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Title: Dynamics of the Wind Field Expansion Associated with Extratropically Transitioning Tropical Cyclones.
Creator: Evans, Allen Clark, Hart, Robert, Cunningham, Philip, Krishnamurti, T. N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Extratropical transition, or ET, can be characterized by the transformation of an initially symmetric, warm-core tropical cyclone into an initially cold-core, asymmetric extratropical cyclone. As a consequence of undergoing transition, changes in the synoptic and dynamic characteristics of the cyclone are realized. Of particular note is the wind field evolution, one of the aspects of ET that has seen little research into its causes. Previous informal theories toward understanding the wind...
Show moreExtratropical transition, or ET, can be characterized by the transformation of an initially symmetric, warm-core tropical cyclone into an initially cold-core, asymmetric extratropical cyclone. As a consequence of undergoing transition, changes in the synoptic and dynamic characteristics of the cyclone are realized. Of particular note is the wind field evolution, one of the aspects of ET that has seen little research into its causes. Previous informal theories toward understanding the wind field evolution based upon key meteorological conservation principles do not accurately account for its observed evolution, while formal studies into other aspects of the ET process (e.g. Ritchie et al. 2001, Jones et al. 2003) have only mentioned its existence or its resultant impacts. This study attempts to bridge this gap by analyzing the physical and dynamical mechanisms involved with both the expansion of the wind field and outward movement of the radial wind maximum during the transition process. One ET case, North Atlantic Tropical Cyclone Bonnie (1998), is modeled using the Pennsylvania State University/NCAR Mesoscale Model version 5 (MM5; Dudhia 1993) at 12km horizontal resolution. The evolution of the cyclone within the model output is found to be an accurate measure of reality when compared to the observed track and dynamical evolution of the cyclone. Analysis of the model output shows that the expansion of the wind field is brought about by the net import of absolute angular momentum from a midlatitude trough of low pressure along descending isentropic trajectories in the western semicircle of the cyclone. Export of absolute angular momentum in the outward branch of the secondary circulation in the eastern semicircle of the cyclone partially negates but does not balance the import to the west; thus a net import of momentum into the cyclone is seen. Redistribution of momentum within the cyclone is accomplished through vertical pressure torques. The overall evolution is found to be consistent with that for a developing extratropical cyclone as shown by Johnson and Downey (1976). Net cooling (warming) inside (outside) of the radial wind maximum is shown to lead to the outward movement of this feature via a hydrostatic response in the radial height gradient, a response opposite to that seen with eyewall contraction (Shapiro and Willoughby 1982) yet consistent with the transition into a cold-core vortex. The observed results are used to formulate a conceptual model for the evolution of the wind field during ET. Implications toward the wind field evolution with other post-ET structural evolutions, such as warm seclusion cyclones and those that remain cold core yet strengthen (e.g. Hart et al. 2006), are drawn in conjunction with the observed results. Related concepts of vertical wind shear and cyclone size are discussed as natural outgrowths of the wind field expansion process.
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Date Issued: 2006
Identifier: FSU_migr_etd-0439
Format: Thesis

Title: The Thermodynamic Evolution of Recurving Tropical Cyclone Bonnie (1998).
Creator: Evans, Allen Clark, Hart, Robert E., Elsner, James B., Krishnamurti, T. N., Reasor, Paul, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State...
Show moreEvans, Allen Clark, Hart, Robert E., Elsner, James B., Krishnamurti, T. N., Reasor, Paul, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: One of the defining characteristics of the extratropical transition of tropical cyclones is the transition of the warm core thermal structure associated with the tropical cyclone into an initially cold core thermal structure associated with the extratropical cyclone. Despite this being a defining characteristic of the extratropical transition process, the literature expresses no consensus agreement upon or a quantification and physical description of the factors that explicitly cause this...
Show moreOne of the defining characteristics of the extratropical transition of tropical cyclones is the transition of the warm core thermal structure associated with the tropical cyclone into an initially cold core thermal structure associated with the extratropical cyclone. Despite this being a defining characteristic of the extratropical transition process, the literature expresses no consensus agreement upon or a quantification and physical description of the factors that explicitly cause this transition to occur. Understanding this evolution is important in order to better forecast and describe the evolution of physical features within the cyclone such as its four-dimensional wind field structure and to begin to quantify the contributors to the poleward transport of heat energy associated with the transitioning cyclone and its impacts upon hemisphere weather patterns and model predictability. This work employs a suite of high resolution numerical simulations in order to quantify and physically describe the evolution of the thermodynamic structure associated with a typical extratropical transition case, North Atlantic Tropical Cyclone Bonnie of 1998. Thermodynamic budgets native to the numerical model's primitive equation set and physical parameterizations are computed during the transition phase of the cyclone within a four-dimensional analysis framework. The observed warm-to-cold thermal profile evolution is found to arise out of an imbalance between dynamical cooling and parameterized warming contributions. This dynamical cooling, as influenced by horizontal advection, vertical advection and adiabatic cooling, and total divergence, is of greater magnitude than warming associated with latent heat release due to condensation and deposition processes within the transitioning cyclone's delta rain region. While the net thermodynamic evolution is found to be relatively resolution-insensitive, specific details of the thermodynamic balance are found to vary depending upon the horizontal resolution of the given numerical simulation. The thermodynamic evolution is ultimately shown to be a natural outgrowth of the factors that influence extratropical transition as a whole and is found to closely resemble the mature and occluding stages of purely cold-core extratropical cyclone development.
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Date Issued: 2009
Identifier: FSU_migr_etd-0440
Format: Thesis

Title: Microwave Radiative Transfer Modeling of Ice in the Atmosphere: A Critical Examination of Cloud Ice Utilizing Remote Sensing.
Creator: Zuiderweg, Adriaan T., Liu, Guosheng, Ruscher, Paul, Kim, KwangYul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Tropospheric cloud ice has a significant impact on the earth's radiative balance and climate, and to help improve the ability to forecast short-term through climatological-scale weather, the importance of quantification of these ice particles is not to be underestimated. To that end, the study presented here describes an attempt to accomplish large spatial-scale integrated ice water quantity (known as ice water path) retrieval via remote sensing in the microwave band (80-300GHz), where...
Show moreTropospheric cloud ice has a significant impact on the earth's radiative balance and climate, and to help improve the ability to forecast short-term through climatological-scale weather, the importance of quantification of these ice particles is not to be underestimated. To that end, the study presented here describes an attempt to accomplish large spatial-scale integrated ice water quantity (known as ice water path) retrieval via remote sensing in the microwave band (80-300GHz), where effects from ice crystals become detectable via scattering of terrestrial radiation. At the heart of this study is the use of a radiative transfer model in conjunction with data from surface-based instrumentation to simulate atmospheric brightness temperatures at microwave frequencies, and to compare the simulated results to observational data from the Advanced Microwave Sounding Unit - B instrument on the NOAA-15 polar orbiting platform. However, this cannot be done without first discussing the nature of ice crystals in the atmosphere and the scattering modes that result from their interaction with energy, and the implementation of approximations thereof for model usage. Case studies are performed using the model to establish the sensitivity and behavior of the model under differing conditions, and these are compared to real-world data. Subsequently ice water path retrieval from satellite data utilizing Bayesian theory is attempted, with somewhat limited success, and the results hereof are discussed. Finally, known error sources are examined with possibilities for improvement, and ideas for future work in the field presented.
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Date Issued: 2006
Identifier: FSU_migr_etd-0476
Format: Thesis

Title: Spatiotemporal Variability and Prediction of Rainfall over the Eastern Caribbean.
Creator: Pologne, Lawrence, Cai, Ming, Krishnamurti, T. N., Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Recent, recurrent, and extreme weather events have been a cause for concern over the Eastern Caribbean (EC). Given the dependence on rainfall of agriculture, the main stay of the fragile economies throughout the region, accurate and timely forecasts of seasonal rainfall need to be issued to facilitate decision making in Water Resource Management. Understanding the causes of climate variability can lead to the development of more robust models for climate prediction. So as a diagnostic...
Show moreRecent, recurrent, and extreme weather events have been a cause for concern over the Eastern Caribbean (EC). Given the dependence on rainfall of agriculture, the main stay of the fragile economies throughout the region, accurate and timely forecasts of seasonal rainfall need to be issued to facilitate decision making in Water Resource Management. Understanding the causes of climate variability can lead to the development of more robust models for climate prediction. So as a diagnostic approach, different techniques are employed. Empirical Orthogonal Function (EOF) analysis is performed in order to isolate the different modes of rainfall variability as well as investigating their amplitudinal modulations. The evolution of external forcing mechanisms that impact on precipitation extremes is also investigated with the use of composites. Based on the strength of the relationship between Sea Surface Temperature Anomalies (SSTA) and EC rainfall, a statistical model is subsequently developed using multivariate Canonical Correlation Analysis (CCA) to predict rainfall over the region on seasonal time scales. The CCA model demonstrated useful skill in predicting seasonal rainfall over the EC up to six months lead. The highest average predictive skill is realized for the June-July-August (JJA) season at one-month lead, while the lowest average skill is realized for the March-April-May (MAM) season at five months lead. The December-January-February (DJF) season maintained steady skill throughout six months lead. Below normal conditions are forecasted by the CCA model for the 2004/2005 dry season (DJF/2004-05, MAM/2005). This outlook is in part, verified from seasonal rainfall totals at two stations within the EC. The outlook for the coming rainy season is for above normal conditions.
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Date Issued: 2005
Identifier: FSU_migr_etd-0510
Format: Thesis

Title: Assessment of Groundwater Discharge to Lake Barco via Radon Tracing.
Creator: Stringer, Christina Elaine, Burnett, William C., Chanton, Jeffrey P., Sturges, Wilton, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Groundwater-surface water interactions in lakes have been gaining attention in recent years as scientists have recognized the potential significance that groundwater has as a source of nutrients and contaminants to aquatic ecosystems. Such interactions need to be understood in order for us to protect important ecosystems and quantify nutrient loading into lakes. This project set out to test the idea that good estimates could be made of groundwater inputs into Florida lakes using a simple...
Show moreGroundwater-surface water interactions in lakes have been gaining attention in recent years as scientists have recognized the potential significance that groundwater has as a source of nutrients and contaminants to aquatic ecosystems. Such interactions need to be understood in order for us to protect important ecosystems and quantify nutrient loading into lakes. This project set out to test the idea that good estimates could be made of groundwater inputs into Florida lakes using a simple geochemical tracer technique. We hypothesize that a relatively small number of measurements would be sufficient to provide a reasonably good (a factor of 2) estimate of groundwater discharge. Naturally occurring 222Rn makes an ideal tracer because it exists in enriched concentrations in groundwater relative to surface water. We used Lake Barco, a small seepage lake in the Katherine Ordway Preserve, for a detailed pilot study in order to test this hypothesis. The preserve is located about 34 km east of Gainesville, Florida and makes an excellent research site because it is maintained in a pristine state as it is closed off to public access. Two intensive samplings were completed, one in the "dry" season (March 2002) and one in the "wet" season (August 2003). In addition, periodic sampling trips were made to the lake every few weeks to evaluate the spatial and temporal patterns of radon distribution. A 222Rn mass balance was constructed for the lake to evaluate radon fluxes. Once the 222Rn fluxes were determined, groundwater inputs were estimated by dividing these fluxes by the concentration of radon in the water seeping into the lake. The radon concentration is estimated by sediment equilibration experiments using grab samples of sediment and radon activity measurements from monitor wells. We also constructed a traditional hydrologic water budget for Lake Barco. All hydrological variables were either measured or estimated and substituted into a water balance equation, which was then solved for the net groundwater flow term. These estimates were then compared to those from the 222Rn model. Our 222Rn measurements show little discernible spatial variation of radon inventories in the lake on any given day of sampling. Inventories measured at five different stations during the two different intensive sampling trips were all within ±13% of the mean value for each sampling. This amount of variation is considered insignificant, as the estimated analytical variation for the radon measurements is ±10%. We also found that we can estimate the lake inventory at any one station by collecting triplicate samples approximately one meter over the bottom at a single central sampling station. However, our results did display significant temporal variability, responding to rainfall trends that can influence the recharge rates. So, in a lake the size of Lake Barco (12 ha), reasonable groundwater discharge estimates at any given time can be made by triplicate analysis of radon in near-bottom waters and collection and processing of a few sediment samples. The estimations of groundwater discharge to the lake over the period of our study were, on average, 13,000 m3/month and 18,000 m3/month for the radon model and hydrologic budget, respectively. The water balance based estimate might be somewhat low due to differences in hydrogeologic movement under such dry conditions or the large error associated with budget estimations. Considering the large uncertainties in estimating groundwater flow via a hydrologic budget, agreement within a factor of two is considered satisfactory.
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Date Issued: 2004
Identifier: FSU_migr_etd-0395
Format: Thesis

