (Dickey, et al. 1998). A revised MPI climatology for the named tropical systems in the North Atlantic basin from the years 1982-2003 is produced. Results have shown that there is a dramatic impact upon the EMPI climatology when the mean upper oceanic temperature is used instead of just SST. With only the skin SST being used for EMPI, the only storms to actually exceed their MPI are recurving, poleward moving systems, a consequence of the storm accelerating rapidly and moving over cooler waters while weakening more slowly than the timescale required for the storm to come into thermodynamic balance with the decreasing SST. With the new NMPI calculation using a mean oceanic temperature, several storms in the Atlantic basin actually exceed their NMPI. Two case studies are performed. The first case study looks at Isabel (2003) and indicates the upper ocean may be a limiting factor in preventing a tropical cyclone from reaching its EMPI. The second case study examines Alex (2004) indicating that asymmetric influences, in this case trough interactions, may allow for tropical cyclones to exceed their EMPI. Further, it was discovered that hurricanes influence the atmospheric and oceanic environment such that stabilization processes from tropical cyclones may preclude development of another storm immediately after storm passage. The findings show the response time necessary for the atmosphere and the ocean to thermodynamically and synoptically readjust such that support exists for tropical cyclone formation. For the strongest storms in the Atlantic basin, it is shown that the most intense estimate of the EMPI was not found under the storm at analysis time, but rather 10-11 days before the storm actually reached the location. This shows that strong tropical cyclones begin to affect the ambient environment well before the TC center arrives at the location, and that the thermodynamic stabilization process of the environment and ocean begins a week or more prior to a strong TC's passage. It is unclear whether this stabilization is a result of the TC outflow itself, or of the modification of the intensity of the Hadley and Walker circulations in the process of TC generation and intensification.
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Date Issued: 2005
Identifier: FSU_migr_etd-7069
Format: Thesis

Title: A Study of the Viability of a Mesoscale Network Using Rooftop Weather Systems.
Creator: Hicks, Ashlee Caroline, Ruscher, Paul, Clayson, Carol Anne, Hart, Robert, Watson, Andrew I., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The need for a surface based, dense meteorological observation network in Florida has long been recognized. In 2002, scientists across the state of Florida joined together with the National Science Foundation, the REALM Project, the Florida State University, and other agencies to create the Miami-Dade Mesonet. This research is a study of the instruments used in the Miami-Dade Mesonet (the Davis Vantage Pro Weather Instruments) and of the data collected by the mesonet. The goal is to prove...
Show moreThe need for a surface based, dense meteorological observation network in Florida has long been recognized. In 2002, scientists across the state of Florida joined together with the National Science Foundation, the REALM Project, the Florida State University, and other agencies to create the Miami-Dade Mesonet. This research is a study of the instruments used in the Miami-Dade Mesonet (the Davis Vantage Pro Weather Instruments) and of the data collected by the mesonet. The goal is to prove that though the Davis Weather Instruments are inexpensive, and the placement of the instruments in the mesonet do not meet all the operational standards and procedures for surface observing, that the mesonet can still produce accurate and practical observations. This research will present an overall assessment of the accuracy and quality of the data collected. First, an internal examination of three Davis weather instruments was conducted on the roof of the James J. Love Math-Meteorology building on the FSU campus, in order to evaluate the integrity of the equipment in a controlled setting with varying parameters. Next, quality assurance procedures were run on the actual data from the Miami-Dade Mesonet to determine how well the mesonet compares with Automatic Surface Observing Systems (ASOS). Then, four case studies were conducted to examine the ability of the instruments to detect specific types of weather events, including a tornado outbreak, a record high temperature in mid-winter, a heavy rainfall event, and a sea breeze passage case. Each study evaluated a different aspect of the mesonet stations, leading to positive results proving that the systems provide operationally significant observations. The REALM Project was extended in the summer of 2005 through the Florida Panhandle and parts of central Florida, which will greatly increase observational coverage in data sparse regions in rural areas, especially in northwest Florida.
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Date Issued: 2006
Identifier: FSU_migr_etd-4062
Format: Thesis

Title: Surface Heating and Restratification of the Ocean after a Tropical Cyclone.
Creator: Deal, Robert, Clayson, Carol Anne, Hart, Robert, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Ocean transport of heat is a substantial component of the climate system but its characteristics and dynamic causes are still somewhat unknown. Prior research has shown that global observations from the ocean and atmosphere indicate that the ocean and atmosphere transport about 6 PW of energy from the equatorial regions towards the poles. Studies have shown that approximately 2 PW of that transport are carried by the ocean. It has been proposed that global tropical cyclone activity could...
Show moreOcean transport of heat is a substantial component of the climate system but its characteristics and dynamic causes are still somewhat unknown. Prior research has shown that global observations from the ocean and atmosphere indicate that the ocean and atmosphere transport about 6 PW of energy from the equatorial regions towards the poles. Studies have shown that approximately 2 PW of that transport are carried by the ocean. It has been proposed that global tropical cyclone activity could account for a large amount of the mixing needed to explain the thermohaline circulation driving this transport. However, there remain insufficient observations to conclusively prove this hypothesis. After a tropical cyclone moves across the ocean it leaves behind a wake of colder temperatures in the upper ocean. The cold wake is primarily caused by mixing, upwelling and an enthalpy flux into the atmosphere. This study makes use of the JASON-1, and TOPEX/POSEIDON satellite altimeters to investigate the amount of heating of the ocean required to re-stratify the ocean to pre storm conditions. Argo floats are also used to validate results found from the sea surface height anomalies from satellite. In order to attain the necessary spatial and temporal resolution, the Climate System Forecast Reanalysis (CFSR) model is used. Given that CFSR is a coupled atmospheric and ocean model, it enabled this study to compare the modeled storms and then the impact of storms on the ocean. After the storm passed through the area, surface heating fluxes could be determined over the duration of the storm thus providing a direct comparison of heat loss and net heat gain over the entire duration of the storm. It was found that during the time period of the cold wake, the surface heating imbalance was high enough to account for all of the rewarming of the cold wake. Therefore it is possible that global cyclone activity could account for the large amount of mixing required to explain the thermohaline circulation.
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Date Issued: 2011
Identifier: FSU_migr_etd-0060
Format: Thesis

