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Title: Source Driven Rotating Flow in a Basin with Topography.
Creator: Vijayan Nair Rugminiamma, Linoj, Speer, Kevin G. (Kevin George), Tam, Christopher K. W., Dewar, William K., Florida State University, College of Arts and Sciences, Department of...
Show moreVijayan Nair Rugminiamma, Linoj, Speer, Kevin G. (Kevin George), Tam, Christopher K. W., Dewar, William K., Florida State University, College of Arts and Sciences, Department of Earth, Ocean and Atmospheric Science
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Abstract/Description: Laboratory experiments on a rotating tank of fluid are used to study the fundamental aspects of geophysical fluid flows. The present set of experiments are an attempt to study the effect of a rectangular ridge on the flow of a rotating fluid confined by lateral boundaries and forced by a source. First dye and later Particle Image Velocimetry (PIV) are used to understand the circulation in the domain. A strong southern boundary flow near the western wall of the domain and a cyclonic...
Show moreLaboratory experiments on a rotating tank of fluid are used to study the fundamental aspects of geophysical fluid flows. The present set of experiments are an attempt to study the effect of a rectangular ridge on the flow of a rotating fluid confined by lateral boundaries and forced by a source. First dye and later Particle Image Velocimetry (PIV) are used to understand the circulation in the domain. A strong southern boundary flow near the western wall of the domain and a cyclonic circulation in the trench are observed in these experiments. Overflow from the eastern side to the west of the ridge is seen along the N-S length of the ridge, though the overflow is pronounced near the northern boundary of the domain. Simplified mathematical models are used to describe the observed circulation. Numerical simulations are conducted using the MIT general circulation model on a large scale idealized box domain with a topography similar to the one we used in the laboratory tank as well as a rectangular trench parallel to the eastern wall of the domain. A point mass source contributes to the upwelling at the free surface. This set up represents a homogeneous abyssal layer upwelling slowly due to a polar source. Results indicate a cyclonic sense of circulation and a poleward eastern boundary current over the ridge wall. This intensification can be attributed to the vortex stretching over the slopes of the ridge, as the vertical walls appear in the numerical model as having a steep slope. Friction on vertical walls of the ridge are also a cause of this intensification. Some features of the observed and modeled circulation are compared to the oceanic flow in the deep Pacific Ocean.
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Date Issued: 2019
Identifier: 2019_Spring_VijayanNairRugminiamma_fsu_0071N_15039
Format: Thesis

Title: Circulation in the Lau Basin and Havre Trough.
Creator: Simons, Elizabeth G. (Elizabeth Gabrielle), Speer, Kevin G., Cogan, Nicholas G., Dewar, William K., Sura, Philip, Florida State University, College of Arts and Sciences, Program...
Show moreSimons, Elizabeth G. (Elizabeth Gabrielle), Speer, Kevin G., Cogan, Nicholas G., Dewar, William K., Sura, Philip, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: The ridge systems that frame the Lau Basin and Havre Trough, located east of Fiji and north of New Zealand, separating a large counterclockwise gyre at the surface into two smaller gyres at depth. A strong deep western boundary current (DWBC) has been observed flowing northward, following the Tonga and Kermadec Trench systems, transporting bottom water to the North Pacific. Though circulation has been described to some degree around the Lau Basin and the Havre Trough, these sub-basins have...
Show moreThe ridge systems that frame the Lau Basin and Havre Trough, located east of Fiji and north of New Zealand, separating a large counterclockwise gyre at the surface into two smaller gyres at depth. A strong deep western boundary current (DWBC) has been observed flowing northward, following the Tonga and Kermadec Trench systems, transporting bottom water to the North Pacific. Though circulation has been described to some degree around the Lau Basin and the Havre Trough, these sub-basins have largely been ignored, presumed to act as a barrier to flow and separating the western South Pacific from the eastern South Pacific. An analysis of float data from several sources as well as traditional ship-board hydrographic data reveal a DWBC within the Lau Basin and Havre Trough that is fed by westward flowing jets from breaks within the ridge system. A simple analytical model predicts the large-scale dynamics observed in the basin, and indicates that the topographic structure of the ridge modulates the flow patterns. Sources of water into the Lau Basin and Havre Trough indicate intermediate water sources from the eastern South Pacific, while deep water sources originate to the west. This leads to a revised view of the role of the Lau Basin and Havre Trough with respect to circulation in the South Pacific.
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Date Issued: 2018
Identifier: 2018_Sp_Simons_fsu_0071E_14508
Format: Thesis

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

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

Title: Dissipation of Mesoscale Energy by Vortex-Topography Interaction.
Creator: Bishnu, Siddhartha, Dewar, William K., Chassignet, Eric P., Clarke, Allan J., Kopriva, David A., Florida State University, College of Arts and Sciences, Department of Earth,...
Show moreBishnu, Siddhartha, Dewar, William K., Chassignet, Eric P., Clarke, Allan J., Kopriva, David A., Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Energy is introduced into the oceans primarily at large scales by means of wind, tides and surface buoyancy forcing. This energy is transferred to the smaller mesoscale eld through the geostrophic instability processes. The mesoscale eld appears not to have accelerated appreciably over the last several decades, so we can assume that the mesoscale loses energy at roughly the same rate it receives energy. Interestingly, how the mesoscale loses energy is not quite clear. We have been exploring...
Show moreEnergy is introduced into the oceans primarily at large scales by means of wind, tides and surface buoyancy forcing. This energy is transferred to the smaller mesoscale eld through the geostrophic instability processes. The mesoscale eld appears not to have accelerated appreciably over the last several decades, so we can assume that the mesoscale loses energy at roughly the same rate it receives energy. Interestingly, how the mesoscale loses energy is not quite clear. We have been exploring topographic interaction as a pathway by which the mesoscale may lose energy to unbalanced forward cascading flows. To demonstrate this phenomenon, an approximate model theory is developed which consists of solving a reduced set of the momentum equations in density coordinates for any topographic conguration. The equations are solved using a high order spectral element technique and the results are similar to already published MITgcm simulations.
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Date Issued: 2017
Identifier: FSU_FALL2017_Bishnu_fsu_0071N_14263
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: Circulation and Stirring by Ocean Turbulence.
Creator: Balwada, Dhruv, Speer, Kevin G. (Kevin George), Landing, William M., Dewar, William K., Sura, Phillip, Florida State University, College of Arts and Sciences, Program in...
Show moreBalwada, Dhruv, Speer, Kevin G. (Kevin George), Landing, William M., Dewar, William K., Sura, Phillip, Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: Ocean turbulence is responsible for stirring and spreading ocean tracers, and contributes to the mean circulation as eddy bolus fluxes. The influence of the eddies on the mean circulation becomes particularly important in regions where mean geostrophic flows are weak, such as the meridional flow across the Antarctic Circumpolar Current. However, high resolution observations of eddies and their influence on the circulation are generally lacking, particularly in the deep ocean that cannot be...
Show moreOcean turbulence is responsible for stirring and spreading ocean tracers, and contributes to the mean circulation as eddy bolus fluxes. The influence of the eddies on the mean circulation becomes particularly important in regions where mean geostrophic flows are weak, such as the meridional flow across the Antarctic Circumpolar Current. However, high resolution observations of eddies and their influence on the circulation are generally lacking, particularly in the deep ocean that cannot be observed via satellites. The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) was designed to observe the transport and stirring associated with the eddies in the Southern Ocean, using RAFOS floats and a passive tracer. In the first half of the thesis, the imprint of the eddies on the large scale circulation ([greater than] 100 km) is assumed to be diffusive, and the corresponding eddy diffusivities are quantified using the long term behavior of the RAFOS floats. The eddy diffusivities are found to be suppressed in the presence of mean flows. These eddy diffusivity estimates from DIMES, along with estimates from a couple of other diffusivity studies, are then used to quantify the eddy bolus fluxes in the Southern Ocean, which were found to vary in response to the bottom bathymetry. The second part of this work, addresses the flow at the length scales of the submesoscale and mesoscale ([less than] 100 km). Here, in addition to the DIMES RAFOS floats, we also used surface drifter observations from an experiment, Grand Lagrangian Deployment (GLAD), conducted in the Gulf of Mexico. The goal was to observe the kinematic stirring properties at these smaller scales, and also to characterize the dynamics of the turbulence that is active by investigating the energy spectrum. At the surface ocean in the Gulf of Mexico, we characterized the scale dependent energy distribution over 5 orders of length scales (10 m - 1000 km) using second order velocity structure functions. Divergent motions were found to be dominant, over non-divergent motions, at length scales smaller than 5km, where the Rossby number was greater than one and the third order velocity structure functions indicated the presence of a forward energy cascade. These methods were also used to explain subsurface turbulence in the Southern Ocean with DIMES RAFOS floats. The RAFOS floats showed that divergent flows are also present in the deep ocean at length scales smaller than 30 km, and become comparable in magnitude to the non-divergent flows near 5 km. The observed dispersion of the floats was used to address the question - is the mixing at small scales due mainly to large scale shear (non-local) or small scale eddies (local)? The associated stirring was found to be local at depth.
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Date Issued: 2016
Identifier: FSU_FA2016_Balwada_fsu_0071E_13549
Format: Thesis