Title: Modeling Streamflow Using Gauge-Only versus Multi-Sensor Rainfall.
Creator: Sullivan, John Lawrence, Fuelberg, Henry E., Ruscher, Paul H., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study evaluates the impacts of two types of rainfall input on simulated streamflow using a specialized, fully-distributed hydrologic model—the Watershed Assessment Model (WAM). We compare gauge-only Thiessen polygon input data with the gridded 4 × 4 km Florida State University (FSU) version of the National Weather Service (NWS) Multi-sensor Precipitation Estimator (MPE) scheme. Streamflow results are compared to observed amounts over a six year period (2000-2005) at two U.S. Geological...
Show moreThis study evaluates the impacts of two types of rainfall input on simulated streamflow using a specialized, fully-distributed hydrologic model—the Watershed Assessment Model (WAM). We compare gauge-only Thiessen polygon input data with the gridded 4 × 4 km Florida State University (FSU) version of the National Weather Service (NWS) Multi-sensor Precipitation Estimator (MPE) scheme. Streamflow results are compared to observed amounts over a six year period (2000-2005) at two U.S. Geological Survey (USGS) stream gauge sites in the greater Florida Suwannee River basin. One catchment has an area of 1505 km2, while the smaller catchment is 500 km2. Previous comparisons have been made between the two different precipitation data types using mean areal precipitation calculations over several Florida basins. This study of streamflow expands on those findings. Results show significant differences in simulated streamflow when the higher-resolution FSU MPE rainfall data are input to WAM. However, the FSU MPE dataset does not always provide better results with this model configuration. The improvements in WAM simulated streamflow depend on a combination of factors, including the desired type of comparison with observed amounts (volume or correlation), rainfall pattern characteristics, and individual event scenarios. The accumulations of FSU MPE WAM streamflow generally are found to be more accurate than those from Thiessen polygons. During drought periods, MPE-derived streamflow provided more accurate accumulations, but coefficients of determination were not always improved. During years with more average rainfall events, FSU MPE produced greater underestimates of accumulation amounts, and thus a better approximation by the Thiessen polygon input. Seasonal results emphasized the weaknesses of each data source. Rain gauges usually are not able to capture the small scale spatial variability of summer rainfall events. And, radar-derived precipitation generally is underestimated during relatively low top stratiform winter events. When simulating streamflow with a hydrologic model using rain gauge input, it is apparent that gauge locations are very important. Generally speaking, increasing the spatial density of gauges will produce a better representation of rainfall. Our small basin was found to be prone to significant underestimates of accumulations and lower coefficients of determination regardless of the rainfall input. However, statistical differences between our larger and smaller basins are not as dramatic with the FSU MPE data. Current results are based on the WAM model as configured for this study. Results from other models and/or other configurations may be different. Although there appear to be errors in both WAM's ability to utilize the rainfall data properly and in the rainfall data measurements themselves, the results highlight areas where both can be improved.
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Date Issued: 2008
Identifier: FSU_migr_etd-0403
Format: Thesis

Title: Metabolic Pathways in Natural Systems: A Tracer Study of Carbon Isotopes.
Creator: Prater, James L., Chanton, Jeffrey P., Wang, Yang, Kostka, Joel E., Mortazavi, Behzad, Burnett, William C., Winchester, John W., Department of Earth, Ocean and Atmospheric...
Show morePrater, James L., Chanton, Jeffrey P., Wang, Yang, Kostka, Joel E., Mortazavi, Behzad, Burnett, William C., Winchester, John W., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: The δ13C value of foliage respiration has been considered a constant in the past and modeling efforts have assumed that the δ13C value of foliage respiration is constant and is directly related to substrate without any fractionation. Consecutive δ13C measurements of foliage dark-respired CO2 (δ13Cr) for slash pine trees (Pinus elliottii) over several diel cycles were used to test the hypothesis that significant variation in δ13Cr would be observed. δ13Cr values collected in daylight from all...
Show moreThe δ13C value of foliage respiration has been considered a constant in the past and modeling efforts have assumed that the δ13C value of foliage respiration is constant and is directly related to substrate without any fractionation. Consecutive δ13C measurements of foliage dark-respired CO2 (δ13Cr) for slash pine trees (Pinus elliottii) over several diel cycles were used to test the hypothesis that significant variation in δ13Cr would be observed. δ13Cr values collected in daylight from all time series showed mid- day 13C enrichment (5 – 10‰) relative to bulk biomass, but values become more 13C depleted following shading and at night and approach bulk-biomass δ13C values by dawn. Assimilation model results suggest that respiration during daylight has the potential to significantly affect ∆13C by as much as 1.6‰, but night dark respiration has little impact on 24-hour integrated ∆13C (0.1‰). We also sampled methane and CO2 from collapse scar bogs (transient permafrost degradation features in permafrost peatlands) to test the hypotheses that microbial respiration and methane production are stimulated by permafrost degradation and collapse and that the fen-like vegetation (i.e. Carex andxi Eriophorum) found in collapse scar bogs near the collapsing edge stimulates acetate fermentation. Our results show that collapse scar bogs have an evolution of spatial variation in methanogenic pathways that is related to surface vegetation cover type. We also demonstrate that changes in stable-isotope fractionation caused by shifts from acetate fermentation and CO2 reduction occur over long time scales (> annual) and are dependent on changes in wetland morphology and surface vegetation cover. We also used radiocarbon as a tracer to test the hypothesis that melting permafrost surrounding the collapse scar bog provides nutrients to the bog-moat location, stimulating the production of radiocarbon-depleted methane. Our results show that the radiocarbon content of methane and DIC at these sites is highly variable and may depend on groundwater input, surface vegetation, and morphological factors associated with the melting permafrost plateau. We conclude that the younger, more labile, carbon stimulating acetate fermentation at one of the sites is supplied by the fen-like surface vegetation, while the older, more recalcitrant, carbon stimulating CO2 reduction at the other site may be supplied by melting permafrost plateau..
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Date Issued: 2005
Identifier: FSU_migr_etd-0429
Format: Thesis

Title: Morphological Barrier Island Changes and Recovery of Dunes after Hurricane Dennis, St. George Island, Florida.
Creator: Priestas, Anthony Michael, Fagherazzi, Sergio, Stallins, J. Anthony, Kish, Stephen, Georgen, Jennifer, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A robust dune system is one of the principal factors in the protection of recreational and residential property within barrier islands. Storm surge from significantly large storm events may remove some or all of the dunes during overwash processes and deposit sediment as washover fans or terraces in the back-barrier. During the summer of 2005, Hurricane Dennis greatly overwashed much of the northwest barrier island chain along the Florida panhandle. The post-storm recovery of dunes and...
Show moreA robust dune system is one of the principal factors in the protection of recreational and residential property within barrier islands. Storm surge from significantly large storm events may remove some or all of the dunes during overwash processes and deposit sediment as washover fans or terraces in the back-barrier. During the summer of 2005, Hurricane Dennis greatly overwashed much of the northwest barrier island chain along the Florida panhandle. The post-storm recovery of dunes and morphological changes occurring after Hurricane Dennis within St. George Island State Park is investigated, in addition to the application of numerical methods as a supplemental tool in determining the post-storm "recovery state" of the barrier and envision morphologic trends. Dune recovery rates are estimated by calculating sediment volume changes of profiles through time. One-dimensional, spatial-series Fourier analysis of individual profiles are used to quantify the recovery and morphologic nature of secondary dunes. Two-dimensional Fourier analysis of elevation data were attempted to be used as a tool to discriminate geomorphic trends in the barrier. Digital elevation models are used to describe post-storm morphologic changes, and the future recovery state of the barrier may be supplemented by analyzing the distributions of curvature and gradients calculated numerically from LIDAR data. Results show that secondary dunes recovered at an average rate of ~3-4 cm per month, and sediment volume changes across transects varied between -1.5 m3/m to1.2 m3/m depending on the presence of vegetation, storm-debris pavement, and proximity to washover deposits. Despite some transects having a net sediment volume loss, all dunes in the presence of vegetation had increased in height. Vegetation did not propagate where storm-debris pavement existed during the one-year duration of the study. The presence of vegetation inhibited dune migration thus favoring dune growth or decreasing the effect of erosion from strong wind events. Fourier analysis of profiles captured changes in dune height at specific wavelengths. The highest energies from the spectra were usually at 30 to 40 meter wavelengths for each profile in time, which reflects the immobility of the dunes and may also reflect the controls of vegetation on dune spacing. The results of two-dimensional Fourier analysis on terrain data were difficult to interpret, but may prove a potential use in terrain analysis. Overwash was prevalent throughout the barrier. For the studied area, St. George Island had experienced inundation overwash with an estimated 100,000 ft3/ft net loss of sediment following the hurricane. Nearly the entire foredune complex was removed, save a few remnants. Storm surge had likely penetrated first in areas where foredunes were either low or discontinuous; in these areas, beach widening was less prevalent. In contrast, the beach widening (~30ft) occurred in areas where the foredunes were higher and more continuous.
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Date Issued: 2009
Identifier: FSU_migr_etd-0458
Format: Thesis