Title: Using the Superensemble Method to Improve Eastern Pacific Tropical Cyclone Forecasting.
Creator: Jordan, Mark Rickman, Krishnamurti, T. N., Clayson, Carol Anne, Ray, Peter S., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: For many years tropical cyclone superensemble has shown remarkable skill in forecasting Atlantic tropical cyclone track and intensity. In this project tropical cyclone superensemble is applied to Eastern Pacific tropical cyclone forecasting for the 2004 Eastern Pacific tropical cyclone season. This task is completed by conducting a collection of model combination tests to discover which models perform best within the superensemble method. Then, the two main questions of this thesis are...
Show moreFor many years tropical cyclone superensemble has shown remarkable skill in forecasting Atlantic tropical cyclone track and intensity. In this project tropical cyclone superensemble is applied to Eastern Pacific tropical cyclone forecasting for the 2004 Eastern Pacific tropical cyclone season. This task is completed by conducting a collection of model combination tests to discover which models perform best within the superensemble method. Then, the two main questions of this thesis are addressed: will a combined Eastern Pacific and Atlantic training set provide superior forecasts over just using an Eastern Pacific training set, and do intensity-specific training sets provide superior forecasts over just using all storms of varying intensities? In the context of the 2004 Eastern Pacific tropical cyclone season, the answer to both questions is yes. However, the ultimate findings are quite perplexing, as an Atlantic training set provides superior forecasts when compared to forecasts using an Eastern Pacific training set or a combined-basin training set. Furthermore, forecasts made using only hurricane training usually outperform forecasts made using combined-intensity training and tropical storm training. The rest of the project uses model bias comparisons and intensity-specific error calculations to try and determine why the results are as they are.
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Date Issued: 2005
Identifier: FSU_migr_etd-3472
Format: Thesis

Title: An Intercomparison of Numerically Modeled Flux Data and Satellite-Derived Flux Data for Warm Seclusions.
Creator: Scott, Joel Paul, Bourassa, Mark A., Clayson, Carol Anne, Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Warm seclusions are large midlatitude storms that have the potential to substantially influence the turbulent heat fluxes and global energy budget. These storms have not been previously investigated from an energy and flux perspective. They have large areas of strong surface winds and rapidly moving cold fronts, which are associated with large air-sea differences of temperature and humidity. These regions contain large air-sea fluxes of latent and sensible heat. Therefore, errors in model...
Show moreWarm seclusions are large midlatitude storms that have the potential to substantially influence the turbulent heat fluxes and global energy budget. These storms have not been previously investigated from an energy and flux perspective. They have large areas of strong surface winds and rapidly moving cold fronts, which are associated with large air-sea differences of temperature and humidity. These regions contain large air-sea fluxes of latent and sensible heat. Therefore, errors in model representation of warm seclusions may introduce significant bias and uncertainty to the energy budget. The turbulent heat fluxes associated with three specific warm seclusions in different ocean basins are examined through an intercomparison of satellite- derived flux data and numerically derived flux data. The satellite data includes the SeaFlux version 0.75 data derived from SSM/I (Special Sensor Microwave/Imager), and model-derived reanalysis data includes CFSR, ERA-Interim, MERRA, and NCEP-R2 reanalysis data sets. Latent and sensible heat fluxes are computed in a physically consistent manner though the use of a bulk flux parameterization A single warm seclusion, which typically lasts between three and seven days, is responsible for approximately one quarter of the total time-integrated monthly fluxes for the ocean basin containing the warm seclusion, depending on the storm and data set under consideration. The large area of extremely large fluxes is associated with the mature phase of the cyclone. Proper representation of these fluxes is critical to determining accurate monthly- averaged, basin-wide fluxes.
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Date Issued: 2011
Identifier: FSU_migr_etd-1970
Format: Thesis

