Numerical ocean models have become powerful tools for providing a realistic view of the ocean state and for describing ocean processes that are difficult to observe. Recent improvements in model performance focus on simulating realistic ocean interior mixing rates, as ocean mixing is the main physical process that creates water masses and maintains their properties. Below the mixed layer, diapycnal mixing primarily arises from the breaking of internal waves, whose energy is largely supplied by winds and tides. This is particularly true in abyssal regions, where the barotropic tide interacts with rough topography and where high levels of diapycnal mixing have been recorded (e.g., the Hawaiian Archipelago). Many studies have discussed the representation of internal wave generation, propagation, and evolution in ocean numerical models. Expanding on these studies, this work seeks to better understand the representation of internal wave dynamics, energetics, and their associated mixing in several different classes of widely used ocean models (e.g., the HYbrid Coordinate Ocean Model, HYCOM; the Regional Ocean Modeling System, ROMS; and the MIT general circulation model, MITgcm). First, a multi-model study investigates the representation of internal waves for a wide spectrum of numerical choices, such as the horizontal and vertical resolution, the vertical coordinate, and the choice of the numerical advection scheme. Idealized configurations are compared to their corresponding analytical solutions. Some preliminary results of realistic baroclinic tidal simulations are shown for the Gulf of Mexico. Second, the spurious diapycnal mixing that exists in models with fixed vertical coordinates (i.e., geopotential and terrain following) is documented and quantified. This purely numerical error arises because, in fixed-coordinate models, the numerical framework cannot properly maintain the adiabatic properties of an advected water parcel. This unrealistic mixing of water masses can be a source of major error in both regional and global ocean models. We use the tracer flux method to compute the spurious diapycnal diffusivities for both a lockexchange scenario and a propagating internal wave field using all three models. Results for the lock exchange experiments are compared to the results of a recent study. Our results, obtained by using three different model classes, provide a comprehensive analysis of the impact of model resolution choice and numerical framework on the magnitude of the spurious diapycnal mixing and the representation of internal waves. / A Dissertation submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2010. / September 29, 2010. / spurious mixing, numerical modeling, internal wave, tide / Includes bibliographical references. / Eric Chassignet, Professor Directing Dissertation; Carol Anne Clayson, University Representative; Louis St Laurent, Committee Member; Steven Morey, Committee Member; Markus Huettel, Committee Member; James O’Brien, Committee Member.

With the aid of a 3-part modeling system forced by various satellite-remote sensed atmospheric inputs controlled by cloudiness, this study: (1) describes the space-time variations of surface net CO2 flux exchange over the large scale Amazon basin, (2) determines the key factors controlling these variations, and ultimately (3) determines the optimal spatial configuration of a network of tower observing posts, which if deployed, could capture in area-wide averages the main variant properties of the Amazon basin's surface net carbon flux on an absolute basis. The philosophy guiding this research is that whereas a sufficiently detailed model can do very well in capturing the space-time gradients of carbon flux exchange and thus the relative source-sink properties of the Amazonian landscape, current modeling knowledge does not allow an adequate model determination of absolute source-sink properties. Direct observations are needed to obtain meaningful absolute accuracies of the source-sink properties, properties that are highly sensitive to environmental and bio-physiological factors that effectively produce a heterogeneous fabric of source and sink magnitudes across the basin at any given instant of time. However, for the Amazon basin, and as a general rule of thumb in carbon budget monitoring over a large expanse, there seems to be never enough observation posts to eliminate the systematic bias problem -- nor are those that do exist sited according to a network strategy that optimizes their collective ability to eliminate such a bias problem. A hydrometeorological model coupled to a mixed layer (ML) model of the planetary boundary layer (PBL) then equipped with a set of three CO2 assimilation models, and finally forced by high resolution satellite-retrieved incoming surface radiation fluxes and rainfall, forms a detailed carbon flux exchange modeling system linked to satellite inputs, that achieves the desired research objectives. The forcing of the model by remotely sensed solar/infrared radiative flux and rainrate variables, which exert dominant influences on the surface