Title: Climatological Characteristics of the Jet Streams over West Africa.
Creator: Suk, Jonathan David, Nicholson, Sharon E., Fuelberg, Henry E., Cai, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This paper examines the climatology of the major jet steams over West Africa. Three prominent jets occur at varying heights in the atmosphere, and while each jet is zonal in its flow, their sizes, magnitudes, and directions vary greatly. The Tropical Easterly Jet is shown to be the strongest and most consistent in its location at approximately 200 to 150 hPa. As its name implies, this jet stream consists of easterly flow and has been the topic of many studies over the Tibetan Plateau and...
Show moreThis paper examines the climatology of the major jet steams over West Africa. Three prominent jets occur at varying heights in the atmosphere, and while each jet is zonal in its flow, their sizes, magnitudes, and directions vary greatly. The Tropical Easterly Jet is shown to be the strongest and most consistent in its location at approximately 200 to 150 hPa. As its name implies, this jet stream consists of easterly flow and has been the topic of many studies over the Tibetan Plateau and Indian Ocean due to its relationship with the Indian Monsoon. On a smaller scale, the African Easterly Jet is prominent over West Africa at approximately 700 to 600 hPa. Although it is associated with the African Monsoon, its strength is related to the temperature contrast between the dry desert to its north, and the cool, moist south-westerlies to the south. The third jet stream is the only one that is westerly in direction. It is the least studied of the three jets. The Low Level Westerlies are located between 1000 and 850 hPa. Although they exhibit a smaller velocity, they are believed to exert a significant influence on the precipitation pattern over West Africa. The goal of this project is to determine the climatological characteristics of the three jet streams, especially during the summer months of June, July, August, and September. Along with building a database to analyze the climatological trends of the jets, their interrelationships are also studied. The speed of the Low Level Westerlies is shown to have a significant correlation with the speed of the Tropical Easterly Jet. And, although the African Easterly Jet occurs in the center of the atmospheric column between the other two jets, it does not have a significant relationship to either of the jets located above and below. The conclusions of this paper naturally lend themselves to further research to help explain not only the reason why the Tropical Easterly Jet and the Low Level Westerlies are related, but also the influence that these systems have on the local environment. In addition, future research should determine the larger scale implications of each jet's location in relation to the other jet streams
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Date Issued: 2007
Identifier: FSU_migr_etd-0400
Format: Thesis

Title: Development of the Finite-Volume Dynamical Core on the Cubed-Sphere.
Creator: Putman, William M., O'Brien, James J., Lin, Shian-Jiann, Rood, Richard, Krishnamurti, T. N., Navon, I. Michael, Zou, Xiaolei, Department of Earth, Ocean and Atmospheric Sciences...
Show morePutman, William M., O'Brien, James J., Lin, Shian-Jiann, Rood, Richard, Krishnamurti, T. N., Navon, I. Michael, Zou, Xiaolei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: The finite-volume dynamical core has been developed for quasi-uniform cubed-sphere grids within a flexible modeling framework for direct implementation as a modular component within the global modeling efforts at NASA, GFDL-NOAA, NCAR, DOE and other interested institutions. The shallow water equations serve as a dynamical framework for testing the implementation and the variety of quasi-orthogonal cubed-sphere grids ranging from conformal mappings to those numerically generated via elliptic...
Show moreThe finite-volume dynamical core has been developed for quasi-uniform cubed-sphere grids within a flexible modeling framework for direct implementation as a modular component within the global modeling efforts at NASA, GFDL-NOAA, NCAR, DOE and other interested institutions. The shallow water equations serve as a dynamical framework for testing the implementation and the variety of quasi-orthogonal cubed-sphere grids ranging from conformal mappings to those numerically generated via elliptic solvers. The cubed-sphere finite-volume dynamical core has been parallelized with a 2-dimensional X-Y domain decomposition to achieve optimal scalability to 100,000s of processors on today's high-end computing platforms at horizontal resolutions of 0.25-degrees and finer. The cubed-sphere fvcore is designed to serve as a framework for hydrostatic and non-hydrostatic global simulations at climate (4- to 1-deg) and weather (25- to 5-km) resolutions, pushing the scale of global atmospheric modeling from the climate/synoptic scale to the meso- and cloud-resolving scale.
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Date Issued: 2007
Identifier: FSU_migr_etd-0511
Format: Thesis

Title: Statistical Prediction of Tropical Cyclone Intensity Using Dynamical and Thermodynamical Inner-Core Parameters Derived from Hwrf Analysis and Forecasts.
Creator: Zelinsky, David A., Co-, T.N. Krishnamurti, Co-, Paul Ruscher, Misra, Vasu, Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A new multiple linear regression model for short range tropical cyclone intensity prediction is developed. Four new dynamical and thermodynamical predictors based on HWRF output are considered: (1) the horizontal advection of relative angular momentum, (2) energy exchange from the divergent to the rotational kinetic energy (Psi-Chi interactions), (3) the conversion of shear vorticity to curvature vorticity, and (4) the vertical differential of heating in the complete potential vorticity...
Show moreA new multiple linear regression model for short range tropical cyclone intensity prediction is developed. Four new dynamical and thermodynamical predictors based on HWRF output are considered: (1) the horizontal advection of relative angular momentum, (2) energy exchange from the divergent to the rotational kinetic energy (Psi-Chi interactions), (3) the conversion of shear vorticity to curvature vorticity, and (4) the vertical differential of heating in the complete potential vorticity equation. Predictors were calculated using Hurricane Research Weather and Forecast (HWRF) model initial fields. Each predictor was determined to exhibit a statistically significant relationship with 12 hour intensity change in tropical cyclones by an F-test. The predictors were then used as the basis for a multiple linear regression model, following the methodology of the operational Statistical Hurricane Intensity Prediction Scheme (SHIPS). Four additional predictors, intended to represent basic storm information and environmental conditions, were included in the development of a second model. Retrospective forecasts of hurricanes in 2004, 2005, and 2006 were created for both models, and compared to operational SHIPS and HWRF forecasts. Despite relying on HWRF fields for the calculation of predictors, the new model produces better forecasts than HWRF for short term (less than 48-hr) forecasts. Additional methods were developed to extend forecasts beyond 48 hours. This resulted in a systematic improvement of HWRF forecasts. It is proposed that the new model could be used operationally as a new version of the "early" HWRF.
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Date Issued: 2011
Identifier: FSU_migr_etd-0585
Format: Thesis

Title: The Effect of Radiative Transfer on the Atlantic Subtropical Anticyclone and Hurricane Steering.
Creator: Diaz, Dante Christopher, Krishnamurti, T. N., Hart, Robert E., Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study explores sensitivity of the Atlantic subtropical anticyclone and the tracks of tropical cyclones traveling around the subtropical anticyclone to radiative transfer. The data sets for these experiments are derived from 120-hours forecasts generated using the T126 version of the Florida State University Global Spectral Model (FSUGSM). The subtropical anticyclone owes its origin, maintenance, and its asymmetrical nature over the Atlantic Ocean mainly due to radiative cooling over the...
Show moreThis study explores sensitivity of the Atlantic subtropical anticyclone and the tracks of tropical cyclones traveling around the subtropical anticyclone to radiative transfer. The data sets for these experiments are derived from 120-hours forecasts generated using the T126 version of the Florida State University Global Spectral Model (FSUGSM). The subtropical anticyclone owes its origin, maintenance, and its asymmetrical nature over the Atlantic Ocean mainly due to radiative cooling over the eastern ocean. This being the case, it follows that the way radiative properties are modeled will play a crucial role in determining the reliability of a forecast. In order to examine this, the full FSUGSM is compared to a version with no radiative properties. This represents the most extreme case and shows the significance of radiative properties on not only the subtropical anticyclone, but also the flow associated with it, and thus the tracks of tropical cyclones traversing the Atlantic Ocean. Since the subtropical anticyclone is the dominant factor in the steering flow, it follows that changes in the tropical cyclones' tracks occur in concert with changes seen in the anticyclone under different radiative conditions. The effects of (no) radiation take about three days to manifest themselves. The subtropical high weakens, and broadens westward without radiative cooling to maintain it. In turn, the orientation of the subtropical high changes as does the steering pattern. Due to this there is a change seen in the tracks of the tropical cyclones. The cyclones are more to the west and south compared to the normal model. Thus, radiation is an important factor in the forecasts of tropical cyclones and their steering environment three days or greater.
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Date Issued: 2007
Identifier: FSU_migr_etd-0738
Format: Thesis

Title: Effect Hypoxia Has on Feeding and Egg Production Rates of Acartia Tonsa Dana 1849 (Copepoda: Calanoida).
Creator: Sedlacek, Chris, Marcus, Nancy, Thistle, David, Kostka, Joel, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Low oxygen conditions in the water column or hypoxia occur in estuaries and impact more than just the obvious commercially important species. Copepods are an important link in the food web and the influence of hypoxia upon them is relatively unstudied. Using the copepod Acartia tonsa, a study of the impact of hypoxia on egg production and feeding was conducted. A. tonsa decreased egg production at lower dissolved oxygen concentrations (DO), with the lowest egg production occurring at 0.53-ml...
Show moreLow oxygen conditions in the water column or hypoxia occur in estuaries and impact more than just the obvious commercially important species. Copepods are an important link in the food web and the influence of hypoxia upon them is relatively unstudied. Using the copepod Acartia tonsa, a study of the impact of hypoxia on egg production and feeding was conducted. A. tonsa decreased egg production at lower dissolved oxygen concentrations (DO), with the lowest egg production occurring at 0.53-ml/l O2 concentration. However as the DO decreased the amount of chlorophyll a in the gut of the copepods increased. Also as DO decreased the number of fecal pellets decreased, indicating that feeding was being suppressed. Another experiment was conducted to determine if by increasing food concentration the affect of hypoxia could be mitigated. The results indicate that increased food did not offset the impact hypoxia has on egg production of A. tonsa. These results suggest that as A. tonsa experiences hypoxia in the wild, population numbers will decrease. Thus if hypoxic conditions increase in scope and duration declines in copepod abundance may very well lead to a decline in the abundance of species that depend on them as food. These species may be of commercial importance.
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Date Issued: 2003
Identifier: FSU_migr_etd-0285
Format: Thesis

Title: Characteristics of Decaying Storms during Lightning Cessation at Kennedy Space Center and Cape Canaveral Air Force Station.
Creator: Anderson, Holly Alison, Fuelberg, Henry E., Ruscher, Paul H., Hart, Robert E., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Improved knowledge of thunderstorm behavior near the end of its lifecycle is essential to improving the prediction of lightning cessation. This study documents the characteristics of decaying storms near the end of their lightning activity at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). Total lightning data were obtained by combining information from the Lightning Detection and Ranging (LDAR) network with the Cloud-to-Ground-Surveillance System (CGLSS) and the...
Show moreImproved knowledge of thunderstorm behavior near the end of its lifecycle is essential to improving the prediction of lightning cessation. This study documents the characteristics of decaying storms near the end of their lightning activity at Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS). Total lightning data were obtained by combining information from the Lightning Detection and Ranging (LDAR) network with the Cloud-to-Ground-Surveillance System (CGLSS) and the National Lightning Detection Network (NLDN). The lightning data were used in conjunction with WSR-88D radar data and Rapid Update Cycle (RUC) model analyses. The study focuses on a dataset of 116 isolated unicellular and multicellular storms during the warm-seasons (May-September) of 2000-2005. Twenty of the 116 storms were tracked through lightning cessation using the K-Means storm clustering and tracking algorithm within the Warning Decision Support System – Integrated Information (WDSS-II). This tracking yielded time-series of radar-derived, RUC-derived, and lightning parameters. Flash characteristics of the 116 storms showed trends during storm growth and dissipation; however, none exhibited clear relationships with the final flash. Although most storms experienced gradually decaying flash rates until cessation, two other cessation behaviors also were observed, making flash activity an unreliable indicator of cessation. Trends in composite reflectivity, reflectivity at three temperatures crucial to storm electrification (i.e., 0°C, -10°C, -20°C), storm thickness of 30 dBZ above -10°C, and vertical gradients of reflectivity were analyzed for 20 storms during the 8 min period prior to cessation to determine if any indicated imminent cessation. Results showed substantial variability in the decaying storms. Although these parameters decreased in most storms during the 8 min period, some increased. Distributions of the parameters at the last flash also were considered, but no clearly preferred value was evident at the last flash. Neither the inversion of lightning initiation criteria (e.g., 40 dBZ at -10°C) nor the descent of 45 dBZ below -10°C were found to be a useful indicator of cessation. Previously-documented lightning "bubbles" of LDAR sources were observed and were consistent with pulses in the intensifying updrafts. The last lightning "bubble" signatures were found to precede lightning cessation by ~35 min.
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Date Issued: 2010
Identifier: FSU_migr_etd-0197
Format: Thesis