Title: Dissipation Processes in the Tongue of the Ocean.
Creator: Hooper, James A., Dewar, William, Laurent, Louis St., Clayson, Carol Anne, Kostka, Joel, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively under-studied region in terms of both its biological and physical oceanographic characteristics. This region is comprised of a deep trough along with steep boundaries that are commonly associated with elevated turbulent dissipation rates, and #949;, when impacted by currents and internal waves. A prey-field mapping cruise took place in the fall between 9/15/2008 and 10/01/2008, consisting of a series...
Show moreThe Tongue of the Ocean (TOTO) region located within the Bahamas archipelago is a relatively under-studied region in terms of both its biological and physical oceanographic characteristics. This region is comprised of a deep trough along with steep boundaries that are commonly associated with elevated turbulent dissipation rates, and #949;, when impacted by currents and internal waves. A prey-field mapping cruise took place in the fall between 9/15/2008 and 10/01/2008, consisting of a series of transects and 'clovers' to study the spatial and temporal variability. The region is characterized by a deep scattering layer (DSL), which is preyed on by nekton that serves as the food for beaked whale and other whale species. This study marks the first of its kind where concurrent measurements of acoustic backscatter and turbulence have been conducted for a nekton scattering layer well below the euphotic zone. In this novel study, turbulence data collected from a deep microstructure profiler are compared to biological and shear data collected by a 38 kHz Simrad EK 60 echosounder and a hydrographic Doppler sonar system, respectively. From these measurements, the primary processes responsible for the turbulent production in the TOTO region are assessed. The DSL around 500 m and a surface scattering layer (SSL) are investigated for raised and #949; values. Strong correlation between turbulence levels and scattering intensity of prey is generally found in the SSL with dissipation levels as large as ~10-7 W kg-1, three orders of magnitude above background levels. In the deep scattering layer, however, the correlations are relatively weak, but exhibit dissipation levels ~10-8 W kg-1. The absence of turbulence bursts of O(10-5 W kg-1) proposed to occur within dense biomass aggregations suggests biologically generated turbulence is not efficient by the marine biosphere. Areas of elevated turbulence have many implications from sustaining the abyssal stratification to transporting of nutrients and gases to and from the surface. We present an examination of the TOTO mixing levels with those from a typical open ocean site.
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Date Issued: 2011
Identifier: FSU_migr_etd-7039
Format: Thesis

Title: Characterization of Preconditioning for Ocean Deep Convection in the Sea of Japan.
Creator: Dominguez, Jorge Enrique Lopez, Clayson, Carol Anne, Chanton, Jeff, Dewar, William K., Nof, Doron, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Changes in the amount of dissolved oxygen concentration in the Sea of Japan (SOJ) over a number of years have been hypothesized to be due to the amount and depth of deep convection in this region. The first observations of the changes in oxygen concentration at depth due to deep convection in near-real time occurred during a recent Office of Naval Research-sponsored program, which included both ship tracks and floating buoy measurements. In general the process of deep convection has been...
Show moreChanges in the amount of dissolved oxygen concentration in the Sea of Japan (SOJ) over a number of years have been hypothesized to be due to the amount and depth of deep convection in this region. The first observations of the changes in oxygen concentration at depth due to deep convection in near-real time occurred during a recent Office of Naval Research-sponsored program, which included both ship tracks and floating buoy measurements. In general the process of deep convection has been divided into three general phases: preconditioning, deep convection, and lateral exchange and spreading (restratification). In this work we evaluate buoy and ship data between August of 1999 and August 2001 in order to understand the role and types of preconditioning evident in the SOJ, and compare with results from other regions with deep convection such as the Labrador Sea, the Mediterranean Sea, and the Green land Sea. Several aspects of preconditioning relative to other locations that we evaluated include the existence of a cyclonic gyre, doming of the isopycnals, and changes in mixed layer depth. The focus of our analysis was a region located south of the Peter the Great Bay and mainly north of the subpolar front (from 40.5°N to 42.5°N and from 131.0°E to 134.0° E). This has been one of the historically-designated regions of open ocean deep convection, due to its proximity to cold air outbreaks channeled through the opening in the mounts near Vladivostok. This is also the location of deep convection during the 1999 â 2001 time period from both observations and model simulations. The major findings of this study were that the surface cyclonic circulation has a primary role in preconditioning by transporting water transformed along the Siberian coast into the eastern portion of the deep convection region. We found that doming of isopycnals is not an important contributor to either preconditioning or deep convection, with a general uplifting of isopycnals of at most 100 meters. The evolution of the mixed layer properties and depth was found to be an important part of the preconditioning in SOJ. Changes in both temperature and salinity are affected by surface forcings (particularly in autumn) and by advection.
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Date Issued: 2006
Identifier: FSU_migr_etd-1058
Format: Thesis