carbon budget and whose variant properties are determined by the position and diurnal timing of cloudiness, is an essential element of the modeling system. This is because one of the greatest shortcomings in prognostic modeling is the ability to reproduce real clouds, particularly convective clouds, in the right place at the right time. In understanding how environmental and bio-physiological factors exert their respective controls on carbon flux exchange variability, the underlying variables are classified into four categories: (1) meteorological factors; (2) radiation factors; (3) water cycle factors; and (4) bio-physiological factors. The three different CO2 assimilation models are investigated to achieve optimal performance insofar as obtaining validated surface carbon, heat, and moisture fluxes in the framework of the Florida State University (FSU) hydrometeorological model -- developed over the last decade by E.A. Smith & H.J. Cooper. Of the three carbon models examined, the one selected for the final net CO2 flux calculations was developed by G. Bonan, beginning with his Ph.D. dissertation research and now included in a land surface model (LSM) facility at NCAR. This carbon scheme contains a respiration component consistent with its photosynthetic component and physically couples the CO2, sensible, and latent heat fluxes through stomatal resistance. Test calculations of net ecosystem productivity (NEP) show that it is essential to model canopy-boundary layer interactions in order to reproduce observed morning CO2 effluxes measured at various forest sites located within Brazil and operated as part of the Large Scale Biosphere-Atmosphere Research Programme for Amazônia (LBA) -- specifically the LBA tower sites at Manaus and Jaru. This is because under typical conditions of a stable nocturnal PBL, the forest canopy remains stagnant, allowing carbon concentrations to become elevated until after sunrise when PBL stability flips and CO2 is rapidly vented into the atmosphere. In the PBL model developed for the study, CO2 concentrations and the concomitant fluxes are determined for five layers in and above the forest canopy following the progression of the ML during the daytime and the nocturnal boundary layer at night, which are treated as separate components of the diurnal PBL. It is important to point out that canopy heat capacity must be accounted for in the hydrometeorological modeling (an oft-overlooked factor in LSM modeling), to prevent sensible heat fluxes from being systematically overestimated. Values of observed canopy heat storage (needed in the development of the heat capacity scheme) are found using observed differences between net incoming radiation and sensible-latent heat fluxes, or observed total residual energy. Calibration and validation of CO2, sensible, and latent fluxes at the three LBA tower sites are accomplished using modeled total residual energy at the forest sites and modified photosynthesis parameters at the pasture site. Application of the modeling system over the large-scale Amazon basin shows that while vegetation type is the most important factor controlling area-wide CO2 fluxes, incoming surface solar radiation and ambient temperature (both directly responsive to the cloud field) are the primary factors producing spatial and temporal variability of CO2 fluxes at a given location. Modeled CO2 fluxes show mean monthly uptake values in the range of 1-3 mmol m-2 s-1. Due to the superimposed annual and daily march of the solar elevation angle, diurnal progressions of large coherent expanses of CO2 efflux over forest areas, progressing from SE to NW in December and from NE to SW in June, are an essential variational mode in the surface carbon budget. Inspection of area-wide modeled fluxes near the tower sites reveals that the systematic use of ECMWF-analyzed winds and temperatures in forcing the modeling system creates instances of spurious nocturnal stability that produce larger morning efflux magnitudes than observations suggest. Finally, CO2 fluxes at some 20,000 forest grid points within the Amazônia region and for eight months of model output, are analyzed to determine the optimal sampling configuration vis-à-vis capturing in area-wide averages, the space-time variability of net CO2 flux. These results lead to the conclusion that flux observations from five strategically placed towers, measuring in conjunction with the existing three LBA towers at Manaus and Jaru, would be sufficient in baselining area-wide net CO2 fluxes needed for an understanding of carbon sequestration within the Amazon basin on an absolute scale. / A Dissertation submitted to the Department of Meteorology In partial fulfillment of the Requirements for the degree of Doctor of Philosophy. / Spring Semester, 2004. / March 4, 2004. / Amazon, Carbon Cycle, Variability, Carbon / Includes bibliographical references. / Eric A. Smith, Professor Co-Directing Dissertation; Paul H. Ruscher, Professor Co-Directing Dissertation; James B. Elsner, Outside Committee Member; Henry E. Fuelberg, Committee Member; Carol A. Clayson, Committee Member.