Title: Variability of Intraseasonal Precipitation Extremes Associated with ENSO in Panama.
Creator: Arrocha, Gloria, O'Brien, James J., Ruscher, Paul, Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Extensive analysis has been conducted over past decades showing the impacts of El Niño-Southern Oscillation (ENSO) on various regions throughout the world. However, these studies have not analyzed data from many stations in Panama, or they have not analyzed long periods of observations. For these reasons, they often miss climatological differences within the region induced by topography, or they do not possess enough observations to adequately study its climatology. Accordingly, the current...
Show moreExtensive analysis has been conducted over past decades showing the impacts of El Niño-Southern Oscillation (ENSO) on various regions throughout the world. However, these studies have not analyzed data from many stations in Panama, or they have not analyzed long periods of observations. For these reasons, they often miss climatological differences within the region induced by topography, or they do not possess enough observations to adequately study its climatology. Accordingly, the current study focuses on ENSO impacts on precipitation specific to the Isthmus of Panama. Results will be useful for agricultural and water resources planning and Panama Canal operations. Monthly total precipitation data were provided by Empresa de Transmisión Eléctrica S.A., which includes 32 stations with records from 1960 to 2004. The year is split into three seasons: two wet seasons (Early and Late Wet), one dry season (Dry). The country is also divided into regions according to similarities in the stations' climatology and geographic locations. Upper and lower precipitation extremes are associated with one of the three ENSO phases (warm, cold or neutral) to estimate their percentages of occurrences. The differences between each ENSO phases' seasonal precipitation distributions are statistically examined. Statistical analyses show effects of ENSO phases that vary by season and geographical region. Cold and warm ENSO years affect the southwestern half of the country considerably during the Late Wet season. Cold ENSO phases tend to increase rainfall, and the warm phase tends to decrease it. The opposite is true for the Caribbean coast. The Dry season experiences drier conditions in warm ENSO years, and the Early Wet season does not show any statistically significant difference between ENSO years' rainfall distributions.
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Date Issued: 2006
Identifier: FSU_migr_etd-0237
Format: Thesis

Title: Attributing Contributions to the Seasonal Cycle of Anthropogenic Warming in a Simple Radiative- Convective Global Energy Balance Model.
Creator: Sejas, Sergio A., Cai, Ming, Ellingson, Robert G., Wu, Zhaohua, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A simple one-dimensional seasonal atmosphere-ocean energy balance model is used to study the seasonal and latitudinal response of the model climate to a doubling of the CO2 concentration. A new climate feedback analysis method, formulated in Lu and Cai (2009a), is used to isolate contributions (partial temperature changes) of the external forcing alone and subsequent feedbacks to the total temperature change experienced by the model climate. In this study, the relative importance of the...
Show moreA simple one-dimensional seasonal atmosphere-ocean energy balance model is used to study the seasonal and latitudinal response of the model climate to a doubling of the CO2 concentration. A new climate feedback analysis method, formulated in Lu and Cai (2009a), is used to isolate contributions (partial temperature changes) of the external forcing alone and subsequent feedbacks to the total temperature change experienced by the model climate. In this study, the relative importance of the external forcing alone (the CO2 doubling), surface ice-albedo feedback, water vapor feedback, changes in poleward heat transport, changes in vertical sensible heat flux, and changes in heat storage are analyzed. The partial temperature change due to the water vapor feedback is substantially the largest contributor to the globally averaged surface warming. The ice-albedo feedback plays a smaller role, but also significantly contributes to the overall warming of the surface. The most important negative feedback, counteracting the surface warming, is the change in the vertical sensible heat flux. However, though the water vapor feedback is most responsible for the overall surface warming, it is not the feedback most responsible for the seasonal and spatial pattern of the surface warming. The climate of this model indicates that there is a surface polar warming amplification, with a maximum occurring in late summer/early fall. The feedback most responsible for this polar warming amplification and seasonal pattern in this model is the surface ice-albedo feedback, which is largest at high latitudes in summer.
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Date Issued: 2011
Identifier: FSU_migr_etd-0278
Format: Thesis

Title: Impacts of Deep-Sea Carbon Sequestration and of Ciliate Epibionts on Harpacticoid Copepods.
Creator: Sedlacek, Linda, Thistle, David, Wulff, Janie, Marcus, Nancy, Huettel, Markus, Burnett, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: One way to slow down global warming is to reduce the amount of carbon dioxide released into the atmosphere by capturing carbon dioxide from point sources (e.g., power plants) and storing it out of contact with the atmosphere. One storage site that is being considered is the deep-sea floor. Below ~2600 m, carbon dioxide is a liquid and is denser than seawater, so carbon dioxide poured into a depression would create a carbon dioxide lake. The environmental consequences of this disposal option...
Show moreOne way to slow down global warming is to reduce the amount of carbon dioxide released into the atmosphere by capturing carbon dioxide from point sources (e.g., power plants) and storing it out of contact with the atmosphere. One storage site that is being considered is the deep-sea floor. Below ~2600 m, carbon dioxide is a liquid and is denser than seawater, so carbon dioxide poured into a depression would create a carbon dioxide lake. The environmental consequences of this disposal option are largely unknown. This study tries to address the environmental consquences by studying the effects of carbon dioxide-rich seawater on organisms at various distance from a carbon-dioxide source. Harpacticoids were chosen as the study organism because they are abundant and may be an important prey item in the deep sea. To determine if the carbon dioxide-rich seawater affected the harpacticoids, a seven metrics were used. Overall, none of the metrics indicated that exposure to carbon dioxide-rich seawater had an effect. A previous study found a very different result. A comparison of the two studies revealed that the difference in flow dynamics between the two stations in the two experiments could explain the dichotomy, raising the possibility that deep-sea benthic environments that experience slower flow may be better disposal sites. Harpacticoids in the deep-sea sometimes harbor ciliate epibionts. Their presence may influence a harpacticoid's ability to deal with the stress imposed by carbon-dioxide rich seawater. As a first step in trying to understand the harpacticoid-epibiont relationship, I identified the epibionts and determined whether or not they occurred more frequently on adults, on one host species more than the others, on one host sex more than another, or on one portion of a host more than another portion at the control site. Three epibiont species were abundant enough to analyze, Loricophrya sp., Trachelolophos sp., and Vorticella sp. Loricophrya sp. and Trachelolophos sp. individuals attached only to the antennules of Nitokra sp. and occurred significantly more often on this species than on other species. Vorticella sp. individuals attached significantly more frequently to Ameira sp. and Mesocletodes cf. irrasus than to other species. Individuals of Vorticella sp. were found attached to the side of the cephalosome, to the region of the mouth parts, and to the body between the swimming legs. Specificity in host usage was unexpected because harpacticoid individuals of a given species are sparse in the deep-sea. I did not find that any of the epibiont species occurred on one sex more than the other. One method that epibionts may use in order to be host specific is to attach to species that are relatively abundant. I then examined the potential effect that the epibionts had on their hosts. To do so, I compared the harpacticoids at the 2-m site (treatment area) and 75-m site (control area). I found that only for individuals of Nitokra sp. with individuals of Loricophrya sp. attached was there a significantly higher proportion of host individuals with epibionts in the treatment area than in the control area. None of the host species showed a difference in the average number of epibionts they carried in the control area and the treatment area. These results suggest that individuals of Nitokra sp. were capable of resisting the attachment of the first individual of Loricophrya sp., but that individuals of Nitokra sp. were unable to continue to resist after the first Loricophrya sp. individual attached. Trachelolophos sp. was always with Loricophrya sp., so for the analyses that examined the proportion of host individuals that were alive at the time of collection, the group of harpacticoids that had only Loricophrya sp. (= L.) and those with both Trachelolophos sp. and Loricophrya sp. (= L. + T.) were analyzed together (= L. and L. + T.). In the treatment area, the proportion of individuals of Nitokra sp. that were alive at the time of collection was greater when individuals of L. and L. + T. were attached than when they not. In the control area, the proportion of individuals of Ameira sp. that were alive at the time of collection was greater when individuals of Vorticella sp. were attached than when they were not. In general, the effect of the epibionts on their host harpacticoids appears to be positive, an unexpected result considering that positive effects have not been found before.
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Date Issued: 2007
Identifier: FSU_migr_etd-0284
Format: Thesis

Title: The Biochemical Composition of Naupii Derived from Stored Non-Diapause and Diapause Copepod Eggs and the Biology of Diapausing Eggs.
Creator: Sedlacek, Christopher, Marcus, Nancy, Keller, Laura, Thistle, David, Huettel, Markus, Kostka, Joel, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Mariculture of fish is needed to support our ever growing global population. Copepods are a natural and beneficial source of first feed for many marine fish species, but it can be difficult to hatch enough when the fish are ready to feed. Therefore, storage of copepod eggs for use at a later date increases the potential of nauplii to be used as a commercial food source. There are two types of eggs produced by copepods: diapause and non-diapause (or subitaneous). However, little is known about...
Show moreMariculture of fish is needed to support our ever growing global population. Copepods are a natural and beneficial source of first feed for many marine fish species, but it can be difficult to hatch enough when the fish are ready to feed. Therefore, storage of copepod eggs for use at a later date increases the potential of nauplii to be used as a commercial food source. There are two types of eggs produced by copepods: diapause and non-diapause (or subitaneous). However, little is known about diapause or the effects and duration of storage, either under cold or warm temperature conditions, on the biochemical composition of nauplii. Little is also known about the development of embryos that enter diapause. Diapause requires a refractory period before development of the embryo continues. The refractory period can last for several months regardless of environmental conditions. I studied the effects of both cold storage and cold storage with the addition of antibiotics on non-diapause eggs of the copepod Acartia tonsa and duration of storage for diapause eggs produced by Centropages hamatus and compared those results to nauplii derived from non-diapause eggs. The organic components analyzed to determine if potential changes were occurring during storage were lipids, fatty acids, proteins, free amino acids, and carbohydrates as well as the percent hatch of the eggs and the dry weight of the resultant nauplii. To understand diapause, we utilized two stains, one to determine the number of nuclei present and another to determine intracellular pH of the diapausing eggs. Acartia tonsa eggs stored for up to15 days at 1°C did not indicate any change in the biochemical make-up of the resulting nauplii. The only change we observed was in the viability of the eggs, which decreased at a steady rate over time. The viability of the eggs quickly approached zero percent hatch beyond 15 days. The addition of the antibiotic oxytetracyclin at a 10% concentration did not change the naupliar biochemistry and did not increase viability over the storage time. Centropages hamatus eggs maintained a high level of viability over the course of 13 months of storage under anoxic conditions. The nauplii derived from the diapause eggs stored at 25°C had similar biochemical components regardless of the length of the storage period. My study indicates that storage of A. tonsa and C. hamatus may not affect the nutritional value of the nauplii for aquaculture purposes. We also determined that the embryos of C. hamatus stopped developing after ~7 cleavages. The diapausing embryos also maintained an intracellular pH similar to the surrounding water and acidified when beginning to develop. This is the first time the intracellular pH and only the third time the nuclei of a copepod diapausing egg has been determined. This information could allow future researchers to interrupt diapause and induce the eggs to hatch before the end of the refractory period.
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Date Issued: 2008
Identifier: FSU_migr_etd-0283
Format: Thesis