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

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

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

Title: Gulf Stream Separation Dynamics.
Creator: Schoonover, Joseph Arthur, Dewar, William K., Kopriva, David A., Chassignet, Eric P., Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences,...
Show moreSchoonover, Joseph Arthur, Dewar, William K., Kopriva, David A., Chassignet, Eric P., Speer, Kevin G. (Kevin George), Florida State University, College of Arts and Sciences, Program in Geophysical Fluid Dynamics
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Abstract/Description: Climate models currently struggle with the more traditional, coarse ( O(100 km) ) representation of the ocean. In these coarse ocean simulations, western boundary currents are notoriously difficult to model accurately. The modeled Gulf Stream is typically seen exhibiting a mean pathway that is north of observations, and is linked to a warm sea-surface temperature bias in the Mid-Atlantic Bight. Although increased resolution ( O(10 km) ) improves the modeled Gulf Stream position, there is no...
Show moreClimate models currently struggle with the more traditional, coarse ( O(100 km) ) representation of the ocean. In these coarse ocean simulations, western boundary currents are notoriously difficult to model accurately. The modeled Gulf Stream is typically seen exhibiting a mean pathway that is north of observations, and is linked to a warm sea-surface temperature bias in the Mid-Atlantic Bight. Although increased resolution ( O(10 km) ) improves the modeled Gulf Stream position, there is no clean recipe for obtaining the proper pathway. The 70 year history of literature on the Gulf Stream separation suggests that we have not reached a resolution on the dynamics that control the current's pathway just south of the Mid-Atlantic Bight. Without a concrete knowledge on the separation dynamics, we cannot provide a clean recipe for accurately modeling the Gulf Stream at increased resolutions. Further, any reliable parameterization that yields a realistic Gulf Stream path must express the proper physics of separation. The goal of this dissertation is to determine what controls the Gulf Stream separation. To do so, we examine the results of a model intercomparison study and a set of numerical regional terraforming experiments. It is argued that the separation is governed by local dynamics that are most sensitive to the steepening of the continental shelf, consistent with the topographic wave arrest hypothesis of Stern (1998). A linear extension of Stern's theory is provided, which illustrates that wave arrest is possible for a continuously stratified fluid.
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Date Issued: 2015
Identifier: FSU_2016SP_Schoonover_fsu_0071E_12967
Format: Thesis

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Title: Variability of Cross-Slope Flow in the Desoto Canyon Region.
Creator: Nguyen, Thanh Tam, Chassignet, Eric P., Dukhovskoy, Dmitry, Huettel, Markus, Morey, Steven L., Dewar, William, Florida State University, College of Arts and Sciences, Department...
Show moreNguyen, Thanh Tam, Chassignet, Eric P., Dukhovskoy, Dmitry, Huettel, Markus, Morey, Steven L., Dewar, William, Florida State University, College of Arts and Sciences, Department of Earth, Ocean, and Atmospheric Science
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Abstract/Description: Cross-slope flow is critical for governing heat and material exchange, including pollutants and biota, between the coastal and deep ocean. This study focuses on characterizing the variability of cross-slope near-bottom flow in the DeSoto Canyon region, where the BP's Macondo well exploded in April 2010, using a multi-decadal HYbrid Coordinate Ocean Model (HYCOM) simulation of Gulf of Mexico circulation. Due to change in shelf orientation east and west of the canyon, wind-driven vertical...
Show moreCross-slope flow is critical for governing heat and material exchange, including pollutants and biota, between the coastal and deep ocean. This study focuses on characterizing the variability of cross-slope near-bottom flow in the DeSoto Canyon region, where the BP's Macondo well exploded in April 2010, using a multi-decadal HYbrid Coordinate Ocean Model (HYCOM) simulation of Gulf of Mexico circulation. Due to change in shelf orientation east and west of the canyon, wind-driven vertical motions are mostly related to a component of the local wind vector along an angle that may deviate from the local isobaths, with smaller deviations from the along-isobath direction to the east of the canyon and bigger departures to the west. This implies that upwelling is associated with along-isobath winds east of the canyon but shelf waves propagating from the eastern shelf, where northwesterly winds are upwelling favorable, influence cross-slope flow to the west of the canyon. Beyond the shelf break, where the Loop Current and its eddies can directly impact the depth of isotherms, the isotherms are deepened underneath the Loop Current and anticyclones but uplifted on their inshore periphery. The Loop Current also interacts with the west Florida shelf and generates a high pressure gradient that extends northward along the continental slope into the study domain. Consequently, large-scale and persistent upwelling and downwelling events take place over the continental slope of the domain. The vertical excursions mostly range from ±35 to ± 50 m for the shallow isopycnals but can reach to over ± 100 m. Most distinct upwelling and downwelling events are short duration on the order of days, however there is a significant chance for persistent events, which can be induced by either remote or direct interaction of the Loop Current and/or eddies with the slope.
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Date Issued: 2014
Identifier: FSU_migr_etd-9222
Format: Thesis

Title: The Effects of Sea Surface Temperature Gradients on Surface Turbulent Fluxes.
Creator: Steffen, John, Bourassa, Mark A., Hart, Robert, Chagnon, Jeffrey, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: A positive correlation between sea surface temperature (SST) and wind stress perturbation near strong SST gradients (ΔSST) has been observed in different parts of the world ocean, such as the Gulf Stream in the North Atlantic and the Kuroshio Extension east of Japan. These changes in winds and SSTs can modify near–surface stability, surface stress, and latent and sensible heat fluxes. In general, these small scale processes are poorly modeled in Numerical Weather Prediction (NWP) and climate...
Show moreA positive correlation between sea surface temperature (SST) and wind stress perturbation near strong SST gradients (ΔSST) has been observed in different parts of the world ocean, such as the Gulf Stream in the North Atlantic and the Kuroshio Extension east of Japan. These changes in winds and SSTs can modify near–surface stability, surface stress, and latent and sensible heat fluxes. In general, these small scale processes are poorly modeled in Numerical Weather Prediction (NWP) and climate models. Failure to account for these air–sea interactions produces inaccurate values of turbulent fluxes, and therefore a misrepresentation of the energy, moisture, and momentum budgets. Our goal is to determine the change in these surface turbulent fluxes due to overlooking the correlated variability in winds, SSTs, and related variables. To model these air–sea interactions, a flux model was forced with and without SST–induced changes to the surface wind fields. The SST modification to the wind fields is based on a baroclinic argument as implemented by the University of Washington Planetary Boundary–Layer (UWPBL) model. Other input parameters include 2–m air temperature, 2–m dew point temperature, surface pressure (all from ERA–interim), and Reynolds Daily Optimum Interpolation Sea Surface Temperature (OISST). Flux model runs are performed every 6 hours starting in December 2002 and ending in November 2003. From these model outputs, seasonal, monthly, and daily means of the difference between ΔSST and no ΔSST effects on sensible heat flux (SHF), latent heat flux (LHF), and surface stress are calculated. Since the greatest impacts occur during the winter season, six additional December–January–February (DJF) seasons were analyzed for 1987—1990 and 1999—2002. The greatest differences in surface turbulent fluxes are concentrated near strong SST fronts associated with the Gulf Stream and Kuroshio Extension. On average, 2002—2003 DJF seasonal differences in SHF, LHF, and wind stress over the Gulf Stream are 3.86 ± 0.096 W/m2, 6.84 ± 0.186 W/m2, and 0.032 ± 0.0008 N/m2, respectively. In addition, smaller flux differences covering large expanses of the Atlantic and Pacific Oceans are non–negligible for most upper oceanic applications sensitive to multi–decadal changes. Due to these non–linear processes, average changes in surface turbulent fluxes are not zero.
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Date Issued: 2014
Identifier: FSU_migr_etd-9100
Format: Thesis