This dissertation examines the role of microorganisms in marine biogeochemical cycles with a particular emphasis on sedimentary nitrogen transformations. Nitrogen is required by all living organisms and is a key nutrient controlling the productivity of Earth's oceans. Pervasive endeavors of modern human society, such as fossil fuel combustion and Haber-Bosch N2 fixation for agricultural fertilizers, have caused large-scale perturbations in the natural, global nitrogen cycle such that the rate of anthropogenic reactive nitrogen creation now exceeds that of all natural processes combined. A substantial fraction of this man-made reactive nitrogen is being lost to the environment where, as a macro-nutrient, excessive nitrogen loading is causing extensive disruptions to natural primary production cycles and food webs. Basic scientific research on nitrogen cycling in coastal oceans is imperative as human activities are increasingly adding to the reactive nitrogen influx to near-shore environments. Shallow coastal areas (< 200 m water depth) cover only ~ 7% of the ocean although up to 30% of marine primary production occurs in these zones. Biogenic debris settling in coastal zones largely escapes degradation in the water column, and thus, as much as 60% of locally-produced organic matter undergoes benthic deposition and diagenesis. Nutrients regenerated during organic matter mineralization in shallow sediments are essential in fueling high rates of marine primary production in continental margins. Coastal sediments are also important sites of reactive nitrogen removal with the majority of marine microbial N2 production occurring in these areas. Production of N2 in continental shelf sediments via microbial denitrification and anammox (anaerobic ammonium oxidation) is an essential process for nitrogen removal and maintaining a balance of reactive nitrogen in the oceans. Denitrification and anammox are two of the least understood pathways in the nitrogen cycle; explorations of rates and mechanisms for N2 production have been hindered mainly by methodological difficulties, spatial and temporal variability in benthic processes, and previously-overlooked nitrogen cycling pathways. Due largely to a paucity of direct N2 flux rate measurements, most global marine nitrogen budget estimates are tenuous (Capone 2008). Thus, the foci of this dissertation were to better constrain known rates of denitrification and anammox, elucidate the principal controls on these processes in situ, and explore the ecology of microorganisms mediating these reactions in coastal sediments. Rates and controls of nitrogen removal by microbial N2 production were studied at three field areas in two different estuaries. Field research sites within the Apalachicola National Estuarine Research Reserve included stations adjacent to St. George Island in the Gulf of Mexico (for the investigation of nitrogen cycling in permeable sediments) in addition to stations within an oligohaline marsh near the mouth of the Apalachicola River (for a study of nitrogen removal by coastal wetlands). Benthic microbial nitrogen cycling was also studied in fjords of the Svalbard islands in the Arctic Ocean. The first of four chapters of this dissertation describes a study identifying the microbial taxa which catalyze phytodetritus degradation and denitrification in permeable coastal sediments of the northeast Gulf of Mexico. Coastal benthic environments typically receive intermittent pulses of organic matter following phytoplankton bloom events and permeable sediments have been demonstrated to rapidly degrade this material. Microorganisms act as the primary agents of benthic organic matter decomposition through the production of extracellular hydrolytic enzymes, fermentation, and terminal carbon mineralization coupled with respiratory processes. Although the role of bacteria in the decomposition of organic matter in marine sediments has long been recognized, the mechanisms regulating organic matter decomposition, and relationships between the phylogeny of benthic microorganisms and changes in biogeochemical and ecological function, are under-explored. In this study of detritus-degrading microorganisms, stable isotope probing experiments were used to track the assimilation of isotopically-labeled substrate into bacterial DNA and to directly link the taxonomic identification of benthic microorganisms with particulate organic matter degradation and denitrification activity. Phytodetritus deposition events were simulated in the laboratory by the addition of 13C-enriched, heat-killed Spirulina cells to intact sediment core incubations. Immediate increases in O2 consumption, N2 efflux, and dissolved inorganic nitrogen efflux were observed following phytodetritus addition relative to unamended treatments, suggesting that the benthic microbial community was poised to immediately begin oxidizing deposited organic matter. Analyses of 16S rRNA gene sequences amplified from 13C-enriched DNA fractions demonstrated that members of the Gammaproteobacteria (Vibrionales and Alteromonadales), Deltaproteobacteria, Actinobacteria, Verrucomicrobia, and Planctomycetes metabolized the phytodetritus amendment. Terminal restriction length polymorphism analyses showed increases in the relative abundance of Gammaproteobacteria, Planctomycetes, and Bacteroidetes with phytodetritus addition. Alphaproteobacteria were identified as metabolically active denitrifiers