Title: Trends in Maximum and Minimum Temperature Deciles in Select Regions of the United States.
Creator: Smith, Rebecca Anne, O'Brien, James J., Bourassa, Mark A., Ruscher, Paul H., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Daily maximum and minimum temperature data from 758 COOP stations in nineteen states are used to create temperature decile maps. All stations used contain records from 1948 through 2004 and could not be missing more than 5 consecutive years of data. Missing data are replaced using a multiple linear regression technique from surrounding stations. For each station, the maximum and minimum temperatures are first sorted in ascending order for every two years (to reduce annual variability) and...
Show moreDaily maximum and minimum temperature data from 758 COOP stations in nineteen states are used to create temperature decile maps. All stations used contain records from 1948 through 2004 and could not be missing more than 5 consecutive years of data. Missing data are replaced using a multiple linear regression technique from surrounding stations. For each station, the maximum and minimum temperatures are first sorted in ascending order for every two years (to reduce annual variability) and divided into ten equal parts (or deciles). The first decile represents the coldest temperatures, and the last decile contains the warmest temperatures. Patterns and trends in these deciles can be examined for the 57-year period. A linear least-squares regression method is used to calculate best-fit lines for each decile to determine the long-term trends at each station. Significant warming or cooling is determined using the Student's t-test, and bootstrapping the decile data will further examine the validity of significance. Two stations are closely examined. Apalachicola, Florida shows significant warming in its maximum deciles and significant cooling in its minimum deciles. The maximum deciles seem to be affected by some localized change. The minimum deciles are discontinuous, and the trends are a result of a minor station move. Columbus, Georgia has experienced significant warming in its minimum deciles, and this appears to be the result of an urban heat-island effect. The discontinuities seen in the Apalachicola case study illustrate the need for a quality control method. This method will eliminate stations from the regional analysis that experience large changes in the ten-year standard deviations within their time series. The regional analysis shows that most of the region is dominated by significant cooling in the maximum deciles and significant warming in the minimum deciles, with more variability in the lower deciles. Field significance testing is performed on subregions (based on USGS 2000 land cover data) and supports the findings from the regional analysis; it also isolates regions, such as the Florida peninsula and the Maryland/Delaware region, that appear to be affected by more local forcings.
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Date Issued: 2007
Identifier: FSU_migr_etd-0357
Format: Thesis

Title: Assimilation of GPS Radio Occultation Observations.
Creator: Shao, Hui, Zou, Xiaolei, Navon, Ionel M., Liu, Guosheng, Ray, Peter S., Krishnamurti, T. N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Unlike conventional and satellite observations, the Global Positioning System (GPS) radio occultation (RO) techniques provide all-weather, high-vertical-resolution observations that require no calibration. In this dissertation, the assimilation of GPS RO data is studied using the National Centers for Environmental prediction (NCEP) three dimensional variational analysis system. Three GPS data assimilation choices are considered and compared. A set of GPS bending angle assimilation (BA)...
Show moreUnlike conventional and satellite observations, the Global Positioning System (GPS) radio occultation (RO) techniques provide all-weather, high-vertical-resolution observations that require no calibration. In this dissertation, the assimilation of GPS RO data is studied using the National Centers for Environmental prediction (NCEP) three dimensional variational analysis system. Three GPS data assimilation choices are considered and compared. A set of GPS bending angle assimilation (BA) experiments is first carried out and sensitivity of BA results to the observational weighting, the quality of the background fields, the variation of the gravity, and the vertical resolution of the GPS data are investigated. The GPS local refractivity assimilation (REF) is then conducted and compared with BA. Although REF is computationally cheaper than BA, the bias and root mean square errors of the background fields are more significantly reduced by BA than REF. Differences between GPS refractivity and bending angle assimilations are larger in thick-layered cloud systems (e.g., convective clouds in the mid-latitudes and cumulus clouds in the tropics) than in thin clouds and clear sky, which are found to be associated with the strength of horizontal gradient of the atmospheric refractivity. Aiming at achieving both accuracy and computational efficiency, a new observation operator that simulates the GPS excess phase delay is proposed and tested for GPS RO data assimilation. Using the excess phase delay, the along-track refractivity and refractivity gradient information can be included while the computational cost is kept low. Numerical results from the forward simulation and data assimilation using the excess phase delay (PHA) are compared with those of REF. PHA tends to produce a warmer and wetter model atmosphere, with finer structures and larger radii of influence than REF. Compared to GPS observations, simulations and analyses produced by PHA are more accurate than those of REF. It is also pointed out that under the assumption of the spherical symmetry of the local refractivity, the observation operator for the excess phase delay simplifies into a point scheme in which only a vertical profile of model refractivity is required.
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Date Issued: 2005
Identifier: FSU_migr_etd-0301
Format: Thesis

Title: Evaluating the Aerosol First Indirect Effect Using Satellite Data.
Creator: Shao, Hongfei, Liu, Guosheng, Song, Kai-Sheng, Ellingson, Robert G., Fuelberg, Henry, Kim, Kwang-Yul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: First proposed by Twomey, the aerosol first indirect effect hypothesizes that increased aerosol concentration leads to a larger number of cloud condensation nuclei, and therefore smaller but more numerous cloud droplets, which results in greater reflection of incoming solar radiation. It is known that this phenomenon has a net effect to cool the Earth radiatively and offset a substantial amount of the warming caused by the increasing of greenhouse gases. However, the magnitude of this effect...
Show moreFirst proposed by Twomey, the aerosol first indirect effect hypothesizes that increased aerosol concentration leads to a larger number of cloud condensation nuclei, and therefore smaller but more numerous cloud droplets, which results in greater reflection of incoming solar radiation. It is known that this phenomenon has a net effect to cool the Earth radiatively and offset a substantial amount of the warming caused by the increasing of greenhouse gases. However, the magnitude of this effect has been very uncertain. For example, discrepancies of more than a factor of 2 have been reported among various observational results. This uncertainty is a major hurdle in advancing our understanding of how humans have altered, and may in the future alter the Earth's climate. One of the difficulties in deriving the magnitude of this effect from observational data arises from the fact that the aerosol abundance often varies coherently with meteorological conditions, which makes it extremely hard to distinguish between the changes in cloud microphysical parameters caused by varying aerosol concentration and by varying meteorological conditions. Therefore, the goal of this study is to find a reliable method to extract the real strength and to narrow the uncertainty in the estimates of the indirect radiative effect of aerosols. To achieve this goal, first, a satellite visible/near-infrared algorithm is developed to retrieve cloud optical depth and effective radius simultaneously at solar wavelengths (0.63 and 1.61 mm), and a satellite microwave algorithm is developed to retrieve liquid water path in the microwave range (19 and 37 GHz). Using these algorithm we derive cloud microphysical variables in relation to the aerosol first indirect effect. Second, a drizzle index is introduced to discriminate the drizzle clouds from non-drizzle clouds from satellite, which ensures our estimation of the first indirect effect not being contaminated by precipitation related processes. Third, using an analytical model, we have explained how the coherent nature between cloud depth and aerosol concentration as observed in the northeastern Pacific causes misidentification of the aerosol first indirect effect. Finally, we have further explained that the coherent variation between aerosol abundance and meteorological conditions is the major cause responsible for the large discrepancies among various observed values of the aerosol first indirect effect published in literature. We found that clouds in clean areas tend to deviate more from adiabatic process than clouds in polluted area near the coast, which causes an artifact term in commonly-used methods for deriving the aerosol first indirect effect. By introducing a new method capable of removing this artifact, the real strength of the aerosol first indirect effect is assessed over the region of Northeast Pacific. It shows that the magnitude of the aerosol first indirect effect measured by the new parameter is about half of that originally estimated by Twomey
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Date Issued: 2006
Identifier: FSU_migr_etd-0302
Format: Thesis

Title: Lightning Observations during Tropical Cyclone Intensity Change: A Composite Study of Spatial and Temporal Relationships.
Creator: Austin, Marcus, Fuelberg, Henry, Hart, Robert, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Although tropical cyclone (TC) track forecasts have improved considerably in recent years, predicting their intensity continues to be a challenge for both meteorologists and numerical models. A storm's path is primarily influenced greatly by large-scale atmospheric circulations; however, its strength appears to be dominated both by large scale influences and small-scale mechanisms within the storm itself. Most previous research on TC intensity change has employed either numerical modeling or...
Show moreAlthough tropical cyclone (TC) track forecasts have improved considerably in recent years, predicting their intensity continues to be a challenge for both meteorologists and numerical models. A storm's path is primarily influenced greatly by large-scale atmospheric circulations; however, its strength appears to be dominated both by large scale influences and small-scale mechanisms within the storm itself. Most previous research on TC intensity change has employed either numerical modeling or diagnostic approaches using traditional meteorological parameters. Only recently have studies begun to examine electrification as a means for assessing the potential for intensification. Several papers have considered lightning as a proxy for storm intensification, mostly using data from Vaisala's National Lightning Detection Network (NLDN) and Long-Range Lightning Detection Network (LLDN). However, they mostly have examined individual TCs. This study uses LLDN data to study 45 Atlantic Basin TCs between the years 2004 and 2008. Using the National Hurricane Center's (NHC) best track dataset, lightning data are collected for each TC out to a 500 km radius. Parameters including storm intensity, intensity change, environmental vertical wind shear, storm motion, and flash count are compiled at each NHC best track position. The data at each position then are categorized in several ways, including change in intensity. These methods allow us to examine relations between composites of storm intensity/intensification and convective distribution and frequency. Distributions of cloud-to-ground (CG) flash density with respect to storm motion and speed show that lightning generally is preferred in the TCs' right front and right rear quadrants. Hurricanes produce the greatest flash densities during relatively slow forward motion, while tropical depressions and tropical storms exhibit greater flash densities during faster forward motion. Storm-relative CG flash distributions during weakening, no pressure change, and slow intensification (-5 to 0 hPa 6 h-1) exhibit the same right front and rear quadrant preference as the TC intensity categories. Flash densities are greatest during periods of faster intensification, with a nearly symmetric presentation in the inner core region. When computing flash densities with respect to environmental deep layer wind shear, TCs exhibit a strong preference for lightning in the downshear left and right quadrants of the inner core (0-100 km) and outer rainbands (100-300 km), respectively. Tropical storms and hurricanes best show this relation, with TDs exhibiting a stronger preference for lightning in the downshear right quadrant. Relatively weak wind shear produces greater flash densities in all TC intensity categories. Conversely, storms experiencing strong shear exhibit smaller flash densities in all TC categories due to the disruption of deep convection. During periods of faster intensification, maximum flash densities are located in the inner core, with weakening, no change, and slow intensification periods containing greatest density in the outer rainbands. Average flash rates and flash densities are found to be greatest for weaker TCs (tropical depressions and tropical storms) with smaller flash rates and densities in hurricanes. Considering intensity change, periods of faster intensification exhibit significantly greater flash rates than periods of weakening, no pressure change, and slow intensification. Only weak relations are found between flash rates and intensity change, with the strongest relationship occurring when lightning lags (occurs after) the pressure change period. Lightning preceding (occurring before) the pressure change period exhibits the weakest relationships in all TC intensities. Correlations between CG lightning and sustained wind speed indicate that there is no preferred timing between maximum lightning activity and maximum sustained winds. Instead, maximum correlations occur during periods when greatest lightning activity both precedes and lags the maximum sustained wind. These results indicate that lightning is poorly correlated with intensity change and can be regarded as a poor choice for intensity forecasting.
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Date Issued: 2011
Identifier: FSU_migr_etd-0261
Format: Thesis