Title: Diagnosis and Analyis of Climate Feedbacks in the NCAR CCSM3.0.
Creator: Taylor, Patrick Charles, Ellingson, Robert G., Krishnamurti, Ruby, Cai, Ming, Clayson, Carol Anne, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Climate feedbacks represent mechanisms that alter the sensitivity of the earth climate system. It has been suggested that the current spread in climate model sensitivity to a CO2 forcing is a result of different treatments of climate feedbacks. The determination of the climate system sensitivity is critical to understanding how the system will respond to a CO2 radiative forcing. The strength of a climate feedback is defined in terms of annual, global mean top of atmosphere (TOA) radiative...
Show moreClimate feedbacks represent mechanisms that alter the sensitivity of the earth climate system. It has been suggested that the current spread in climate model sensitivity to a CO2 forcing is a result of different treatments of climate feedbacks. The determination of the climate system sensitivity is critical to understanding how the system will respond to a CO2 radiative forcing. The strength of a climate feedback is defined in terms of annual, global mean top of atmosphere (TOA) radiative perturbation. However, contributions to the global, annual mean feedbacks can originate from different geographical regions and vertical layers within the atmosphere. In addition, the contributions to the annual mean TOA radiative perturbation can be disproportionately distributed throughout the annual cycle. This study performs offline, partial radiative perturbation-style, radiative calculations to determine the geographical, vertical, and seasonal distributions of the major climate feedbacks contributing to the TOA radiative energy budget: clouds, water vapor, temperature, and surface albedo. These feedback strengths are diagnosed from NCAR CCSM3.0 model output for the SRESA1B emission scenario simulated for the IPCC AR4. It is found that the tropics and sub-tropical climate responses drive the sign and strength of the water vapor and cloud feedbacks. In addition, a significant annual cycle of the SW cloud and surface albedo feedbacks is found. The inter-seasonal variations of the SW cloud and surface albedo feedbacks found here show a different pattern than previously published results. The radiative perturbations are then used as input into the newly developed Coupled Feedback Response Analysis Method (CFRAM), which uses a total energy based method to isolate partial temperature changes due to individual feedbacks in the atmosphere and at the surface. Many authors have calculated climate feedback radiative perturbations in different manners using seasonal mean, monthly mean, daily mean, and every time step model output. Monthly mean model output is used in this study. A comparison of the global mean clear sky TOA net flux calculation using monthly mean model output with the monthly mean model output TOA net flux reveals a global mean bias in the offline radiation calculations compared to the model simulated TOA net flux of +3.95 Wm-2 with a standard deviation of 3.78 Wm-2. In order to handle complexities associated with cloud overlap, the Monte Carlo Independent Column Approximation (MCICA) technique is uniquely adapted for use in the context of this study. This technique relies on a stochastic cloud generator using a maximum-random overlap rule to sample the monthly mean cloud frequency profile. It is shown that the global mean bias in the calculation of the TOA net flux compared to NCAR CCSM3.0 model output is +1.74 Wm-2 and a standard deviation of 6.71 Wm-2 using this technique. However, the results suggest that the technique provides a very good estimate of all feedback sensitivity parameters despite bias associated with using monthly mean model output.
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Date Issued: 2009
Identifier: FSU_migr_etd-1645
Format: Thesis

Title: Assessing Storm Severity Using Lightning and Radar Information.
Creator: Rudlosky, Scott D., Fuelberg, Henry E., Stallins, J. Anthony, Clayson, Carol Ann, Hart, Robert E., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Lightning data provide a valuable tool for examining interactions between multi-scale weather phenomena. Weather events are determined by complex atmospheric interactions at various spatial and temporal scales. Long-term climatologies facilitate discussion of average meteorological conditions and can help isolate the relative influence of multi-scale systems (e.g., synoptic scale, mesoscale, etc.) on local weather patterns. Lightning datasets allow the development of large-scale, long-term...
Show moreLightning data provide a valuable tool for examining interactions between multi-scale weather phenomena. Weather events are determined by complex atmospheric interactions at various spatial and temporal scales. Long-term climatologies facilitate discussion of average meteorological conditions and can help isolate the relative influence of multi-scale systems (e.g., synoptic scale, mesoscale, etc.) on local weather patterns. Lightning datasets allow the development of large-scale, long-term climatologies. These lightning climatologies then are compared with additional atmospheric observations (e.g., numerical models and radar) to examine the regional, seasonal, and storm-scale variability of thunderstorm characteristics. The National Lightning Detection Network (NLDN) underwent a major upgrade during 2002–2003 that increased its sensitivity and improved its performance. Therefore, this study applies the same methodology to pre- and post-upgrade NLDN datasets to allow direct quantitative comparisons between them and thereby examine the influence of the recent upgrade on regional distributions of cloud-to-ground (CG) lightning characteristics. Although seasonal variability must be understood to better define apparent relationships between storm properties and lightning production, seasonal differences are best described on the regional scale. Therefore, this study also examines Florida's seasonal, regional, and storm-scale CG variability during 2004–09. Since lightning data are recorded instantaneously and typically reported every minute, they also provide valuable information on storm-scale development and evolution. Automated procedures are developed to create grids of lightning and radar parameters, cluster individual storm features, and data mine the lightning and radar attributes of many individual storms. These procedures facilitate detailed analysis of relationships between lightning and radar-derived parameters in many individual storms in the Mid-Atlantic Region during 2007–09. A major goal of this research is to combine information about the near-storm environment, radar-defined storm structure, and both intra-cloud (IC) and CG lightning characteristics to better quantify relationships between storm structure, lightning production, and storm severity.
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Date Issued: 2011
Identifier: FSU_migr_etd-1929
Format: Thesis