by phylogenetic analysis of nitrous oxide reductase gene sequences from 13C-enriched DNA fractions. This study provides the first identification of microorganisms responsible for organic matter degradation in marine sediments by DNA sequence analysis. Microbial assemblages recognized for high molecular weight organic matter oxidation in the marine water column were important in catalyzing these processes in permeable sediments. Permeable sediments are also the focus of Chapter 2 which describes nitrogen cycling over a one-year period in sublittoral sands from two contrasting sites near St. George Island. Nitrogen stable isotope tracer techniques were used to measure N2 production rates and pathways in sediment cores and slurries. To simulate pore-water advection, which occurs in permeable sands due to interactions between water currents and surface topography, intact sediment cores were perfused with aerated seawater. Pore-water perfusion increased denitrification rates up to 2.5-fold and 15-fold for the Apalachicola Bay and Gulf of Mexico sites, respectively, relative to static cores. Seasonal N2 production rates were highest in spring and fall. Denitrified nitrate was derived almost entirely from benthic nitrification at the Gulf site whereas water column nitrate was more important at the Bay site. Stirred chambers with intact sediment cores were used to determine net fluxes O2, N2, nitrate, and ammonium across the sediment-water interface during varied degrees of continuous pore-water exchange. Rates of N2 efflux were directly correlated with the extent of pore-water flow increasing from 0.13 mmol N m-2 d-1 under diffusion-limited solute transport conditions up to 0.87 mmol N m-2 d-1 with pore water advection. Mineralized nitrogen was completely converted to N2 gas in Gulf of Mexico sediments. These data provide clear evidence that permeable sediments are important in nitrogen removal and N2 production occurs over a continuum of rates dependent on bottom current conditions. Results from a study of benthic nitrogen cycling in two Arctic fjords are presented in Chapter 3. Intact sediment core incubations were used to quantify net fluxes of dissolved inorganic nitrogen, organic nitrogen, organic carbon, and oxygen at the sediment-water interface. Rates of gross denitrification, anammox, nitrification, dissimilatory nitrate reduction to ammonium, and N2 fixation were quantified using core incubations and slurry experiments. Profiles of dissolved inorganic nitrogen in pore-water, and organic carbon and nitrogen in the solid phase, were also obtained. Net nitrogen losses as N2 ranged from 0.152 to 0.453 mmol N m-2 d-1 and denitrification comprised 2% to 11% of total carbon oxidation. Rates of anammox ranged from 20 to 51 μmol N m-2 d-1 and contributed 5% to 23% of gross N2 generation. Nitrification rates were as high as 0.833 mmol N m-2 d-1 and sediments were a substantial source of nitrate to the water column (0.169 to 0.393 mmol N m-2 d-1 efflux). Uptake of ammonium (0.052 to 0.087 mmol N m-2 d-1), dissolved organic nitrogen (0.291 to 0.486 mmol N m-2 d-1), and dissolved organic carbon (1.31 to 2.50 mmol N m-2 d-1) was observed. Benthic nitrogen fixation was estimated at 0.020 mmol N m-2 d-1 in one of the fjords. Dissimilatory nitrate reduction to ammonium and net N2O production were not detected. This study provides direct evidence that nitrogen loss rates, mainly via denitrification, in Arctic sediments rival those measured in temperate or subtropical environments. Chapter 4 describes a study sponsored by the NOAA National Estuarine Research Reserve System Graduate Research Fellowship program to investigate nitrogen cycling in the Apalachicola River distributary marsh. Coastal, fringing marshes have been thought to remove dissolved inorganic and particulate nitrogen from external sources via benthic denitrification and burial, respectively, and to export considerable loads of dissolved organic nitrogen (DON) to the greater estuary. There is, however, little data available from tidal freshwater and oligohaline marshes to confirm these hypotheses and benthic nitrogen cycling in the Apalachicola National Estuarine Research Reserve (ANERR) marsh has not been previously studied. This work addressed the hypotheses that the ANERR marshes comprise a significant sink of river-derived dissolved inorganic nitrogen through nitrification-denitrification and burial, and provide a substantial source of nitrogen to the Bay as DON. Denitrification rates were measured between July 2006 and August 2008 using intact sediment core incubations. Rates of net N2 flux ranged from 0.23 to 1.72 mmol N m-2 d-1 with a mean of 0.72 mmol N m-2 d-1 for all sites over the course of the study. Preliminary results indicate that burial of particulate nitrogen (1.46 mmol N m-2 d-1) is a larger annualized loss term than denitrification. A study of tide-driven exchange of nitrogen between marsh creeks and river distributaries showed net uptake of nitrate by marsh sediments and export of DON. / A Dissertation submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Summer Semester, 2009. / April 27, 2009. / Nitrogen, Anammox, Marine, Biogeochemistry, Denitrification, Estuary / Includes bibliographical references. / Joel Kostka, Professor Directing Dissertation; Munir Humayun, Outside Committee Member; Jeff Chanton, Committee Member; Stefan Green, Committee Member; Markus Huettel, Committee Member.