Title: A Validation of the FSU/COAPS Climate Model.
Creator: Engelman, Mary Beth, O'Brien, James J., Ahlquist, Jon E., Ruscher, Paul H., LaRow, Timothy E., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study examines the predictability of the Florida State University/Center for Oceanic and Atmospheric Prediction Studies (FSU/COAPS) climate model, and is motivated by the model's potential use in crop modeling. The study also compares real-time ensemble runs (created using persisted SST anomalies) to hindcast ensemble runs (created using weekly updated SST) to asses the effect of SST anomalies on forecast error. Wintertime (DJF, 2 month lead time) surface temperature and precipitation...
Show moreThis study examines the predictability of the Florida State University/Center for Oceanic and Atmospheric Prediction Studies (FSU/COAPS) climate model, and is motivated by the model's potential use in crop modeling. The study also compares real-time ensemble runs (created using persisted SST anomalies) to hindcast ensemble runs (created using weekly updated SST) to asses the effect of SST anomalies on forecast error. Wintertime (DJF, 2 month lead time) surface temperature and precipitation forecasts over the southeastern United States (Georgia, Alabama, and Florida) are evaluated because of the documented links between tropical Pacific SST anomalies and climate in the southeastern United States during the winter season. The global spectral model (GSM) runs at a T63 resolution and then is dynamically downscaled to a 20 x 20 km grid over the southeastern United States using the FSU regional spectral model (RSM). Seasonal, monthly, and daily events from the October 2004 and 2005 model runs are assessed. Seasonal (DJF) plots of real-time forecasts indicate the model is capable of predicting wintertime maximum and minimum temperatures over the southeastern United States. The October 2004 and 2005 real-time model runs both produce temperature forecasts with anomaly errors below 3°C, correlations close to one, and standard deviations similar to observations. Real-time precipitation forecasts are inconsistent. Error in the percent of normal precipitation vary from greater than 100% in the 2004/2005 forecasts to less than 35% error in the 2005/2006 forecasts. Comparing hindcast runs to real-time runs reveals some skill is lost in precipitation forecasts when using a method of SST anomaly persistence if the SST anomalies in the equatorial Pacific change early in the forecast period, as they did for the October 2004 model runs. Further analysis involving monthly and daily model data as well as Brier scores (BS), relative operating characteristics (ROC), and equitable threat scores (ETS), are also examined to confirm these results.
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Date Issued: 2008
Identifier: FSU_migr_etd-0560
Format: Thesis

Title: Determination of the Quantity of Cloud Liquid in Snow Clouds and Its Effect on Masking the Snow Scattering Signature.
Creator: Smith, John Robert, Liu, Guosheng, Bourassa, Mark, Fuelberg, Henry, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Many studies have been conducted on the satellite remote sensing of rainfall, but not on the remote sensing of snowfall. To obtain a global view of snowfall in a timely matter, passive high frequency microwave satellite measurements must be used. Therefore, an accurate algorithm for detecting and retrieving snowfall on a global scale is needed. In developing this algorithm, it is important to account for the snow scattering signature which reduces the upwelling emission signal from the ocean...
Show moreMany studies have been conducted on the satellite remote sensing of rainfall, but not on the remote sensing of snowfall. To obtain a global view of snowfall in a timely matter, passive high frequency microwave satellite measurements must be used. Therefore, an accurate algorithm for detecting and retrieving snowfall on a global scale is needed. In developing this algorithm, it is important to account for the snow scattering signature which reduces the upwelling emission signal from the ocean surface observed at the top of the atmosphere. However, the emission due to cloud liquid will increase the upwelling radiation, therefore masking the snow scattering signature. Thus, cloud liquid within snow clouds must be understood. In this study, data from the Cloud Profiling Radar on CloudSat and AMSR-E on Aqua are used to investigate the quantity of cloud liquid for snowfall events. The relationship between cloud liquid and echo top, cloud thickness, and two-meter air temperature is determined. The quantity of cloud liquid present in stratiform and convective snowfall events is also compared. Using snowfall profiles obtained from the reflectivity profiles provided by CloudSat, the masking effect of cloud liquid on the snow scattering signature on vertical and horizontal brightness temperature is determined for snow events with various surface snowfall rates. The masking effect on a parameter designed to reduce the emission signal due to cloud liquid, the polarization corrected temperature, is also tested.
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Date Issued: 2010
Identifier: FSU_migr_etd-0369
Format: Thesis

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

Title: Development of the Coamps Adjoint Mesoscale Modeling System for Assimilating Microwave Radiances within Hurricanes.
Creator: Amerault, Clark Mathew, Zou, Xiaolei, Navon, Ionel Michael, O'Brien, James J., Liu, Guosheng, Krishnamurti, T.N., Department of Earth, Ocean and Atmospheric Sciences, Florida...
Show moreAmerault, Clark Mathew, Zou, Xiaolei, Navon, Ionel Michael, O'Brien, James J., Liu, Guosheng, Krishnamurti, T.N., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: An adjoint mesoscale modeling system based on the Naval Research Laboratory's Coupled Ocean Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model was created for use in sensitivity and data assimilation experiments. In addition to the tangent linear and adjoint models of the dynamical core of the COAMPS model, the system includes the tangent linear and adjoint models of the boundary layer turbulent kinetic energy, cumulus, and explicit moist physics parameterizations. The...
Show moreAn adjoint mesoscale modeling system based on the Naval Research Laboratory's Coupled Ocean Atmosphere Mesoscale Prediction System (COAMPS) atmospheric model was created for use in sensitivity and data assimilation experiments. In addition to the tangent linear and adjoint models of the dynamical core of the COAMPS model, the system includes the tangent linear and adjoint models of the boundary layer turbulent kinetic energy, cumulus, and explicit moist physics parameterizations. The inclusion of these adjoint model physics schemes allows for assimilation experiments involving rain-affected observations such as microwave radiances. A radiative transfer model which includes the effects of hydrometeors on atmospheric radiation was linked to the adjoint modeling system to assimilate microwave radiance observations. Probability distribution functions of model-produced and SSM/I observed brightness temperatures show that the mesoscale prediction overestimates the areas of precipitation, but overall matches the microwave observations quite well. Furthermore, estimates of vertical background error covariance matrices for the hydrometeor variables were calculated using differences between model forecasts which utilized different explicit moisture schemes. The statistics of the differences between the forecasts were assumed to be the same as the statistics of the background error for these variables. The inverse of these matrices (which are needed for data assimilation) were computed using Singular Value Decomposition. Only the largest singular value was kept in calculating the inverse. This ensured that all of the elements of the inverse matrix were non-negative. Finally, microwave radiance observations for Hurricane Bonnie (1998) were assimilated in a 4-dimensional variational data assimilation framework using the COAMPS adjoint model. The model-produced radiances calculated from the analysis fields after the assimilation process match the observations well for the lower frequency channels which are sensitive to liquid precipitation and water vapor. In the highest frequency channel, where the presence of frozen hydrometeors can have a large impact on the radiance value, the match between the analysis and the observations was not as good. The forecasted hurricane was slightly stronger after the assimilation of microwave radiances in terms of both maximum surface windspeed and minimum central sea level pressure, and some improvement was seen in radiance space as well. More observations from within the hurricane, which will improve the analysis of other variables, will most likely be needed to see a greater forecast impact from the assimilation of these observations.
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Date Issued: 2005
Identifier: FSU_migr_etd-0049
Format: Thesis

Title: Hurricane Surface Wind Model for Risk Management.
Creator: Axe, Lizabeth Marie, Krishnamurti, T. N., Ruscher, Paul H., Cunningham, Philip, Cocke, Steven, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The landfalls of extreme hurricane events in recent years reveal the need for more accurate predictions of winds during landfalling tropical cyclone events to help reduce property damage. The goal of this study is to develop a high-resolution surface wind exposure model that incorporates an effective roughness model. In this study, the wind model calculates flight- level winds of a rankine- like vortex in a simple synthetic large-scale environment at a 1 km resolution. The flight-level winds...
Show moreThe landfalls of extreme hurricane events in recent years reveal the need for more accurate predictions of winds during landfalling tropical cyclone events to help reduce property damage. The goal of this study is to develop a high-resolution surface wind exposure model that incorporates an effective roughness model. In this study, the wind model calculates flight- level winds of a rankine- like vortex in a simple synthetic large-scale environment at a 1 km resolution. The flight-level winds are then reduced to 10 m using a reduction scheme based on GPS dropwindsonde profiles. The roughness component calculates the effective roughness length using a radial weight function based on the source area model developed by Schmid and Oke, with an upwind fetch of 5 km. The weight function is dependent on the distance from sensor, sensor height, surface roughness (approximately 100 m resolution), and the Monin-Obukov length. The weighted average of roughness values is taken over 8 possible wind directions to give a more sophisticated effective roughness length for all land points. The high-resolution wind exposure model provides realistic analyses for hurricane Andrew (1992), Erin (1995), Kate (1985), and Donna (1960) at the time of their Florida landfalls. It is also useful for recreating historical hurricane case studies. There is a potential for further development into a real-time analysis and forecasting tool during tropical cyclone landfall events.
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Date Issued: 2003
Identifier: FSU_migr_etd-0039
Format: Thesis