Title: Internal Wave Propagation and Numerically Induced Diapycnal Mixing in Oceanic General Circulation Models.
Creator: Gouillon, Flavien, Chassignet, Eric, Clayson, Carol Anne, Laurent, Louis St, Morey, Steven, Huettel, Markus, O’Brien, James, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Numerical ocean models have become powerful tools for providing a realistic view of the ocean state and for describing ocean processes that are difficult to observe. Recent improvements in model performance focus on simulating realistic ocean interior mixing rates, as ocean mixing is the main physical process that creates water masses and maintains their properties. Below the mixed layer, diapycnal mixing primarily arises from the breaking of internal waves, whose energy is largely supplied...
Show moreNumerical ocean models have become powerful tools for providing a realistic view of the ocean state and for describing ocean processes that are difficult to observe. Recent improvements in model performance focus on simulating realistic ocean interior mixing rates, as ocean mixing is the main physical process that creates water masses and maintains their properties. Below the mixed layer, diapycnal mixing primarily arises from the breaking of internal waves, whose energy is largely supplied by winds and tides. This is particularly true in abyssal regions, where the barotropic tide interacts with rough topography and where high levels of diapycnal mixing have been recorded (e.g., the Hawaiian Archipelago). Many studies have discussed the representation of internal wave generation, propagation, and evolution in ocean numerical models. Expanding on these studies, this work seeks to better understand the representation of internal wave dynamics, energetics, and their associated mixing in several different classes of widely used ocean models (e.g., the HYbrid Coordinate Ocean Model, HYCOM; the Regional Ocean Modeling System, ROMS; and the MIT general circulation model, MITgcm). First, a multi-model study investigates the representation of internal waves for a wide spectrum of numerical choices, such as the horizontal and vertical resolution, the vertical coordinate, and the choice of the numerical advection scheme. Idealized configurations are compared to their corresponding analytical solutions. Some preliminary results of realistic baroclinic tidal simulations are shown for the Gulf of Mexico. Second, the spurious diapycnal mixing that exists in models with fixed vertical coordinates (i.e., geopotential and terrain following) is documented and quantified. This purely numerical error arises because, in fixed-coordinate models, the numerical framework cannot properly maintain the adiabatic properties of an advected water parcel. This unrealistic mixing of water masses can be a source of major error in both regional and global ocean models. We use the tracer flux method to compute the spurious diapycnal diffusivities for both a lockexchange scenario and a propagating internal wave field using all three models. Results for the lock exchange experiments are compared to the results of a recent study. Our results, obtained by using three different model classes, provide a comprehensive analysis of the impact of model resolution choice and numerical framework on the magnitude of the spurious diapycnal mixing and the representation of internal waves.
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Date Issued: 2010
Identifier: FSU_migr_etd-4096
Format: Thesis

Title: The Effects of Particle Loading and Temperature on Particle-Laden Buoyant Jets.
Creator: Waller, James Scott, Ruscher, Paul, Elsner, James B., Clayson, Carol Anne, Fuelberg, Henry E., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Particle-laden buoyant jets (PBJ) are free-convective flows that contain particles. Many studies have examined pure thermal plumes, discussing a symmetric self-similar structure that is common in the plume literature. Other studies have studied the fallout properties of particles embedded in plumes. Many contaminant transport models use a Gaussian, self-similar plume profile and treat particles only as a passive tracer. There is however no evidence in the literature of the simultaneous...
Show moreParticle-laden buoyant jets (PBJ) are free-convective flows that contain particles. Many studies have examined pure thermal plumes, discussing a symmetric self-similar structure that is common in the plume literature. Other studies have studied the fallout properties of particles embedded in plumes. Many contaminant transport models use a Gaussian, self-similar plume profile and treat particles only as a passive tracer. There is however no evidence in the literature of the simultaneous examination of both particle loading and temperature on the flow regimes of a PBJ. Twenty-five numerical simulations were implemented using the LANL HIGRAD numerical model, to systematically study the resulting flow regimes as the temperature and particle loading of a PBJ were systematically varied. A supplemental experiment was carried out in the laboratory, with three simulations carried out that were dynamically similar to the experiment. The comparison between experiment and simulation indicated that the model did not create turbulence as close to the domain floor as in the experiment, and further tuning is required. With awareness of this inconsistency, the twenty-five simulation results produced results of significant interest. Only two of the twenty-five simulation results produced the self-similar, Gaussian profile that is observed in the plume literature. Four of the twenty-five cases produced a no collapse PBJ scenario. The remaining cases produced either a partial collapse or full collapse of the PBJ. The use of the Grashof and buoyant Richardson numbers to characterize the flow regimes did not produce consistency with the resulting flow regime. A modified multiphase Richardson number however, accounting for particle density within a control volume, showed consistency with the resulting flow regime and indicates promise for further research and perhaps operational use. PBJ are physically relevant to a variety of particle-laden convective flows including volcanoes, industrial emissions, and contaminant transport. These results are of interest to a number of stakeholders including the DOE, DOD, DHS, and emergency management communities.
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Date Issued: 2010
Identifier: FSU_migr_etd-1329
Format: Thesis

Title: Development of a New Storm Surge Index for Global Prediction of Tropical Cyclone Generated Storm Surge.
Creator: Jordan, Mark Rickman, Clayson, Carol Anne, Georgen, Jennifer, Hart, Robert, Ruscher, Paul, Ray, Peter, Cocke, Steven, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This research involves the creation of a new storm surge index that incorporates many variables important in storm surge generation like maximum winds, radius of maximum winds, pressure, translation speed, and bathymetry. Using a two-dimensional, barotropic ocean model, power laws have been developed that describe the relationship between storm surge and changes in maximum wind, radius of maximum winds, pressure, and bathymetry. Direct curve fitting is used to describe the relationship...
Show moreThis research involves the creation of a new storm surge index that incorporates many variables important in storm surge generation like maximum winds, radius of maximum winds, pressure, translation speed, and bathymetry. Using a two-dimensional, barotropic ocean model, power laws have been developed that describe the relationship between storm surge and changes in maximum wind, radius of maximum winds, pressure, and bathymetry. Direct curve fitting is used to describe the relationship between storm surge and changes in translation speed since a power-law relationship does not exist in that case. A database of 39 landfalling, United States hurricanes between 1986 and 2007 is used to evaluate the quality of the index. Storm parameters for all database storms are compiled using the extended best track dataset, and an index value is calculated for each storm in the database. Correlation analysis is then performed using the index values and observed maximum storm surge heights. Finally, an extensive error analysis is presented to demonstrate uncertainties in the index in both forecast and post-analysis situations.
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Date Issued: 2008
Identifier: FSU_migr_etd-3473
Format: Thesis