Title: Improving Forecasts of First Cloud-to-Ground Lightning Flashes Using Relationships Between Reflectivity and in-Cloud Flashes.
Creator: Lahr, Andrew D., Fuelberg, Henry, Misra, Vasubandhu, Ray, Peter, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Studies on the timing of cloud-to-ground (CG) lightning initiation have been conducted for various regions of the United States. There is evidence that in-cloud (IC) flashes often precede CG flashes by 10 or more minutes in the Great Plains. However, this difference in timing seems to decrease in more southern regions. This study analyzes the IC-CG timing issue within ~100 km of Kennedy Space Center, FL. We track 75 discrete single-cell thunderstorms within the KSC domain. Dual-polarimetric...
Show moreStudies on the timing of cloud-to-ground (CG) lightning initiation have been conducted for various regions of the United States. There is evidence that in-cloud (IC) flashes often precede CG flashes by 10 or more minutes in the Great Plains. However, this difference in timing seems to decrease in more southern regions. This study analyzes the IC-CG timing issue within ~100 km of Kennedy Space Center, FL. We track 75 discrete single-cell thunderstorms within the KSC domain. Dual-polarimetric radar data overlaid with lightning data are analyzed using the Warning Decision Support System - Integrated Information (WDSS-II) software. Statistics were gathered for three CG initiation scenarios: 1) the first in-cloud flash in the thunderstorm cell, 2) the first 35 dBZ reflectivity at the -10°C altitude, and 3) the first 40 dBZ at -10°C. Verification statistics such as probability of detection (POD) and false alarm ratio (FAR) were computed for each initiation approach. The first in-cloud flash approach produces small lead times (4.8 min) and relatively poor verification statistics, namely a CSI of 75%, a POD of 85%, and an FAR of 15%. The 4.8 min average time between the first IC and CG flashes appears too short to provide useful safety information. The 35 dBZ method provides the greatest lead time (mean of 14.5 min) and compared to the first in-cloud flash method, has a higher CSI (85%) and POD (99%), and a slightly lower FAR (14%). The 40 dBZ method has only marginally better statistics (88% CSI, 97% POD, and 9% FAR), but at the expense of 4 min of average lead time. These results suggest that the 35 dBZ threshold at -10°C is the most operationally applicable for forecasting the first CG flash in Florida.
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Date Issued: 2014
Identifier: FSU_migr_etd-9023
Format: Thesis

Title: Oligocene-Lower Miocene Calcareous Nannofossil Biostratigraphy of ODP Leg 154 Hole 929A from the Western Equatorial Atlantic at the Ceara Rise.
Creator: Sezen, Tugba, Wise, Sherwood W., Wang, Yang, Parker, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: ABSTRACT The Ocean Drilling Program (ODP) Leg 154 in the western equatorial Atlantic cored Paleocene - Holocene strata at Site 929 on the Ceara Rise. The calcareous nannofossil biostratigraphy of the Oligocene - lower Miocene sequence at Hole 929A is a necessary compliment to shipboard analysis. The analysis of Hole 929A samples presented here yielded 9 biozones defined by 10 nannofossil datums. Of these datums, two first occurrences (FO) and eight last occurrences (LO) were distinguished...
Show moreABSTRACT The Ocean Drilling Program (ODP) Leg 154 in the western equatorial Atlantic cored Paleocene - Holocene strata at Site 929 on the Ceara Rise. The calcareous nannofossil biostratigraphy of the Oligocene - lower Miocene sequence at Hole 929A is a necessary compliment to shipboard analysis. The analysis of Hole 929A samples presented here yielded 9 biozones defined by 10 nannofossil datums. Of these datums, two first occurrences (FO) and eight last occurrences (LO) were distinguished according to the Martini (1971) Zonation scheme. Based on quantitative analysis 21 genera and 79 species were identified in this section. The assemblages have abundances from rare to very abundant with moderate to good preservation and overgrowth on the lower Miocene discoasters. The Ceara Rise and the analogous Sierra Leone Rise are located on opposite sides of the equatorial Atlantic Ocean and are bounded by the same fracture zones. The Ceara Rise is on the western side, whereas the Sierra Leone Rise is in the eastern side. The two sites, Site 929 and Site 366, on these two rises were correlated via their nannofossils. However, because of poor preservation at Site 366 the zonal boundaries between NN3/NN2, NN1/ NP25, and NP22/NP21 are not well detailed. The relative abundance (%) of the total assemblages and their sedimentation rates in the western equatorial Atlantic were also calculated, and those for Hole 929A were generally higher.
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Date Issued: 2014
Identifier: FSU_migr_etd-9091
Format: Thesis

Title: Isotopic Characterization of Methane Obtained from Hypersaline Environments.
Creator: Tazaz, Amanda Maaza, Chanton, Jeffery, Mason, Patrick, Huettel, Marcus, Wang, Yang, Lapham, Laura, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The recent reports of methane in the atmosphere of Mars, as well as the findings of hypersaline paleoenvironments on that planet, have underscored the need to evaluate the importance of biological (as opposed to geological) trace gas production and consumption, particularly in hypersaline environments. Methane in the atmosphere of Mars may be an indication of extant life, but it may also be a consequence of geologic activity and/or the thermal alteration of ancient organic matter. On Earth...
Show moreThe recent reports of methane in the atmosphere of Mars, as well as the findings of hypersaline paleoenvironments on that planet, have underscored the need to evaluate the importance of biological (as opposed to geological) trace gas production and consumption, particularly in hypersaline environments. Methane in the atmosphere of Mars may be an indication of extant life, but it may also be a consequence of geologic activity and/or the thermal alteration of ancient organic matter. On Earth these methane sources can be distinguished using stable isotopic analyses and the ratio of methane (C1) to C2 and C3 alkanes present in the gas source (C1/(C2+C3)). We report here that methane produced in hypersaline environments on Earth has an isotopic composition and alkane content outside the values presently considered to indicate a biogenic origin. Higher salinity endoevaporites yielded what would be considered nonbiogenic methane based upon stable isotopic and alkane content, however incubation of crustal and algal mat samples resulted in methane production with similar isotopic values. Radiocarbon analysis indicated that the production of the methane was from recently fixed carbon. An extension of the isotopic boundaries of biogenic methane is necessary in order to avoid the possibility of false negatives returned from measurements of methane on Mars and other planetary bodies.
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Date Issued: 2013
Identifier: FSU_migr_etd-8719
Format: Thesis

Title: High-Resolution Calcareous Nannofossil Biostratigraphic Applications: Examples from the Upper Cretaceous Southern Ocean (ODP Leg 183) and Paleocene Equatorial Atlantic (ODP Leg 207).
Creator: Mitchell-Tapping, Aleta M., Wise, Sherwood W., Keller, Laura, Parker, William C., Wang, Yang, Burnett, William, Department of Earth, Ocean and Atmospheric Sciences, Florida...
Show moreMitchell-Tapping, Aleta M., Wise, Sherwood W., Keller, Laura, Parker, William C., Wang, Yang, Burnett, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: This dissertation is a collection of high-resolution calcareous nannofossil biostratigraphic projects. The projects are from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (Hole 1138A) and ODP Leg 207 to the Demerara Rise, off the coast of Suriname South America (Hole 1258A). These projects illustrate the important contribution of calcareous nannofossil biostratigraphy in understanding the paleoceanography of these regions. Chapter 2 details the results of a high-resolution...
Show moreThis dissertation is a collection of high-resolution calcareous nannofossil biostratigraphic projects. The projects are from Ocean Drilling Program (ODP) Leg 183 to the Kerguelen Plateau (Hole 1138A) and ODP Leg 207 to the Demerara Rise, off the coast of Suriname South America (Hole 1258A). These projects illustrate the important contribution of calcareous nannofossil biostratigraphy in understanding the paleoceanography of these regions. Chapter 2 details the results of a high-resolution biostratigraphic calcareous nannofossil study on Oceanic Anoxic Event 2 (OAE2) on the Kerguelen Plateau in the Southern Ocean. The distinct lack of calcareous nannofossils led to the delineation of OAE2 and suggests that anoxia had expanded to within the photic zone of the surface water column, indicating a collapse in the vertical stratification of these waters. A rise in sea level expanded this anoxia to shallower areas, whereby the leaching of nutrients led to fertilization and productivity in the ocean basin. In addition, the finding of a recurring post-anoxic event indicates that these oceanic conditions continued into the Turonian and signified changing sea surface temperatures and salinity levels that affected surface circulation patterns, unique to this basin. These findings are significant in identifying additional hydrocarbon deposits. Chapter 3 presents the results from another high-resolution calcareous nannofossil biostratigraphic study from the Kerguelen Plateau. This study delineates 16 bioevents spanning the Coniacian to Santonian. Five of these 16 bioevents have been previously discussed in the literature. Eleven new bioevents are identified in this study. The abundance of r-selected taxa in these samples suggests cool, eutrophic surface water conditions during this time. Chapters 4 and 5 examine calcareous nannofossils from lower Paleocene sediments of Hole 1258A on ODP Leg 207 to the Demerara Rise off Suriname, South America. An overall increasing trend in calcareous nannofossil diversity is consistent with other lower Paleocene studies. A warm-water environment is interpreted for the lower Paleocene, with cool-water incursions. This study examines the paleoecological response of calcareous nannofossils after a mass extinction event. From this same material, a new species is identified, Bomolithus lucidus, that is described in Chapter 5. Chapter 6 analyzes lower Paleocene sediment from Hole 1259B from ODP Leg 207 to delineate intervals in which Braarudosphaera taxa were found. The geographic restriction of the Braarudosphaera blooms to the Atlantic Ocean has been noted in numerous studies. It is proposed that parallel transform faults had enough vertical relief to act as a barrier and restrict circulation. The influx of nutrients and fresh water from the continent would also have supported an environment conducive to bloom events.
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Date Issued: 2013
Identifier: FSU_migr_etd-7932
Format: Thesis