Title: Post-Processing Improvements to an Ensemble Forecast Using an Archive of Past Forecasts and Verifications.
Creator: Allgood, Adam Douglas, Ahlquist, Jon E., Krishnamurti, T. N., Zou, Xiaolei, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Ensemble forecasts are the primary tool used operationally to assess forecast uncertainty. Studies of ensemble forecasts, however, have shown that forecast verifications too frequently lie outside of the ensemble's range of possibilities, meaning that uncorrected ensemble forecasts suggest more confidence than is justified. To make ensemble forecasts more representative of the actual range of possibilities, we present a technique to post-process ensemble forecasts by replacing member...
Show moreEnsemble forecasts are the primary tool used operationally to assess forecast uncertainty. Studies of ensemble forecasts, however, have shown that forecast verifications too frequently lie outside of the ensemble's range of possibilities, meaning that uncorrected ensemble forecasts suggest more confidence than is justified. To make ensemble forecasts more representative of the actual range of possibilities, we present a technique to post-process ensemble forecasts by replacing member forecasts with verifications of what actually occurred when past forecasts were similar. To maximize the information that can be extracted from an archive of past forecasts and verifications, we allow analogs to come from different locations in space. We evaluated our procedure to post-process NCEP ensemble precipitation forecasts for the United States for 15-day periods in July 2005 and January 2006. Our analog correction technique significantly improved the ensemble's ability to forecast the probability of precipitation, in particular correcting the NCEP Global Ensemble's ``wet' bias at low precipitation amounts. Brier Skill Scores for 6-hour accumulated precipitation during the winter indicated that uncorrected ensemble forecasts were less skillful at predicting the probability of precipitation than forecasting zero precipitation as indicated by negative Brier Skill Scores (roughly -2.5). Post processed forecasts had Brier Skill Scores as high as 0.34. The tendency of the ensemble to underforecast heavy precipitation events, however, was not well corrected by our post-processing technique. Examinations of analog locations during heavy precipitation events indicated that analogs were taken from regions where precipitation patterns differed from those at the forecast point. This indicates that analogs must be chosen using more information than merely the similarity of ensemble precipitation forecasts to past forecasts.
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Date Issued: 2007
Identifier: FSU_migr_etd-0173
Format: Thesis

Title: Improving Hurricane Intensity Forecasts in a Mesoscale Model via Microphysical Parameterization Methods.
Creator: Albers, Cerese Marie, Krishnamurti, Tiruvalam N., Liu, Guosheng, Ruscher, Paul, Hood, Robbie, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Accurate hurricane intensity prediction is at the forefront of atmospheric science today, and improvements to mesoscale modeling of these storms continue to be major components of refining the accuracy of intensity forecasting. The primary goal of this study is to improve mesoscale modeling of hurricane intensity via the comparison of field campaign observations of Hurricane Erin 2001 from the Fourth Convection And Moisture Experiment (CAMEX-4) and Hurricane Dennis 2005 from the Tropical...
Show moreAccurate hurricane intensity prediction is at the forefront of atmospheric science today, and improvements to mesoscale modeling of these storms continue to be major components of refining the accuracy of intensity forecasting. The primary goal of this study is to improve mesoscale modeling of hurricane intensity via the comparison of field campaign observations of Hurricane Erin 2001 from the Fourth Convection And Moisture Experiment (CAMEX-4) and Hurricane Dennis 2005 from the Tropical Cloud Systems and Processes (TCSP) mission with simulated results of improved microphysical parameterization in a mesoscale model that utilizes the Krishnamurti, et al (1991) technique of rain rate initialization (RRI). Comparison of the simulated results with field observations collocated with satellite observations provides a way to validate many different aspects of the simulated hurricane's structure and intensity. The mesoscale model used in this research is the Weather Research & Forecasting (WRF) model version 2.1 (ARW). Much of the existing microphysical parameterization of this model is built from results of mid-latitude observations. Substantial improvement to the model's intensity forecasting in the tropics can be made via proper parameterization of the model microphysics for hurricanes. With a foundation of results from other hurricane mesoscale modeling initial/boundary conditions, dynamics and physics studies, basic options for modeling hurricanes Erin (2001) and Dennis (2005) are chosen and held constant during a series of microphysical sensitivity experiments for each storm. These are specifically designed to isolate the individual effects of altering one microphysical parameter at a time on the hurricane's intensity forecast and are carried out in a doubly or triply nested way. The initial and boundary conditions used in the innermost grid with finer resolution are obtained from the respective outermost grids where rain rate initialization is invoked. All of the results are illustrated for the highest-resolution innermost domain, which is integrated using an explicit microphysics scheme. Each of these experiments are integrated for a forty-eight hour forecast period, adequately capturing the mature and intensification stages of the two hurricanes. Skill scores are obtained from the results of the two sets of experiments. Root Mean Square Errors (RMSE) and Anomaly Correlations (AC) are computed by comparing the model output of each experiment to NCEP's final analysis (fnl) available at one-degree horizontal resolution and six-hour temporal resolution interpolated to the respective model grid. Taking into account the way that each experiment performs in terms of simulated storm intensity as well as optimized RMSE and AC, the optimal combination of microphysical processes (i.e. melting, evaporation, fall speed of hydrometeors) for each storm is determined. Then a final forty-eight hour forecast of each hurricane is made utilizing this optimal microphysical parameterization combination. The results from each final run are compared to observations, skill scores are computed, and the final intensity improvements for both hurricanes Erin and Dennis are shown. The results of this study strengthen the evidence that RRI and proper microphysical parameterization in mesoscale hurricane modeling are both useful and effective techniques, and combine to improve hurricane intensity forecasting in a mesoscale model.
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Date Issued: 2007
Identifier: FSU_migr_etd-0156
Format: Thesis

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

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

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

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

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

Title: Examining Interannual Variability of the Short Rains for Different Categories of Wet and Dry Years.
Creator: Smoleroff, Kaitlyn, Nicholson, Sharon E., Bourassa, Mark Allan, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and...
Show moreSmoleroff, Kaitlyn, Nicholson, Sharon E., Bourassa, Mark Allan, Misra, Vasubandhu, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: East African "shorts rains" variability has long been a subject of interest both for its complexity and its sometimes dire human impacts. Four large-scale factors are thought to influence the shorts rains: Niño 3.4, the IOZM, and the surface and upper-level zonal winds over the central Indian Ocean. Recent research has shown that these established teleconnections are not as robust as previously thought. Particularly, the relationships between the short rains season and these factors have...
Show moreEast African "shorts rains" variability has long been a subject of interest both for its complexity and its sometimes dire human impacts. Four large-scale factors are thought to influence the shorts rains: Niño 3.4, the IOZM, and the surface and upper-level zonal winds over the central Indian Ocean. Recent research has shown that these established teleconnections are not as robust as previously thought. Particularly, the relationships between the short rains season and these factors have broken down since 1982, with several seasons having opposite conditions than what was expected. Furthermore, the debate over which large-scale factors have the most effect on the short rains season is on-going. In this study, the relationship between the interannual variability of the short rains and known large-scale forcing factors is examined with the goal of answering three questions: 1) Are the factors associated with dry and wet conditions different before versus after 1982? 2) Why did dry or wet conditions fail to occur when predicted in recent years? 3) Do dry seasons with different combinations of large-scale factors produce different local patterns in atmospheric circulation? To investigate these questions, different October-November seasons were designated into categories. Analysis was done on several diagnostic variables for each category of rainfall seasons. Contrary to what was expected, zonal wind field results showed few differences between pre- and post-1982, giving little answers as to why the relationships between the short rains and these factors has changed since 1982. Omega results highlight influence of a narrow area of upper-level sinking and rising motion over and just off the coast of East Africa. This study suggests that this feature, while indeed connected to the four established links, could shed new insight on the short rains interannual variability if evaluated as an individual factor. Results also reaffirmed prior research that shows wet and dry conditions have different sensitivities to large-scale factors. Additionally, it was found that different combinations of factors, which all produced dry conditions, had different local atmospheric patterns. Some of the greatest contrasts seen in local patterns were between factor combinations that include the IOZM compared to combinations without it. This suggests that different large-scale factors could counteract each other.
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Date Issued: 2015
Identifier: FSU_2015fall_Smoleroff_fsu_0071N_12811
Format: Thesis

Title: Algorithms for Advanced Tropical Cyclone Visualization.
Creator: Winterbottom, Henry R., Zou, Xiaolei, Erlebacher, Gordon, Bourassa, Mark A., Liu, Gousheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: With the events of recent years - especially in the Atlantic tropical basin, the need for additional forecast tools to aid in tropical cyclone (TC) prediction and understanding is apparent. A suite of algorithms to be used for 3-D TC visualization are presented. Utilizing the assets of the Amira visualization software, we present methods which constitute a real-time visualization routine of TC genesis, mesoscale, and TC centered features derived from the The Florida State University (FSU)...
Show moreWith the events of recent years - especially in the Atlantic tropical basin, the need for additional forecast tools to aid in tropical cyclone (TC) prediction and understanding is apparent. A suite of algorithms to be used for 3-D TC visualization are presented. Utilizing the assets of the Amira visualization software, we present methods which constitute a real-time visualization routine of TC genesis, mesoscale, and TC centered features derived from the The Florida State University (FSU) adaptation of the Pennsylvania State University (PSU) and National Center for Atmospheric Research (NCAR) Fifth Generation Mesoscale Model (MM5). However, the algorithms we develop are generic in that they can be applied to any gridded output from a forecast model. A method for the removal TC vorticity fields allowing an approximation of the environmental steering levels is also developed. The development and use of an adaptive wavenumber refinement filter (AWRF) has proven to outperform various alternative methods for TC vortex removal and thus the preservation of the environmental flow. Case study inter-comparisons are performed and illustrate that the AWRF provides the smallest mean track errors in future forecast position compared to those determined by the model's use of minimum sea level pressure (SLP) and vorticity maxima algorithm for TC center location. Discussions are also provided suggesting areas of needed improvement within the algorithm as illustrated by the case studies presented.
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Date Issued: 2006
Identifier: FSU_migr_etd-0929
Format: Thesis

Title: The Development of Forecast Confidence Measures Using NCEP Ensembles.
Creator: Durante, Andrew Vincent, Hart, Robert, Fuelberg, Henry, Krishnamurti, T.N., Watson, Andrew I., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Ensemble model data can provide a wealth of guidance to forecasters, especially in terms of forecast confidence. A model run where members diverge generally corresponds to a low confidence forecast, while a model run where members converge generally corresponds to a forecast of high confidence. The current NWS graphically based forecasts accessible to the public do not show this measure of uncertainty and thus communicate a false sense of confidence or precision. From August 2004 into 2006,...
Show moreEnsemble model data can provide a wealth of guidance to forecasters, especially in terms of forecast confidence. A model run where members diverge generally corresponds to a low confidence forecast, while a model run where members converge generally corresponds to a forecast of high confidence. The current NWS graphically based forecasts accessible to the public do not show this measure of uncertainty and thus communicate a false sense of confidence or precision. From August 2004 into 2006, approximately 2 years of individual GFS model ensemble data were analyzed. The result is a climatology of each ensemble member, which obviously does not match the observed climatology based on the NCEP reanalysis. The GFS model ensemble climatology was normalized so that there is a mapping between the current model ensemble value and the climatological value. Since there is only two years of data, the climatology is calculated on a 45 day temporal window. This method is similar, but more simplistic, to the method that is used in the FSU Superensemble (Krishnamurti 2000) of using temporal windows to increase climatology robustness in the training dataset. The variables analyzed here include 2-m temperature, 10-m wind speed and 10-m vorticity. Normalized climatology distributions have been calculated for each grid point within the ensemble member, with forecast confidence measures developed by comparing the normalized spread of the ensemble members to the model climatological spread, as described below. This normalized spread is compared to the typical spread for that time of year, location, and forecast length to arrive at a relative measure of forecast uncertainty. If the current model uncertainty is greater (less) than the uncertainty of the model climatology, then there is a lower (higher) than average confidence. Confidence graphics have been developed and analyses to see how confidence values behave with certain synoptic situations are ongoing. This overall behavior along with certain case studies will be featured. It has also been seen that there is a statistical significant difference in NWS forecast error between low confidence and high confidence regimes. Average NWS error for the below (above) normal GFS confidence forecasts was 5.20oF (3.08oF). A student t-test on these values revealed that there is a statistically significant difference to 95% confidence of the mean forecast error during low and high confidence GFS forecasts. That is, the mean WFO forecast error is significantly increased during times of low forecast confidence in the GFS ensemble. Therefore, forecasters have a-priori knowledge of the likely human forecast error when they see the GFS ensemble output-- before the NWS forecast even verifies. During cases of extreme low confidence where the current model standard deviation is greater than the 25-year observational standard deviation, a climatology forecast was found to be more accurate than the overall ensemble mean. Although the confidence graphics are only based on the GFS ensembles as of now, more models will be added in the future to see how they behave when compared to each other. The GFS ensembles and the corresponding confidence technique have been used in the FSU-MM5 to see how a mesoscale model affects the overall confidence for a specific case. Recent feedback from NWS employees suggests an additional development of confidence graphics based on the "poor man's ensemble", which is an ensemble of all the operational forecast models. Eventually these graphics of below and above average confidence may be implemented into the Graphical Forecast Editor (GFE) for use in the National Digital Forecast Database (NDFD).
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Date Issued: 2006
Identifier: FSU_migr_etd-0627
Format: Thesis