Title: Deep Circulation in the Eastern South Pacific Ocean.
Creator: Faure, Vincent, Speer, Kevin, Clayson, Carol Anne, Nof, Doron, Weatherly, Georges, Landing, William, Froelich, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: It has been suggested in older and recent literature that a broad deep eastern boundary flow is linking the equatorial Pacific Ocean to the Southern Ocean. The depth range of this flow corresponds to the Pacific Deep Water (2500m) where it is suggested by the distribution of primordial 3He originating from the East Pacific Rise. In this study, we propose to use a large set of data along with inverse techniques to estimate the stationary advection and diffusion of water properties and tracer...
Show moreIt has been suggested in older and recent literature that a broad deep eastern boundary flow is linking the equatorial Pacific Ocean to the Southern Ocean. The depth range of this flow corresponds to the Pacific Deep Water (2500m) where it is suggested by the distribution of primordial 3He originating from the East Pacific Rise. In this study, we propose to use a large set of data along with inverse techniques to estimate the stationary advection and diffusion of water properties and tracer concentrations (potential vorticity, potential temperature, salinity, dissolved oxygen and silica concentration) in the area of interest. The various data are combined into an new inverse model first developed by McKeague et al. (2005), Herbei et al. (2006). The model uses a forward advection-diffusion model and Markov Chain Monte-Carlo techniques to give estimates of velocities along and across surfaces of neutral density as well as isopycnal diffusivities. It is composed of 9 layers between the 27.4 and 28 neutral densities. The circulation in the upper layers of the model compares well with direct independent estimates of velocities from subsurface float trajectories (WOCE and Argo). We investigate the water exchange in the deeper layers in regards to the 3He distribution along the Eastern boundary and its mixing with the Antarctic Circumpolar Current. The model is able to estimate vertically dependent rates of oxygen utilization as well as lateral eddy diffusivities of tracers.
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Date Issued: 2009
Identifier: FSU_migr_etd-4490
Format: Thesis

Title: Wildfire Dynamics: Understanding Some Behavior Trends.
Creator: Canfield, Jesse M., Nof, Doron, Hart, Robert, Speer, Kevin, Ewald, Brian, Clarke, Allan, Krishnamurti, Ruby, Linn, Rodman, Clayson, Carol Anne, Program in Geophysical Fluid Dynamics, Florida State University
Abstract/Description: This dissertation explores wildfire dynamics. Chapters 2 and 3 are peer reviewed journal articles that present an understanding of three-dimensionality in grass fires and how it affects forward rate of spread (ROS) of the fire. In Chapter 2 the numerical model HIGRAD/FIRETEC was used to give arguments supporting that modeling wildfire in a two-dimensional vertical and stream-wise plane does not represent all of the physics that are required to determine a meaningful forward ROS. Chapter 2...
Show moreThis dissertation explores wildfire dynamics. Chapters 2 and 3 are peer reviewed journal articles that present an understanding of three-dimensionality in grass fires and how it affects forward rate of spread (ROS) of the fire. In Chapter 2 the numerical model HIGRAD/FIRETEC was used to give arguments supporting that modeling wildfire in a two-dimensional vertical and stream-wise plane does not represent all of the physics that are required to determine a meaningful forward ROS. Chapter 2 inspired the work that makes up chapter 3. In chapter 3, HIGRAD/FIRETEC was again used, to determine the effect that ignition line length has on forward ROS. In both chapters, finger shaped structures were present in the combusting fuels, upstream of the fire front. The fingers correlated with counter-rotating vortex pairs in the gas-phase above them. It was also shown that increasing ignition line length does indeed increase forward ROS, an expected result supported by previous investigations. Results were presented that suggest physical reasons why a spreading grass fire develops flanks that move forward slower than the front of the fire. Chapter 4 describes the gas phase in the planetary boundary layer (PBL), where fires and other phenomena occur. A muti-component gas phase model was derived that represents individual ideal gas species. The mass dependent nature of this model allows the individual species to have dynamic effects on the flow field. The multi-component model was then coupled to HIGRAD to explore three PBL scenarios. The purpose of the first case was to numerically spin-up a moist unstable PBL. The second case used the mixture model to look at a hypothetical scenario representative of the Las Conchas wildfire. In the second case, an idealized column of a gaseous mixture containing heat, dry air, water vapor, and fullerene was initialized over the topography where the Las Conchas fire occurred. The gas column represented an idealized fire plume. As predicted, the column collapsed under its own weight. However, parts of the column rose to higher elevations too. The third case was to use the results from the first case to model fugitive methane in an unstable PBL. In this case, a small amount of methane was fluxed into a grid cell on the bottom boundary of the spun-up, moist PBL from the first case. The evolution of the methane plume was and continues to be studied. Some preliminary results are presented where methane concentration is compared to data collected from a field experiment. Chapter 5 is the conclusion. In this chapter, the results from chapters 2, 3, and 4 are summarized. An analytical fire spread model is proposed that ties chapters 2 and 3 to chapter 4. This spread model is a two-layer, multi-phase set of governing equations. It is assumed that the gas phase is a thin layer relative to the horizontal. This thin layer contains laminar, diffusion flames. The vertical distance that the flames remain laminar and diffusive determines the thickness of the layer. In other words, the vertical distance from the ground to the transition point to turbulent flames, determines the thickness of the layer.
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Date Issued: 2014
Identifier: FSU_migr_etd-8749
Format: Thesis