Dissolved organic matter (DOM) is well known for its strong binding capacity for trace metals. In order to better predict the role of DOM in the speciation and transport of trace metals in the environment capillary electrophoresis (CE), a molecular separation technique, was coupled to a Sector Field Inductively Coupled Plasma Mass Spectrometer (SF-ICP-MS). The combination of these two techniques allows for the study of non-labile metal speciation in aquatic samples. An extensive theoretical analysis of metal-ligand separations on the molecular scale of a CE experiment was combined with numerical simulations and experimental tests to assure accurate quantitative results. It was found that the susceptibility of metal-ligand complexes to dissociation during a CE separation can be conveniently captured with a theoretical approximation of complex half-life. Complex half-life, thus is proposed to serve as a tool for assessing the likeliness of quantitative artifacts in CE-ICP-MS. By separating lanthanide complexes with EDTA and Humic Acids (i.e. strong stable ligand competition) we have been able to determine equilibrium binding constants for all 14 stable rare earth elements (REEs), Sc and Y with Suwannee river fulvic acid (SRFA) and Leonardite humic acid (LHA) at near environmental conditions (pH 6-9, 0.01 – 0.01 mol.L-1 NaNO3, 100 nmol.L-1 Ln, 10 mg.L-1 HS). Conditional binding constants for LnHS (Kc) were found to increase gradually by 2-3 orders of magnitude from La to Lu. This increasing relative affinity reflects the lanthanide contraction, a basic chemical property of the REEs related to the gradual decrease in ionic radius from La to Lu. LogKc values were found to gradually increase with increasing pH and decrease with increasing ionic strength. Additionally, LHA logKc's were on average 1.5 log units higher than SRFA logKc's with a total range of 9.0 / A Dissertation submitted to the Department of Geological Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester, 2003. / October 31, 2003. / Lanthanides, Binding constant, Humic substances, ICP-MS / Includes bibliographical references. / Vincent J. M. Salters, Professor Directing Dissertation; William M. Landing, Outside Committee Member; William T. Cooper, Outside Committee Member; Louis Claude Brunel, Outside Committee Member; A. Leroy Odom, Committee Member; Yang Wang, Committee Member.

Includes bibliographical references (leaves 110-115). / The propagation of the Global Positioning System (GPS) signal from the satellite to the receiver is affected by, among other factors, the atmosphere through which it passes and, whereas the affects of the ionosphere can be eliminated by the differencing of two transmitted frequencies, the affects of the troposphere remain one of the major sources of noise in traditional geodetic and positioning applications of GPS. This noise can, however, be turned into a signal for the meteorologist and, by applying suitable constraints and processing strategies, it is possible to estimate the amount of precipitable water vapour (PWV) in the atmosphere. The application of the GPS data for the estimation of PWV in the atmosphere is not a new concept and has been described in numerous publications and reports since the early 1990's (Bevis et al., 1992, Rocken et al., 1993). This project is, however, an attempt to test the technique using the South African network of permanent GPS base stations. This thesis sets out to answer four fundamental questions: i. In theory, can GPS observations be used to estimate the amount of precipitable water vapour (PWV) in the atmosphere? ii. What permanent GPS networks are being used in other countries around the world for similar applications and how successful are these applications? iii. Can data derived from the South African network of permanent GPS base stations, TrigNet, be used to estimate PWV with sufficient accuracy to be able to supplement the radiosonde upper air measurements of the South African Weather Service (SAWS)? iv. Is the estimation of PWV as derived from the GPS observations a true reflection of reality using the radiosonde ascent measurements and numerical weather model (NWM) data as a method of independent verification? The primary data sets used to estimate atmospheric PWV at hourly intervals for March 2004 were; i. GPS data derived from the South African network of permanent GPS base stations provided by the Chief Directorate of Surveys and Mapping (CDSM); and ii. Surface meteorological measurements supplied by the South African Weather Service (SAWS). The two independent data sets used to verify and test the technique were; i. Upper air measurements derived from radiosonde ascents provided by the SAWS. These measurements were used to compute Integrated Water Vapour (IWV) and then converted to PWV; and ii. PWV estimates derived from a Numerical Weather Model provided by the Department of Environmental and Geographical Sciences of UCT. By the comparing the estimates of PWV from the three techniques, viz. GPS, radiosonde and NWM, it was found that GPS will meet the accuracy requirements of the meteorologist and could be used to supplement radiosonde measurements for use in numerical weather models.