Title: Dune and Shoreline Evolution of Western Santa Rosa Isand, Florida, 1973-2013.
Creator: Bambach, Philip W., Kish, Stephen A., Donoghue, Joseph F., Parker, William C., Wang, Yang, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The foredunes at twenty locations on Santa Rosa Island, Florida have been eroded to varying degree in response to Hurricanes Opal (1995), Ivan (2004) and Dennis (2005). At locations where pre-storm foredunes were high and the island was relatively wide, less coastal erosion occurred as a result of storm surge and high winds. For the western portions of Santa Rosa Island Hurricane Ivan had a greater effect on the volume of foredunes and backshore sand than did Hurricane Opal. More erosion is...
Show moreThe foredunes at twenty locations on Santa Rosa Island, Florida have been eroded to varying degree in response to Hurricanes Opal (1995), Ivan (2004) and Dennis (2005). At locations where pre-storm foredunes were high and the island was relatively wide, less coastal erosion occurred as a result of storm surge and high winds. For the western portions of Santa Rosa Island Hurricane Ivan had a greater effect on the volume of foredunes and backshore sand than did Hurricane Opal. More erosion is believed to have occurred during Hurricane Ivan because precursor erosion associated with Hurricane Opal, creating a more vulnerable setting for intense erosion during Hurricane Ivan. During calm conditions, foredunes accrete and migrate inland or prograde depending on shoreline position. In locations where a dune was not completely destroyed by storm surge from a hurricane event, the recovery rate was initially rapid, on the order of 1 ft of dune aggradation per year. In locations where the dunes were completely destroyed due to storm-surge, the recovery rate was much slower, on the order of 0.33 ft of dune aggradation per year. During the time period covered by this study (1973-2013), the foredunes migrated inland seemingly in step with the retreating shoreline. Santa Rosa Island experienced net volume loss of foredune and backshore sediment as well as a net shoreline retreat. Net volume loss of the foredunes and backshore was calculated at seventeen of the twenty locations where profiles were quantified. The greatest volume loss was approximately 58 ft3/ yr per lateral meter. The western portion of the island was the exception where net volume gain occurred at a rate of approximately 104 ft3/ yr per lateral meter. The shoreline retreated at varying degrees at all twenty locations. The most rapid shoreline retreat was approximately 8 ft/yr and the slowest rate was approximately 0.75ft/yr. During the 40-year time period covered in this study, central and western Santa Rosa Island experienced net shoreline retreat and a moderate net volume loss of sand on the backshore and foredunes, similar to results found in previous studies in the Northeast Gulf of Mexico. The retreat is associated with hurricane events that are followed by a limited recovery of the shoreline.
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Date Issued: 2013
Identifier: FSU_migr_etd-8526
Format: Thesis

Title: Stable Carbon and Oxygen Isotopes in Cetaceans and in Terrestrial Herbivores as Indicators of Diet, Movement and Environment: Paleoceanographic, Paleoclimatic and Paleoecologic Applications.
Creator: Ciner, Burcu, Wang, Yang, Erickson, Gregory M., Odom, Arthur L., Parker, William C., Kish, Stephen A., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Stable oxygen and carbon isotopic compositions of modern and fossil cetacean teeth and bones were analyzed to examine if and how they reflect the diet, habitat preference and migratory patterns of modern whales and to reconstruct the oxygen isotopic compositions of ancient ocean waters in the Mio-Pliocene. In addition, as a separate project, terrestrial mammal teeth and bone samples from Yushe Basin in North China were analyzed to examine long-term changes in diets and environments of mammals...
Show moreStable oxygen and carbon isotopic compositions of modern and fossil cetacean teeth and bones were analyzed to examine if and how they reflect the diet, habitat preference and migratory patterns of modern whales and to reconstruct the oxygen isotopic compositions of ancient ocean waters in the Mio-Pliocene. In addition, as a separate project, terrestrial mammal teeth and bone samples from Yushe Basin in North China were analyzed to examine long-term changes in diets and environments of mammals in the area over the past 6-7 million years to understand the development of C4 ecosystems in North China and the effects of Tibetan uplift on regional climate and ecosystems. The major results are as follows: (1) The oxygen isotopic compositions of phosphate (δ18Op) in teeth and bones from 5 different modern cetacean species including sperm whale, pygmy sperm whale, short-finned pilot whale, killer whale and Cuvier's beaked whale were analyzed. The δ18Op values range from 16.7 / to 21.3 /, averaging 19.6±1.0 / (n=89), for tooth samples, and from 15.5 / to 19.7 /, with an average of 19.0±0.9 / (n=47), for ear bone samples. The new δ18Op data, along with data compiled from literature, were used in conjunction with modern ocean δ18Osw data to examine the relationships between δ18Op and δ18Osw, yielding the following equations: Teeth: δ18Op= 19.173 + 0.9296 δ18Osw R2 = 0.8723 Bones: δ18Op = 18.109 + 0.8436 δ18Osw R2 = 0.86 The new equations, when applied to fossil teeth and bones yielded more reasonable estimates of ancient ocean water δ18O values than the original equation given in Yoshida and Miyazaki (1991). Intra-tooth isotopic variations were observed within individual teeth. Among the selected species, the killer whale (O. orca) displayed the most depleted δ18Op values (~18 /) and the largest intra-tooth δ18O variation (2.8 /), reflecting its habitat preference and migratory behavior. (2) Stable carbon and oxygen isotopic compositions of teeth and ear bones from 19 modern whales representing 4 different toothed whale species of the sperm whale, pygmy sperm whale, short-finned pilot whale and killer whale were analyzed. While tooth-δ13C values range from -8.2 / to -12.7 /, averaging -10.5±1.2 / (n=87), ear bone δ13C values range from -9.9 / to -11.8 /, averaging -10.7±0.6 / (n=19). The δ13C and δ18O values are generally consistent with their known diets and habitats. Synchronous positive shifts in the δ13C chronological profiles of all teeth from short-finned pilot whales (G. macrorhynchus) from Florida might indicate a shift in diet and/or habitat from coastal areas to offshore areas and feeding on relatively high δ13C preys. Structural carbonate in bioapatite appears to be enriched in δ13>C by ~3 / relative to collagen and by ~8 / relative to muscles. This suggests a carbon isotopic offset of ~9 / due to biochemical fractionation between structural carbonate in bioapatite and the diet. The δ13C data reveal that the diet-δ13C values of killer whales were about -20 - -21 /, consistent with a fish-based diet. The diet-δ13C values of the sperm whale, short-finned pilot whale and pygmy sperm whale were ~ -18- -19 /, in agreement with a diet consisting of both cephalopod and fish. (3) Stable carbon and oxygen isotope ratios of 310 enamel samples from a diverse group of herbivorous mammals including Equidae, Rhinocerotidae, Bovidae, Rodentia and Ochotonidae from Yushe Basin, North China were analyzed. The δ13C values of bulk and serial enamel samples from large mammals show a wide range of variation from –13.3 / to 1.4 /, with a mean of -7.4 / +3.5 / (n=294). This indicates that large herbivorous mammals in the area had a variety of diets since 6.5 Ma, ranging from pure C3 to mixed C3-C4 and pure C4 diets. In contrast, the δ13C values of small mammals from Rodentia and Ochotonidae families vary from –11.9 / to -7.6 /, with a mean of -9.7±1.1 / (n=16), indicating that theses small mammals were feeding predominantly on C3 plants. The carbon isotope data show that C4 grasses have been an important component of horses' diets and of local ecosystems since ~6.5 Ma, confirming that the "late Miocene C4 expansion" occurred in North China as it did in Africa, Indian subcontinent and the Americas. This supports a global factor as a main driver of the late Miocene C4 expansion. The combined carbon and oxygen isotope data reveal major shifts in climate to drier and/or warmer conditions after ~5.8, ~4.1, ~3.3, and ~2.5 Ma, and significant shifts to relatively wetter and/or cooler conditions after ~6.4, ~5, ~3.5 Ma. The shifts to drier and/or warmer climate after ~5.8 Ma and ~2.5 Ma coincide with two major fauna turnover events. Intra-tooth δ13C and δ18O values are negatively correlated within individual modern teeth and some fossil teeth, displaying the characteristic pattern of the summer monsoon regime and confirming the strong monsoon influence in the area since at least the early Pliocene. The data also suggest that the C4 abundance in the area has fluctuated over the past 6.5 Ma in response to changes in climate, with more C4 grasses during warmer and/or drier periods and a reduced C4 biomass at cooler and/or wetter times.
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Date Issued: 2013
Identifier: FSU_migr_etd-8696
Format: Thesis