Title: Assessing the Potential Impact of Gifts Data to Severe Convective Precipitation Prediction.
Creator: Yorsaner, Mark Evan, Zou, Xiaolei, Hart, Robert, Ruscher, Paul, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A two-phase study of the potential impact of Geosynchronous Imaging Fourier Transfer Spectrometer (GIFTS) radiance data to the prediction of strong convective events was developed. In the first phase of the project, a statistical analysis of six runs of the Fifth Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5), version 3, was performed. These runs incorporate different size domains, numbers of vertical levels, numbers of nesting domains,...
Show moreA two-phase study of the potential impact of Geosynchronous Imaging Fourier Transfer Spectrometer (GIFTS) radiance data to the prediction of strong convective events was developed. In the first phase of the project, a statistical analysis of six runs of the Fifth Generation Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5), version 3, was performed. These runs incorporate different size domains, numbers of vertical levels, numbers of nesting domains, and physical schemes. Using high-resolution National Center for Environmental Prediction (NCEP) Stage IV precipitation estimates, mesonet data, and radar reflectivity, it was determined that of all runs, one was chosen as being most appropriate for simulating GIFTS radiance. This run incorporates the simple ice microphysical scheme, the Grell cumulus scheme, the Blackadar planetary boundary layer scheme, and a simple atmospheric radiation scheme. Furthermore, this run was nested, with the mother domain (12-km resolution) of size 163 x 127 x 54 and the nested domain (4-km resolution) of size 103 x 127 x 54. In the second phase of the project, two sensitivity studies were carried out. In the first sensitivity study, the sensitivity of simulated GIFTS radiance to temperature and water vapor were examined. The 14 most sensitive channels within the GIFTS spectral range, out of 3,073, were chosen for further analysis. Through an analysis of an MM5 grid point that had relatively minimal cloud cover, it was determined that the most sensitive atmospheric layers at eight channels are in the lower troposphere (temperature) and lower to mid-troposphere (water vapor). At the other six, the most sensitive region is in the mid- to upper troposphere. The layers of maximum sensitivity are consistent with peaks of the weighting functions of these channels. The second sensitivity study examined the sensitivity of convective precipitation forecasts to the initial conditions of temperature and water vapor. The purpose of this study was to "bridge" the results of the first sensitivity study to the MM5 quantitative precipitation forecast (QPF) results. It was found that the most sensitive region is over the Central Plains of the United States and that the convective QPF is most sensitive to both water vapor content and temperature in the low-levels of the troposphere. Furthermore, temperature is deemed more sensitive to convective QPFs than water vapor. The results from these sensitivity tests, when linked together, demonstrate that GIFTS radiance at the eight wavenumbers most sensitive in the lower troposphere may be more effective to improve QPF than higher wavenumber radiance and that temperature in the Central Plains is the key meteorological variable to which the convective QPF is most sensitive. In a future four-dimensional variational data assimilation (4D-Var) study, simulated and real atmospheric observations from various sources will be assimilated into the MM5, with the GIFTS model representing the observation operator. Through this current study, a better sense of the utility of data from GIFTS to the forecasting of convective precipitation is ascertained, which would help streamline the 4D-Var study.
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Date Issued: 2005
Identifier: FSU_migr_etd-0856
Format: Thesis

Title: Statistical Forecasting of Florida Monthly Rainfall.
Creator: Wolf, Linden S., Ahlquist, Jon E., Sura, Philip, Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study computes statistical forecasts of monthly and three-monthly rainfall for seven regions of Florida defined by the National Climatic Data Center. First, time-lagged auto- and cross-correlations are computed involving monthly regional rainfall time series and various potential predictors. Various statistical monthly forecasting models are then built for each of the seven regions based on teleconnection indices and principal components of monthly heights of the global 500 hPa pressure...
Show moreThis study computes statistical forecasts of monthly and three-monthly rainfall for seven regions of Florida defined by the National Climatic Data Center. First, time-lagged auto- and cross-correlations are computed involving monthly regional rainfall time series and various potential predictors. Various statistical monthly forecasting models are then built for each of the seven regions based on teleconnection indices and principal components of monthly heights of the global 500 hPa pressure surface. To compare these forecasts to those of the Climate Prediction Center (CPC), the forecasts are categorized into terciles, corresponding to the upper, middle, and lower thirds of the climatological distribution of rainfall for each of the twelve months for each region. Following CPC, these are scored with the Heidke Skill Score. The variability of model coefficients and forecast skill is measured using cross-validation. The monthly Heidke Skill Score is low but generally better than a climatological forecast, which is CPC's standard of comparison. For most months and forecast regions, the Heidke Skill Score increases if a forecast for the middle tercile is replaced by a forecast that all three terciles are equally likely. Averaged over the year, the Florida Panhandle has the lowest monthly forecast skill, and Southwest Florida has the highest. April and May as well as September and October have low skill statewide. These times of year are associated with shifts in the prevailing winds as well as the El Nino-Southern Oscillation (ENSO) phase. Higher skills are obtained when forecasting the next three month's total precipitation than the next month's total precipitation. This increase in skill is largely due to the important of ENSO as a predictor and that ENSO is less noisy across three months than one month. A summer low in the forecast skill for three month's rain is due to the minimum in time-lagged correlation between late spring and summer. A middle tercile forecast for three-month rainfall is more likely to verify than a middle tercile forecast for one-month rainfall.
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Date Issued: 2009
Identifier: FSU_migr_etd-0880
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: Using Chemical Tracers to Evaluate Feeding Habits in Coastal Marine Ecosystems: Stable Isotopes and Organic Contaminants.
Creator: Wilson, Rachel Marie, Chanton, Jeffrey P., Cooper, William T., Nowacek, Douglas P., Kucklick, John R., Wang, Yang, Burnett, William C., Department of Earth, Ocean and...
Show moreWilson, Rachel Marie, Chanton, Jeffrey P., Cooper, William T., Nowacek, Douglas P., Kucklick, John R., Wang, Yang, Burnett, William C., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: The use of chemical tracers to understand ecosystem interactions in the marine environment has gained increasing popularity over the past three decades. Carbon isotope abundances in organic matter sources in the marine system vary significantly making them a useful tracer for discriminating among such sources. Once taken up by primary producers, carbon isotope abundances are conservative throughout the food web. This allows us to measure carbon isotope abundances in secondary (and above)...
Show moreThe use of chemical tracers to understand ecosystem interactions in the marine environment has gained increasing popularity over the past three decades. Carbon isotope abundances in organic matter sources in the marine system vary significantly making them a useful tracer for discriminating among such sources. Once taken up by primary producers, carbon isotope abundances are conservative throughout the food web. This allows us to measure carbon isotope abundances in secondary (and above) consumers and infer organic matter source utilization in the system. Nitrogen isotope abundances, unlike carbon, are not conservative throughout the food web. However, they do fractionate predictably providing a tool by which to measure trophic level of consumer species. Sulfur isotopes, like carbon, differ among sources and are also conservative within the food web providing an additional tracer with which to estimate source contributions. However, concerns about the "dirtiness" of sulfur for analysis purposes put sulfur on the back burner as an ecosystem tracer. With recent improvements in technology and the need for multiple tracers in multi-source systems, sulfur isotope abundance measurements have experienced a resurgence. In this manuscript we use sulfur isotope abundances as a second tracer (with carbon isotope abundances) to estimate organic matter source utilization by consumers in a variety of habitats along the Florida Big Bend coastline. We begin our isotopic analysis of consumers in a Northwest Gulf of Mexico, freshwater dominated estuarine system, Apalachicola Bay, Florida (USA). In Chapter II we evaluate isotopic variation with body size to determine the smallest trophic unit in our system. In Chapter III we develop a concentration-corrected, dual-isotope, multi-source evaluation of organic matter utilization incorporating sulfur as a secondary tracer. We then go on to apply the results of this model to determine trophic level of consumers in Apalachicola Bay based on nitrogen isotope abundance data. In Chapter IV we demonstrate how isotopic variation of sources within a system can confound our interpretations of trophic structure using these methods. We further demonstrate that, in addition to isotopic variation, source inputs and availability may also vary within a given system. This makes comparison among sites more difficult and highlights the need to evaluate isotopic variation in individual systems prior to making comparisons or widespread generalizations about interactions. In Chapter V we apply these methods to a coastal seagrass community. We evaluate isotopic abundances in sources in consumers from the site. Then we apply the mixing model we develop in Chapter II to determine organic matter source utilization by consumers. Finally, we evaluate trophic level of individual consumers and trophic structure of the system based on nitrogen isotopic abundances. We demonstrate that source isotopic abundances differ from those same sources in the freshwater estuarine habitats. We also show that, while benthic organic matter was an important source in Apalachicola Bay, epiphytes provide the major organic matter source supporting consumers in the seagrass habitat. We use source utilization information and trophic level to assign consumers to trophic guilds in this system. The variety of organic matter source utilization is thought to contribute to the high levels of productivity found in this region. In addition to natural tracers, such as isotope abundances, we have also used organic pollutants as tracers of habitat utilization in the Florida Big Bend region. Organic contaminants found in coastal waters include compounds such as DDTs, PCBs, and chlordanes. Although no longer produced in the U.S., their historically wide-spread use and resistance to degradation contributes to their persistence in marine biota. We present data on chemical concentrations and congener profiles in bottlenose dolphins (Tursiops truncatus) and two abundant fish species from this region in Chapter VI. Although this area has been called "pristine" by previous researchers, we demonstrate the relativeness of this term, revealing that even the "forgotten coast" has been influenced by these ubiquitous contaminants. We use these compounds as tracers to evaluate bottlenose dolphin habitat utilization patterns in Florida Big Bend coastal waters. We found that the dolphins we sampled have differences in concentrations and patterns of contaminant loading indicating preference for feeding in specific areas and bays. Our results agree with suggestions based on sighting information that animals from the east and west regions of our study site rarely comingle and that even in the western site, individual animals express preferences for either St Joseph or St Andrews Bay foraging grounds.
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Date Issued: 2010
Identifier: FSU_migr_etd-0901
Format: Thesis

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

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

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

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

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

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

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

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

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

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