Title: Warm Season Mesoscale Superensemble Precipitation Forecasts.
Creator: Cartwright, Tina J., Krishnamurti, T. N., Krishnamurti, Ruby, Ruscher, Paul H., Clayson, Carol Anne, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: With current computational limitations, the accuracy of high resolution precipitation forecasts has limited temporal and spatial resolutions. Forecast accuracy drops dramatically after a 24 hour forecast. Current operational mesoscale models run only to 48-72 hours. However, with the recent development of the superensemble technique, the potential to improve precipitation forecasts at the regional resolution exists. The purpose of this study is to apply the superensemble technique to regional...
Show moreWith current computational limitations, the accuracy of high resolution precipitation forecasts has limited temporal and spatial resolutions. Forecast accuracy drops dramatically after a 24 hour forecast. Current operational mesoscale models run only to 48-72 hours. However, with the recent development of the superensemble technique, the potential to improve precipitation forecasts at the regional resolution exists. The purpose of this study is to apply the superensemble technique to regional precipitation forecasts to generate more accurate forecasts pinpointing exact locations and intensities of strong precipitation systems. This study will determine the skill and predictability of a regional superensemble forecast out to 60 hours. Precipitation results were stratified by time of day to allow detections of the diurnal cycle. As expected, warm season daytime precipitation is commonly forced by convection which is difficult to accurately model. Results were also stratified by lead time which reveals how quickly the forecasts degrade in time. Currently, mesoscale models such as those utilized in the ensemble are approaching the limits of precipitation predictability. Major synoptic regimes, including subtropical high, mid-latitude trough/front, and tropical cyclone, were examined to determine the skill of the superensemble under various synoptic conditions. Finally, different rainfall intensities were examined which revealed the superensemble forecast significantly improved the forecast at significant rainfall amounts. The regional superensemble consists of 12 to 60-hour daily quantitative precipitation forecasts from 6 models. Five are independent operational models, and one comes from the physical-initialized FSU regional spectral model. The superensemble forecasts are verified during the summer 2003 season over the southeastern US using a merged RFC Stage IV radar/gauge and satellite analyses. Precipitation forecasts were skillful in outperforming the operational models at all model times. Skill measurements that were examined include ETS, Bias, FAR, and POD.
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Date Issued: 2004
Identifier: FSU_migr_etd-4141
Format: Thesis

Title: The Use of Scale Interactions as a Framework for the Maintenance of the Madden Julian Oscillation.
Creator: O'Shay, Adam J., Krishnamurti, T. N., Krishamurti, Ruby, Clayson, Carol Anne, Hart, Robert, O'Brien, James J., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: In this study, a scale interactions and energetics formulation is utilized to examine the kinetic (KE) and available potential energy (APE) maintenance of the Madden Julian Oscillation (MJO). An analysis that computes the energy exchange among frequencies of atmospheric phenomena, with the MJO as the centerpiece, is the primary focus of this study. The rotational and divergent components of the wind have been examined here, as these components have been found to elicit significant information...
Show moreIn this study, a scale interactions and energetics formulation is utilized to examine the kinetic (KE) and available potential energy (APE) maintenance of the Madden Julian Oscillation (MJO). An analysis that computes the energy exchange among frequencies of atmospheric phenomena, with the MJO as the centerpiece, is the primary focus of this study. The rotational and divergent components of the wind have been examined here, as these components have been found to elicit significant information regarding the overall atmospheric circulation, globally, in the tropics and in both hemispheric middle-latitude regions. The interactions among frequencies can occur both in-scale (quasi-nonlinear quadratic) and between scales (nonlinear triad interactions). A third examined component of the energy equations is the APE to KE, baroclinic exchange over specified frequencies. This is also of the in-scale type of exchanges. An analysis of 22 years of global, full-atmosphere (ECMWF) Re-Analysis data is undertaken, where the energetics of the MJO are computed for the global, tropics and hemispheric middle-latitudes. Specified frequencies with the time period of 3-7 days (synoptic), 30-60 days (MJO), 180 days (Semi-Annual), 365 days (Annual), 3-7 years (El Nino) and decadal (10 years and beyond) were the primary indices of MJO maintenance used within this study. These energetics were computed for the 300 hPa and 850 hPa levels of the atmosphere, for the entire 22 years, the 30 hPa maximum amplitude region of the Quasi-Biennial Oscillation, and for selected time periods during the ENSO episode lasting from 1997 to early 2001. The salient findings of this research are that the MJO is maintained within the upper and lower troposphere primarily by the baroclinic conversion of APE to KE through in-scale exchanges. The MJO is secondarily perpetuated, by the nonlinear scale interactions occurring among a triad of scales, that act to contribute positively to the MJO time-scale. Finally, the time mean-time transient buildup of KE on the MJO time-scale ranks third in the overall maintenance of the MJO. In the context of the KE exchanges, the rotational components have been illustrated to dominate those of the divergent form, which agrees with previous research indicating that the rotational component of the wind accounts for nearly 95 percent of the total horizontal wind. For the APE exchanges, the converse to the KE exchanges has been found, where the divergent components of the transfers typically is the prominent component among it and the rotational component. This is explained to occur as the divergent component of the wind typically has a stronger meridional component than the rotational wind, thus an increase in the horizontal temperature advection that comprises the APE equations is larger for the divergent component. Results in this study indicate that at 30 hPa, the QBO does not transfer KE to the MJO time-scale via triad interactions. Among the ENSO energetics computations, the maintenance of the MJO within the tropics during the neutral phase is dominated by the high frequency rotational component, whereas in the El Nino phase, the weak MJOs are losing energy most prominently in the tropics through the semi-annual time-scale. This result indicates that the nonlinear interactions of a triad of scales can offer one scale as the primary contributor of the MJO maintenance, while in a weak MJO phase, another unique scale can be leading the removal of KE from the MJO. For the ENSO event, geographic distributions of the triad exchanges of KE and APE components displayed strong positive contributions in latitudes poleward of 10 degrees, largely due to the stronger wind-speeds in these regions advecting the vorticity (rotational) and divergence (divergent) at comparatively larger magnitudes. The geographic distributions of KE and APE also made clear the strong spatial variability occurring among all time-scales.
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Date Issued: 2005
Identifier: FSU_migr_etd-2450
Format: Thesis