Title: Geostatistical Analysis of Sinkhole Occurrence Due to Increased Groundwater Pumping during Freeze Events in Plant City, Florida.
Creator: White, Corie L., Parker, William C., Kish, Stephen, Ye, Ming, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Located in West Central Florida, Plant City is an agriculturally dominated region, growing strawberries and citrus. Due to temperatures during winter months, when they often fall below freezing, farmers in the area must use freeze protection techniques to protect their crops. The method of choice is pump-irrigation in which farmers pump large quantities of warm groundwater from subsurface aquifers and apply it directly to the crops. The water forms a protective layer of ice that prevents the...
Show moreLocated in West Central Florida, Plant City is an agriculturally dominated region, growing strawberries and citrus. Due to temperatures during winter months, when they often fall below freezing, farmers in the area must use freeze protection techniques to protect their crops. The method of choice is pump-irrigation in which farmers pump large quantities of warm groundwater from subsurface aquifers and apply it directly to the crops. The water forms a protective layer of ice that prevents the crops from spoiling during the cold spells. The extraction of vast amounts of groundwater correlates with cover-collapse sinkholes. This is due mainly to the underlying limestone platform of Florida and also to loss of buoyant support. Previous freeze events have occurred in January of 1977, 1985, and 2010. The event of January 2010 was by far the most catastrophic; the freeze lasted eleven days and caused over 140 sinkholes. By examining water level data from monitoring wells in the area, sinkhole reports, and overburden thickness for the events of January 1985 and January 2010, this research examines the relationships between groundwater withdrawl during freeze events and sinkholes through geostatistics. Results show that amount of drawdown is the main factor in predicting sinkholes.
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Date Issued: 2013
Identifier: FSU_migr_etd-7659
Format: Thesis

Title: Circulation Dynamics and Larval Transport Mechanisms in the Florida Big Bend.
Creator: Todd, Austin C., Chassignet, Eric, Bourassa, Mark, Clarke, Allan, Coleman, Felicia, Dewar, William, Heuttel, Markus, Morey, Steven, Department of Earth, Ocean and Atmospheric...
Show moreTodd, Austin C., Chassignet, Eric, Bourassa, Mark, Clarke, Allan, Coleman, Felicia, Dewar, William, Heuttel, Markus, Morey, Steven, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: The Florida Big Bend region in the northeastern Gulf of Mexico contains both spawning sites and nursery habitats for a variety of economically valuable marine species. One species, the gag grouper (Mycteroperca microlepis), relies on the shelf circulation to distribute larvae from shelf-break spawning grounds to coastal seagrass nurseries each spring. Therefore, identifying the dominant circulation features and physical mechanisms that contribute to cross-shore transport during the springtime...
Show moreThe Florida Big Bend region in the northeastern Gulf of Mexico contains both spawning sites and nursery habitats for a variety of economically valuable marine species. One species, the gag grouper (Mycteroperca microlepis), relies on the shelf circulation to distribute larvae from shelf-break spawning grounds to coastal seagrass nurseries each spring. Therefore, identifying the dominant circulation features and physical mechanisms that contribute to cross-shore transport during the springtime may provide valuable insight into the variation of the abundance of this reef fish. The physical mechanisms by which cross-shelf movement is possible, and the pathways by which materials may be transported onshore are examined. More specifically, variable wind stress and the conservation of potential vorticity are investigated for their role in setting the net across-shelf transport, using a very high horizontal resolution (800—900 m) numerical ocean model. The simulations demonstrate that the mean springtime shelf circulation is set by the rectification of flow during northwesterly or southeasterly directed wind stress, and significant cross-shelf flow may be generated during winds from the northwest. The springtime flow is mostly barotropic and tends to conserve potential vorticity over time scales shorter than about 12 hrs. For longer time scales, the nonconservation of potential vorticity enables movement of particles inshore. Particle advection experiments demonstrate that a primary pathway exists south of St. George Island by which particles are able to reach the nearshore environment, and that preferred release locations for particles to successfully arrive inshore coincide with known gag spawning aggregation sites. The results provide, for the first time, a description of the mechanisms by which onshore transport is possible from gag spawning sites at the shelf break to seagrass nurseries at the coast.
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Date Issued: 2013
Identifier: FSU_migr_etd-7630
Format: Thesis

Title: Manatee Behavioral Response to Approaching Boats.
Creator: Rycyk, Athena, Dewar, William, Blessing, Susan, Nowacek, Douglas, Chanton, Jeffrey, Deutsch, Charles, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: The Florida manatee (Trichechus manatus latirostris) inhabits coastal and inland waters in the southeastern United States, and its long-term survival is threatened in part by mortality from boat collisions. This study investigated manatee behavior during boat approaches to better understand the factors that lead to boat-manatee collisions. Digital acoustic recording tags (DTAGs) and satellite-linked GPS tags were deployed on 18 Florida manatees in southwest Florida, and the boat traffic...
Show moreThe Florida manatee (Trichechus manatus latirostris) inhabits coastal and inland waters in the southeastern United States, and its long-term survival is threatened in part by mortality from boat collisions. This study investigated manatee behavior during boat approaches to better understand the factors that lead to boat-manatee collisions. Digital acoustic recording tags (DTAGs) and satellite-linked GPS tags were deployed on 18 Florida manatees in southwest Florida, and the boat traffic around them was mapped. Suites of manatee behavioral, environmental, boat-related, and acoustic variables were measured during opportunistic boat passes. A subset of these variables was used to create and compare numerous models to predict the occurrence, magnitude, and timing of manatee changes in behavior during boat passes. Model averaging techniques were used to discern the relative importance of each variable. Some models accounted for a relatively high proportion of variance in the occurrence (up to R2 of 0.55), magnitude (up to R2 of 0.58), and timing (up to of R2 of 0.75) of changes in manatee behavior during boat passes. Manatees clearly responded to boats: they changed their orientation (heading, roll), depth, and fluking behavior significantly more often when a boat approached closely (within 50 m) than in the absence of boats. Boats traveling at slow speeds elicited changes in behavior that were more likely to occur before the boat's closest point of approach (CPA) compared to boats traveling on a plane. These findings concur with previous evaluations that slower boats allow the manatee more time to respond; coupled with the higher risk of mortality from collisions with faster moving boats, the evidence indicates that slower boats reduce the risk of manatee mortality. Manatee activity before boat approaches was an important factor affecting probability of behavioral change during boat passes. Manatees engaged in a high fluking state (e.g., as occurs during traveling) before boat approaches were more likely to change behavior and to do so sooner (relative to the start of a boat pass) than manatees in a lower fluking state (e.g., as occurs during resting). Manatees suspected to be feeding were more likely to change heading during boat passes. Manatees spent a large proportion of time on seagrass beds, where they were less likely to change depth in response to an approaching boat. It is possible that on a seagrass bed 1) a manatee's options are limited by water depth, 2) they are more motivated to continue their current activity than to respond to a boat, 3) they are in a lower activity state and therefore less likely to change their depth, or 4) manatees cannot detect approaching boats as easily on seagrass beds because background noise is louder and transmission loss is higher. Water depth was another important feature of the habitat that influenced a manatee's response to an approaching boat. Manatees in deeper water were more likely to change fluking behavior, and their changes in depth were of larger magnitude. A manatee is more vulnerable to a boat strike while near the surface; here, manatees closer to the surface were more likely to change their behavior and with less of a time delay (relative to the start of the pass and to CPA) than manatees deeper in the water column. The acoustic properties of boat noise were important, such that louder boats were more likely to elicit a change in a behavior. Sound level, however, did not affect the magnitude or timing of changes in behavior. The rate of change in sound level before CPA was linked to the timing of behavioral changes, with steep rises in sound level associated with a shorter time delay (after the start of the pass) for the first change in behavior. The evaluation of behavioral response of tagged manatees was conducted in southwest Florida, where boat traffic is relatively high. These data were compared to that of an individual manatee in Belize, where manatees (Trichechus manatus manatus) are exposed to far less boat traffic, from a previous study that also deployed DTAGs. Although the small sample size precludes any firm conclusions, differences between the responses were striking. The Belize manatee responded to approaching boats far earlier than manatees in Florida and exhibited a sudden change in behavior, called a `jerk', in two of four passes. As a whole, this study evaluated the type and range of manatee behavioral responses to approaching boats, and identified several factors that appear to influence this response. For instance, the probability of behavior changes was linked to manatee behavior prior to a boat pass and local environmental factors such as seagrass coverage and water depth, and the speed of the boat affected the timing of these changes. Both the probability and timing of behavioral changes were influenced by other acoustic properties of boat noise, such as sound level and its rise rate. In future work, controlled approaches that maintain the high-sensitivity of DTAG-based detection of behavioral changes may be a promising approach to test specific aspects of these results, and further elucidate the environmental and behavioral factors useful for improving current management strategies to minimize boat-related manatee mortality.
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Date Issued: 2013
Identifier: FSU_migr_etd-7589
Format: Thesis

Title: Radon Solubility in Water as a Function of Salinity and Temperature.
Creator: Lieberman, Eric B., Burnett, William, Humayun, Munir, Cooper, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Radon is an important natural tracer for certain aquatic environmental studies. New methods for rapidly determining submarine groundwater discharge (SGD) into surface waters in the coastal zone rely on the accuracy of the air/water partitioning coefficient for doing radon mapping of coastal waters. The original research that determined the radon partitioning coefficient was conducted in 1916 and more recent published analysis of these data only accounted for temperature changes in fresh water...
Show moreRadon is an important natural tracer for certain aquatic environmental studies. New methods for rapidly determining submarine groundwater discharge (SGD) into surface waters in the coastal zone rely on the accuracy of the air/water partitioning coefficient for doing radon mapping of coastal waters. The original research that determined the radon partitioning coefficient was conducted in 1916 and more recent published analysis of these data only accounted for temperature changes in fresh water. My research was designed to: 1) determine the partition coefficient by accurately measuring the gas and water phase concentrations of 222Rn when the radon is in equilibrium between both phases; 2) minimize the error due to multiple analytical system calibrations; and 3) calculate the partition coefficient at different temperatures and salinities. I focused on 2 different experimental setups, one designed to directly measure the radon concentration of the gas phase and the dissolved concentration in the liquid phase (known as the direct measurement or volume independent method), and the other was hoped to be a rapid measurement system that only required a continuous measurement of the gas phase to determine the partitioning coefficient at different temperatures (the indirect measurement or volume dependent method). I combined my research results with parallel research experiments being conducted in Leipzig, Germany and together we redefined the air/water partitioning coefficient of radon gas with respect to both salinity and temperature. By analyzing our combined results, we developed a new set parameters a1 - b3 for use in the Weiss Equation, which could then be used to determine the partitioning coefficient of radon at different salinities and temperatures. Our results showed that if salinity effects are neglected in warm, relatively low salinity waters (e.g., coastal waters from the Gulf of Mexico), there was a slight overestimation of the radon concentration (up to 10%), but in colder, higher salinity waters, this overestimation could exceed 20%.
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Date Issued: 2013
Identifier: FSU_migr_etd-7468
Format: Thesis

Title: Pleistocene Calcareous Nannofossil Biostratigraphy of Site U1352, Canterbury Basin, New Zealand.
Creator: Myers, Nicholas R., Wise, Sherwood W., Parker, William, Wang, Yang, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: During IODP Leg 317 off the east coast of New Zealand, three continental shelf sites (U1351, U1353 and U1354) and one continental slope site were cored. Sedimentary sequences representing shallow water depositional cycles were recovered and ranged from Upper Miocene to recent in age. One of the most widely used tools in the academic and scientific realm by onboard paleontologists to quickly determine such ages, along with foraminifera, are calcareous nannofossils. Adequate ages are highly...
Show moreDuring IODP Leg 317 off the east coast of New Zealand, three continental shelf sites (U1351, U1353 and U1354) and one continental slope site were cored. Sedimentary sequences representing shallow water depositional cycles were recovered and ranged from Upper Miocene to recent in age. One of the most widely used tools in the academic and scientific realm by onboard paleontologists to quickly determine such ages, along with foraminifera, are calcareous nannofossils. Adequate ages are highly dependent on the amount of time the shipboard paleontologist has to scan samples for biozone markers, and in some instances, zonal markers are unable to be found. Therefore, it is sometimes necessary for a secondary, post-cruise analysis of sediments to confirm the biostratigraphy developed during the cruise. Secondary objectives for this project include development of calcareous nannofossil abundance counts to analyze population dynamics, richness, evenness, and diversity as well as examination of ages and abundances of reworked and transported nannofossil assemblages in order to better understand transport mechanisms and sediment sourcing of the area. This additional onshore post-cruise analysis will allow for a more detailed study of the biozonation of the region as well as general assemblages. It is also believed that nannofossil abundances/assemblages undergo a profound change across sequence stratigraphic boundaries. This work aims to analyze these changes and determine the feasibility of using nannofossils to study these depositional cycles. Simple smear-slides have been prepared from ~100 samples and are currently undergoing semi-quantitative analysis using an Axioscope II light microscope. Shipboard biostratigraphic analysis of calcareous nannoplankton is crucial for accurate determination of stratigraphic ages due to their diversity, rapid evolution/mutation, and abundance in marine sediments. Establishing good age control allows for correlation with other proxies to develop precise chronology of cored sediments.
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Date Issued: 2013
Identifier: FSU_migr_etd-7523
Format: Thesis

Title: Physical Description and Analysis of the Variability of Salinity and Oxygen in Apalachicola Bay.
Creator: Mortenson, Eric, Speer, Kevin, Chicken, Eric, Dewar, William, Bourassa, Mark, Landing, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Apalachicola Bay is a shallow estuarine system enclosed by a chain of barrier islands on the west Florida shelf. It is important both ecologically and economically due to the high biological productivity in the bay. The bay is subject to fluctuations in salinity, temperature, and dissolved oxygen. Salinity fluctuations are beneficial to many organisms in the bay. Measurements in and around the bay are analyzed to give a general description of how the bay's hydrographic properties vary in...
Show moreApalachicola Bay is a shallow estuarine system enclosed by a chain of barrier islands on the west Florida shelf. It is important both ecologically and economically due to the high biological productivity in the bay. The bay is subject to fluctuations in salinity, temperature, and dissolved oxygen. Salinity fluctuations are beneficial to many organisms in the bay. Measurements in and around the bay are analyzed to give a general description of how the bay's hydrographic properties vary in space and time. A salinity model using conservation of mass and salt is constructed in order to describe how the bay's salinity changes due to various forcing mechanisms. The main factors affecting salinity in Apalachicola Bay are freshwater inflow from Apalachicola River, winds in the direction of the major axis of the bay, and to a lesser extent, tides. When smoothed with a ten day filter, the salt model results over the three year study period agree with observations in each side of the bay at a correlation between 0.8 and 0.9. Variations in the concentration of dissolved oxygen with time are also analyzed, and the processes driving these are wind speed, temperature, biological activity, and advection. During one period when tides affect the concentration of dissolved oxygen, a regressive model based on tidal velocity and light measured near the bottom agree with observation at a correlation of > 0.8.
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Date Issued: 2013
Identifier: FSU_migr_etd-7519
Format: Thesis

Title: Dealiasing Doppler Velocites Using Edge Detection.
Creator: Meech, Scott P., Ray, Peter, Fuelberg, Henry, Liu, Guosheng, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study presents a new algorithm to dealias folded Doppler velocities in S, C, and X-Band radars using a new boundary detection technique on the raw velocity field as a whole, rather than the traditional gate by gate methodology used in more popular and widespread algorithms. Several different types of precipitation events are used to compare and contrast the final output of the new boundary based algorithm. The results are then compared to the NEXRAD dealiasing algorithm as defined by...
Show moreThis study presents a new algorithm to dealias folded Doppler velocities in S, C, and X-Band radars using a new boundary detection technique on the raw velocity field as a whole, rather than the traditional gate by gate methodology used in more popular and widespread algorithms. Several different types of precipitation events are used to compare and contrast the final output of the new boundary based algorithm. The results are then compared to the NEXRAD dealiasing algorithm as defined by Eilts and Smith (1989) and an objective manual unfolding by radar manipulation software called SoloII.
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Date Issued: 2013
Identifier: FSU_migr_etd-7505
Format: Thesis

Title: Pliocene-Pleistocene Calcareous Nannofossil Biostratigraphy of IODP Hole 1396C Adjacent to Montserrat Island in the Lesser Antilles, Caribbean Sea, Plus Experimentally Induced Diagenesis.
Creator: Aljahdali, Mohammed H., Wise, Sherwood W., Wang, Yang, Parker, William, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Integrated Ocean Drilling Program Hole 1396C, adjacent to Montserrat Island, provides a lower Pliocene to Pleistocene record of calcareous nannofossil assemblages (CN11 to CN15). The nannofossil assemblages are generally common to abundant with moderate preservation in the upper Pleistocene, and very abundant with good preservation in the lower Pleistocene and the Pliocene. The sequence was zoned via the Gartner (1977) scheme for the Pleistocene and the Okada and Bukry (1980) zonation for the...
Show moreIntegrated Ocean Drilling Program Hole 1396C, adjacent to Montserrat Island, provides a lower Pliocene to Pleistocene record of calcareous nannofossil assemblages (CN11 to CN15). The nannofossil assemblages are generally common to abundant with moderate preservation in the upper Pleistocene, and very abundant with good preservation in the lower Pleistocene and the Pliocene. The sequence was zoned via the Gartner (1977) scheme for the Pleistocene and the Okada and Bukry (1980) zonation for the Pliocene using the recent age updates from Backman et al. (2012). Sedimentation rates inferred by nannofossil biostratigraphy suggest low sedimentation rates in the Pleistocene and high sedimentation rates during the Pliocene. This sedimentation pattern was also observed at Site 1000 from Ocean Drilling Program Leg 165 in the central Caribbean Sea, suggesting a regional event caused by the closure of the Central American seaway. During the expedition (IODP, Expedition 340), selected samples from Holes 1396A and C were used to determine the sediment water content by heating them at 105°C at room pressure for 24 hours. This process produced an artificial "late diagenesis" effect with severe overgrowth features on the nannofossils. Further examination of the diagenetic progression in these samples should provide a better understanding of the progression of carbonate diagenesis in cases of high temperatures and pressures.
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Date Issued: 2013
Identifier: FSU_migr_etd-7270
Format: Thesis