Title: The Development of a High-Resolution Coupled Atmosphere-Ocean Model and Applications Toward Understanding the Limiting Factors for Tropical Cyclone Intensity Prediction.
Creator: Winterbottom, Henry R., Chassignet, Eric P., Clayson, Carol Anne, Dewar, William K., Hart, Robert E., Ruscher, Paul H., Bourassa, Mark A., Powell, Mark D., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The prediction of tropical cyclone (TC) motion has improved greatly in recent decades. However, similar trends remain absent with respect to TC intensity prediction. Several hypotheses have been proposed attempting to explain why dynamical NWP models struggle to predict TC intensity. The leading candidates are as follows: (1) the lack of an evolving ocean (i.e., sea-surface temperature) boundary condition which responds as a function of the atmosphere (e.g., TC) forcing, (2) inappropriate...
Show moreThe prediction of tropical cyclone (TC) motion has improved greatly in recent decades. However, similar trends remain absent with respect to TC intensity prediction. Several hypotheses have been proposed attempting to explain why dynamical NWP models struggle to predict TC intensity. The leading candidates are as follows: (1) the lack of an evolving ocean (i.e., sea-surface temperature) boundary condition which responds as a function of the atmosphere (e.g., TC) forcing, (2) inappropriate initial conditions for the TC vortex (e.g., lack of data assimilation methods), (3) NWP model grid-length resolutions which are unable to resolve the temporal and length scale for the features believed responsible for TC vortex intensity. modulations (i.e., eye-wall dynamics, momentum transport, vortex Rossby wave interactions, etc.), and (4) physical parametrization which do not adequately represent the air-sea interactions observed during TC passage. In this study, a coupling algorithm for two independent, high-resolution, and state-of-the-art atmosphere and ocean models is developed. The atmosphere model -- the Advanced Weather Research and Forecasting (WRF-ARW) model is coupled to the HYbrid Coordinate Ocean Model (HYCOM) using a (UNIX) platform independent and innovative coupling methodology. Further, within the WRF-ARW framework, a dynamic initialization algorithm is developed to specify the TC vortex initial condition while preserving the synoptic-scale environment. Each of the tools developed in this study is implemented for a selected case-study: TC Bertha (2008) and TC Gustav (2008) for the coupled-model and TC vortex initialization, respectively. The experiment results suggest that the successful prediction (with respect to the observations) for both the ocean response and the TC intensity cannot be achieved by simply incorporating (i.e., coupling) an ocean model and/or by improving the initial structure for the TC. Rather the physical parametrization governing the air-sea interactions is suggested as the one of the weaknesses for the NWP model. This hypothesis is (indirectly) supported through a diagnostic evaluation of the synoptic-scale features (e.g., sea-level pressure and the deep-layer mean wind beyond the influence of the TC) while the assimilated TC vortex is nudged toward the observed intensity value. It is found -- in the case of TC Gustav (2008) using WRF-ARW, that as the assimilated TC vortex intensity approaches that of the observed, the balance between the mass and momentum states for WRF-ARW is compromised leading to unrealistic features for the environmental sea-level pressure and deep-layer (800- to 200-hPa) mean wind surrounding the TC. Forcing WRF-ARW to assimilate a TC vortex of the observed maximum wind-speed intensity may ultimately compromise the prediction for the TC's motion and subsequently mitigate any gains for the corresponding intensity prediction.Suggestions for additions to the coupled atmosphere-ocean model include a wave-model (WAVEWATCH3), the assimilation of troposphere thermodynamic observations, and modifications to the existing atmospheric boundary-layer parametrization. The current suite of atmosphere model parametrizations do not accurately simulate the observed azimuthal and radial variations for the exchange coefficients (e.g., drag and enthalpy) that have been indicated as potentialpredictor variables for TC intensity modulation. However, these modifications should be implemented only after the limitations for the current coupled-model and TC vortex initialization methods are fully evaluated.
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Date Issued: 2010
Identifier: FSU_migr_etd-0928
Format: Thesis

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