Title: Influence of Sedimentary Gas Ebullition on Interfacial Transport in Permeable Marine Sands.
Creator: Cheng, Chiu, Huettel, Markus, MacDonald, Ian, Kostka, Joel, Chanton, Jeffrey, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: In the uppermost millimeters of shallow marine sands, photosynthesis by microalgae can cause oxygen supersaturation, leading to formation of oxygen bubbles and subsequent ebullition of the gas from the sediment. The role of ebullition for transport and reaction mechanisms in sandy environments is poorly understood. I show that the ebullition of this gas from permeable sediments can affect the circulation and exchange of water across the sediment-water interface, thereby enhancing interfacial...
Show moreIn the uppermost millimeters of shallow marine sands, photosynthesis by microalgae can cause oxygen supersaturation, leading to formation of oxygen bubbles and subsequent ebullition of the gas from the sediment. The role of ebullition for transport and reaction mechanisms in sandy environments is poorly understood. I show that the ebullition of this gas from permeable sediments can affect the circulation and exchange of water across the sediment-water interface, thereby enhancing interfacial solute exchange. In sands, free gas occurs mostly as small inconspicuous interstitial bubbles in the surface layers that, despite their small size, can affect the physical characteristics of the sediment or surface because they are compressible and provide gas reservoirs that allow gas exchange. Over time, the gas will equilibrate with the surrounding environment, leading to a change in volume and composition. These processes may also affect the biogeochemical activities in the sediment and water column. The small bubbles in the interstitial spaces of sands can combine into bubbles in the millimeter size range with buoyancy large enough to penetrate the sediment resulting in ebullition. So far, this process of gas ebullition from permeable sand has not been investigated in detail. The main goal of this study was therefore, to assess the role of ebullition on solute flux and oxygen dynamics in the sediment. I conducted seasonal field measurements of gas ebullition and sediment free gas content, and analyzed the composition of these gases. The highest gas ebullition volumes were generally observed in the afternoon and evening hours before midnight, a pattern reflecting the build-up of oxygen in the sediment after sunrise, reaching supersaturation in the late morning hours and bubble formation thereafter. The lowest bubble volumes were measured after midnight and in the early morning. Ebullition rates reached up to a maximum 15.6 ml m-2 h-1 with a peak of 62.3 ml m-2 h 1 between the hours of 12:00-18:00 during the summer season. On a yearly average, about 59 ± 32 percent of the gas that was measured from the bay was released from the sediment. There is a noticeable offset between bubble formation in the sediment to maximum rates of gas release. The latter became most significant and exceeded the sedimentary gas volumes mainly during the afternoon hours. The maximum volume of gas was recorded in August at 492.4 ml m-2 d-1, which integrates gas volume released from the sediment and the free gas still present in the sediment. Assuming photosynthetic activity by microalgae only occurs down to a sediment depth of 0.5 cm, this gas volume theoretically equates to approximately 10% of the total sediment volume affected by gas bubble formation. In this study, most of the measured gas was not collected in the sediment, but rather in the overlying water column. The maximum volume of gas that a given volume of sediment can contain before ebullition occurs, at 1 cm sediment depth, was determined to be around 0.064 ± 0.005 ml in the lab. In the natural environment, this maximum volume would also largely depend on a variety of physical, chemical and biological factors. In order to assess the effect of ebullition on sediment-water solute exchange, I conducted laboratory experiments utilizing sediment columns with pore water that contained inert fluorescein dye. Bubbles released at six different depths in the sediment resulted in a 4 to 21 fold enhancement of sediment-water solute flux relative to diffusion-only transport. The strongest increase of dye flux from the pore water into the overlying water was recorded when bubbles were released closest to the sediment-water interface, where individual gas bubbles were the smallest in volume but the release rate of individual bubbles was the highest. Subsequent analyses of larger sediment cores (57 cm diameter, ~ 5 cm in height) revealed a distinct pattern of dye washout caused by the ebullition that extended below the level at which the gas was released at 2.5 cm depth. This result demonstrated the effectiveness of pore water circulation caused by bubble release for the vertical and horizontal mixing of pore fluids, particularly near the origin of ebullition. With a transfer of the laboratory experimental design to the field using 19-cm diameter chambers with rotating discs and chamber water spiked with inert bromide (Br-) tracer, we could show that the average volume of pore water exchange in five different ebullition chambers was 231 ± 96 L m-2 d-1. Compared to the average from four non-ebullition chambers (79 ± 96 L m-2 d-1), the difference in interfacial tracer flux caused by ebullition was almost 3-fold. Investigations were also undertaken on oxygen gas bubble behavior in both the field and laboratory. Correlation comparisons between the collected gas samples from St. Joseph Bay and the measured environmental factors show that the change in the gas volume is most closely associated with sunlight, albeit with a lag time. While the rate of increase in the oxygen concentration was the greatest at the onset of the day (6:00-12:00), the volume maxima was not typically reached until the afternoon hours. The average concentration of oxygen in the bubbles during the summer at the bay exceeded 50% in both the sediment and bubble trap samples. The flux of oxygen from the sediment through ebullition was up to 5.93 ± 0.63 mmol m-2 d-1 during August. Pure oxygen gas was released at the sediment-water interface, as well as 2 cm in the sediment and collected at 20-cm intervals up to 1 m to see if any immediate changes in composition would occur. The gas stripping was further pursued in the lab by injected known volumes of pure oxygen (5, 10 or 15 ml) into seawater control vials and (5 or 10 ml) into glass containers filled with fresh, wet sediment collected from the bay. The loss of oxygen in the rising bubbles in the water column at St. Joseph Bay was 21% greater when gas was injected at 2 cm in the sediment versus at the sediment surface. In the lab experiments the gas samples in the sediment loss 43 and 33 percent more oxygen following 24 hours, with rates of decrease approximately 4.9 and 5.5 times (5 and 10 ml experiments) higher than the controls. In all experiments, the sediment demonstrated higher rates of oxygen consumption than in the water column, and N2 was the only other gas found in all of our gas samples.
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Date Issued: 2013
Identifier: FSU_migr_etd-7329
Format: Thesis

Title: Atmospheric Power-Law Behavior: A Look into Southeastern US Daily Temperature Extremes.
Creator: Duncan, James Bean, Sura, Philip, Wu, Zhaohua, Bourassa, Mark, Stefanova, Lydia, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: Extreme events are phenomena which occupy the tail-end of a distributions PDF. While atmospheric phenomena are decidedly non-Gaussian, the exact shape of these tails of a distribution are relatively unknown. From stochastic theory, it is noted that tails or extremes may be predicted by the behavior of power-law distribution. While prior research for the empirical search for power-laws has been heavily qualitative in nature, this study aims at the quantitative and statistical fitting and...
Show moreExtreme events are phenomena which occupy the tail-end of a distributions PDF. While atmospheric phenomena are decidedly non-Gaussian, the exact shape of these tails of a distribution are relatively unknown. From stochastic theory, it is noted that tails or extremes may be predicted by the behavior of power-law distribution. While prior research for the empirical search for power-laws has been heavily qualitative in nature, this study aims at the quantitative and statistical fitting and analysis of power-laws across the southeastern United States with respect to daily maximum and minimum temperatures. Utilizing a power-law fitting algorithm, we may fit power-law distributions to the PDFs of atmospheric maximum and minimum temperatures. After statistical analysis, we may note the universal significance of these power-law tails throughout the southeastern United States within regions of non-Gaussianity. Further, we analyze varying behavior of these significant power-laws within the distribution's PDF. From this, we may note and observe the behavior of these extremes events in relation to weather and climatic cycles.
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Date Issued: 2013
Identifier: FSU_migr_etd-7362
Format: Thesis

Title: Assimilation of Lightning Data Using a Nudging Method Involving Low-Level Warming.
Creator: Marchand, Max R., Fuelberg, Henry, Ahlquist, Jon, Hart, Robert, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study presents a new method for assimilating lightning data into numerical models that is suitable for cloud-resolving scales (e.g., 3 km). The study utilized data from the Earth Networks Total Lightning Network at 9 km grid spacing to mimic the resolution of the Geostationary Lightning Mapper (GLM) that will be on the upcoming GOES-R satellites. The assimilation procedure was developed using the Weather Research and Forecasting (WRF) numerical model. The method (denoted MU) warms the...
Show moreThis study presents a new method for assimilating lightning data into numerical models that is suitable for cloud-resolving scales (e.g., 3 km). The study utilized data from the Earth Networks Total Lightning Network at 9 km grid spacing to mimic the resolution of the Geostationary Lightning Mapper (GLM) that will be on the upcoming GOES-R satellites. The assimilation procedure was developed using the Weather Research and Forecasting (WRF) numerical model. The method (denoted MU) warms the most unstable low levels of the atmosphere at locations where lightning was observed but deep convection was not simulated based on the absence of graupel. Simulation results utilizing the new method are compared with a control simulation and a simulation employing the lightning assimilation method (FO) developed by Alexandre Fierro and colleagues. Unlike MU, the FO method increases relative humidity according to a nudging function dependent on the intensity of observed lightning and simulated graupel mixing ratio. Simulations are performed across the Central and Eastern United States for three separate severe storm cases during 2011. These cases exhibit a wide range of weather patterns and thunderstorm organization. When comparing simulation results with hourly NCEP stage IV radar and gauge precipitation observations, both the MU and FO assimilation methods produce an improved simulated precipitation field during the assimilation period and a short time afterwards based on subjective comparison and objective statistical scores. The assimilation methods commonly improve equitable threat scores by more than 0.1 and 50% during the assimilation period. Differing degrees of improvement from the assimilation methods depend on the weather pattern, with the MU method generally performing better in the simulation of isolated thunderstorms and other weakly forced deep convection. Biases in the precipitation, moisture, and temperature fields of the simulations also are examined and sometimes differ considerably between assimilation schemes. Based on performance and bias, the newly developed MU method is shown to be a viable alternative to the FO method, exhibiting utility in producing and locating thunderstorms where observed and providing a better analysis at low computational cost.
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Date Issued: 2013
Identifier: FSU_migr_etd-7490
Format: Thesis

Title: FengYun-3B Microwave Humidity Sounder (MWHS) Data Noise Characterization and Filtering Using Principle Component Analysis.
Creator: Ma, Yuan, Zou, Xiaolei, Liu, Guosheng, Ray, Peter S., Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: MicroWave Humidity Sounder (MWHS) onboard both FY-3A and FY-3B satellites have three channels (channels 3-5) near 183 GHz water vapor absorption line. These channel frequencies are also used in other instruments such as Advanced Microwave Sounding Unit-B (AMSU-B) and Microwave Humidity Sounder (MHS) onboard MetOp and NOAA satellites. Both MWHS and MHS are cross-track scanners. In this study a comparison between the simulated brightness temperatures with MWHS measurements clearly shows that...
Show moreMicroWave Humidity Sounder (MWHS) onboard both FY-3A and FY-3B satellites have three channels (channels 3-5) near 183 GHz water vapor absorption line. These channel frequencies are also used in other instruments such as Advanced Microwave Sounding Unit-B (AMSU-B) and Microwave Humidity Sounder (MHS) onboard MetOp and NOAA satellites. Both MWHS and MHS are cross-track scanners. In this study a comparison between the simulated brightness temperatures with MWHS measurements clearly shows that MWHS observations from the three sounding channels contain a scan angle dependent cohesive noise along the instrument scanline. This noise does not cancel out when a large amount of data over a sufficiently long period of time is averaged, which eliminates the possibility of such a noise to arise from natural variability of the atmosphere and the surface. The noises are around 0.3, 0.2, and 0.2 K for channels 3-5, respectively. A principle component analysis is used for the characterization of this cohesive noise using one-month FY-3B MWHS data. It is shown that the MWHS cohesive noise is contained primarily in the first PC mode, which mainly describes a scan angle dependent brightness temperature variation, i.e., a unique feature of cross-tracking instrument. The 1st PC accounts for more than 99.91% total variance in the three MWHS sounding channels. A five-point smoother is then applied to the first PC, which effectively removes such a data noise in MWHS data. The reconstruction of the MWHS radiance spectra using the noise-filtered first PC component is of good quality. The scan angle dependent bias from reconstructed MWHS data becomes more uniform and is consistent with NOAA-18 MHS data.
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Date Issued: 2013
Identifier: FSU_migr_etd-7480
Format: Thesis

Title: Investigation of the Relationship Between the Yucatan Channel Transport and the Loop Current Area in a Multi-Decadal Numerical Simulation.
Creator: Nedbor-Gross, Robert, Bourassa, Mark A., Dukhovskoy, Dmitry S., Morey, Steven L., Chassignet, Eric P., Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida...
Show moreNedbor-Gross, Robert, Bourassa, Mark A., Dukhovskoy, Dmitry S., Morey, Steven L., Chassignet, Eric P., Sura, Philip, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
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Abstract/Description: A hypothesis by Maul [1977], stating the rate of change of Loop Current (LC) volume is related to deep Yucatan Channel (YC) transport, is examined and validated with a continuous 54-year simulation of the regional 1/25˚ Gulf of Mexico (GoM) Hybrid Coordinate Ocean Model (HYCOM). The hypothesis states that the imbalance of transport between the upper YC and the Florida Straits controls the rate of change of the LC volume and that the imbalance is compensated by transport through the deep YC....
Show moreA hypothesis by Maul [1977], stating the rate of change of Loop Current (LC) volume is related to deep Yucatan Channel (YC) transport, is examined and validated with a continuous 54-year simulation of the regional 1/25˚ Gulf of Mexico (GoM) Hybrid Coordinate Ocean Model (HYCOM). The hypothesis states that the imbalance of transport between the upper YC and the Florida Straits controls the rate of change of the LC volume and that the imbalance is compensated by transport through the deep YC. Previous studies have investigated the relationship between deep YC transport and LC area (used as a proxy for the volume). The first attempt by Maul et al. [1985] using a single mooring was unsuccessful in finding a relationship. However, Bunge et al. [2002] using data from the Canek observing program, which deployed 8 moorings across the YC, found a strong relationship between the deep YC transport and the LC area. The data used in Bunge et al. [2002] was for a period of 7.5 months, which is relatively short compared to the time scale of LC variability. A multi-decadal (54 years) HYCOM simulation of the Gulf of Mexico provides long term data to study LC variability and allows one to validate the Maul [1977] theory. Time evolution of the LC between two shedding events can be viewed as a combination of relatively high-frequency (on the order of about 40 days) fluctuations superimposed on a low-frequency trend. The high frequency portions of the modeled variability are shown to be related when the LC-area time derivative and the deep YC transport are compared. The low frequency variability is examined by comparing the LC-area time series with integrated transport in the deep YC, and statistically similar trends are identified. The results support the Maul [1977] theory.
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Date Issued: 2013
Identifier: FSU_migr_etd-8611
Format: Thesis

Title: Assessing Uncertainty in Simulated Atmospheric Transport and Dispersion Using a WRF-3DVAR Cycling Multiphysics Ensemble.
Creator: Riggi, Antonio Giuseppe, Fuelberg, Henry, Hart, Robert, Ahlquist, Jon, Department of Earth, Ocean and Atmospheric Sciences, Florida State University
Abstract/Description: This study examines the degree of uncertainty that occurs in atmospheric transport and dispersion (ATD) modeling due to using different parameterizations of physical processes such as shortwave and longwave radiative processes, precipitation formation, and atmosphere-surface interactions. An ensemble approach is taken to examine how this one aspect of meteorological model uncertainty affects subsequent ATD simulations. Differences in these Weather Research and Forecasting (WRF) physics...
Show moreThis study examines the degree of uncertainty that occurs in atmospheric transport and dispersion (ATD) modeling due to using different parameterizations of physical processes such as shortwave and longwave radiative processes, precipitation formation, and atmosphere-surface interactions. An ensemble approach is taken to examine how this one aspect of meteorological model uncertainty affects subsequent ATD simulations. Differences in these Weather Research and Forecasting (WRF) physics configuration strategies are investigated through their effects on offline HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) ATD simulations of three October 2010 tracer releases conducted in a region of complex terrain. The WRF model consists of three nested domains, with the innermost (highest resolution) domain having a horizontal grid spacing of 2 km. A twenty member ensemble of input meteorological data for the ATD simulations is generated through 6 h WRF cycling runs that employ three-dimensional variational data assimilation (3DVAR) on the outer two domains, but not on the innermost domain. Each of the twenty members uses a different combination of WRF physics parameterizations. Characteristics of several aspects of the 3DVAR system are presented. Single observation tests reveal increments that reflect physical balances imposed during the data assimilation process. Consistent RMS error reduction by 3DVAR improves the quality of information provided at the lateral boundaries of the innermost domain (∆x = 2 km). RMS errors of 10-meteruandvwinds are generally reduced by 0.4-0.5 m s−1, and RMS errors of 2-meter temperature are reduced by 1.5-3 K throughout the cycling runs. Considerable spread in PBL height, a key ATD variable, is produced in the innermost domain, especially during the daytime hours (σ = 141-200 m). HYSPLIT dispersion simulations using the ensemble members show a wide spread of ground-level concentration fields, as well as varying degrees of vertical transport, that are a consequence of the choice of model physics configurations, with plume areas sometimes varying by over 1000 km2. Verification metrics quantitatively illustrate the concentrations at the ground truth field study measurement stations that can be obtained by varying the model physics parameterizations. Ensemble-based probabilities provide a useful method of describing the likelihood that a given concentration will be exceeded.
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Date Issued: 2013
Identifier: FSU_migr_etd-8628
Format: Thesis

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