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

Integrated kinetic energy (IKE) is a recently developed metric that approximates the destructive potential of a tropical cyclone by assessing the size and strength of its wind field. Despite the potential usefulness of the IKE metric, there are few, if any, operational tools that are specifically designed to forecast IKE in real-time. Therefore, IKE and tropical cyclone structure are analyzed within historical Atlantic tropical cyclones from the past two decades in order to develop an understanding of the environmental and internal storm-driven processes that govern IKE variability. This analysis concurs with past research that IKE growth and decay is influenced by both traditional tropical cyclone development mechanisms and by other features such as extratropical transition and trough interactions. Using this framework, a series of statistical prediction tools are created in an effort to project IKE in Atlantic tropical cyclones from a series of relevant normalized input parameters. The resulting IKE prediction schemes are titled the "Statistical Prediction of Integrated Kinetic Energy (SPIKE)". The first version of SPIKE utilizes simple linear regression to project historical IKE quantities in a perfect prognostic mode for all storms between 1990 and 2011. This primitive model acts as a proof of concept, revealing that IKE can be skillfully forecasted relative to persistence out to 72 hours by even the simplest of statistical models if given accurate estimates of various metrics measured throughout the storm and its environment. The proof-of-concept version of SPIKE is improved upon in its second version, SPIKE2, by incorporating a more sophisticated system of adaptive statistical models. A system of artificial neural networks replaces the linear regression model to better capture the nonlinear relationships in the TC-environment system. In a perfect prognostic approach with analyzed input parameters, the neural networks outperform the linear models in nearly every measurable way. The system of neural networks is also more versatile, as it is capable of producing both deterministic and probabilistic tools. Overall, the results from these perfect prognostic exercises suggest that SPIKE2 has a high potential skill level relative to persistence and several other benchmarks. Finally, in an effort to assess its real-time performance, the SPIKE2 forecasting system is run in a mock-operational hindcast mode for the 1990 to 2011 North Atlantic hurricane seasons. Hindcasts of IKE are produced in this manner by running the neural networks with hindcasted input parameters from NOAA's second generation Global Ensemble Forecast System reforecast dataset. Ultimately, the results of the hindcast exercises indicate that the neural network system is capable of skillfully forecasting IKE in an operational setting at a level significantly higher than climatology and persistence. Ultimately, forecasts of IKE from these neural networks could potentially be an asset for operational meteorologists that would complement existing forecast tools in an effort to better assess the damage potential of landfalling tropical cyclones, particularly with regards to storm surge damage. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester, 2015. / March 19, 2015. / Atlantic Hurricanes, Integrated Kinetic Energy, Statistical Prediction, Tropical Cyclone Structure, Tropical Meteorology / Includes bibliographical references. / Vasubandhu Misra, Professor Directing Dissertation; Ming Ye, University Representative; Robert E. Hart, Committee Member; Philip Sura, Committee Member; Allan J. Clarke, Committee Member; Mark D. Powell, Committee Member.

Since 1980, a new type of ENSO, i.e., central Pacific (CP) ENSO, where sea surface temperature anomalies (SSTAs) are mainly located in the equatorial central Pacific, has been frequently observed. Several studies have documented and predicted a higher occurrence ratio of CP ENSO to eastern Pacific (EP) ENSO, where SSTAs mainly occur in the equatorial eastern Pacific, in a warming climate. Most studies centered on the difference between CP and EP ENSO have used traditional analysis methods, such as PCA/EOF analysis and regression, to define or differentiate the aforementioned two types of ENSO. However, the results obtained using these methods can only reveal accumulated spatial information which contributed most to the variance of the data, which is the usually the spatial information during the mature (peak) stage of ENSO; this spatial information is a static pattern and is not able to reveal sequential development of ENSO, which should be crucial for physical interpretations. In addition, although this spatial information in generally true for the entire temporal span, it is not necessarily true for any subperiods and thus not able to reveal any potential characteristic change of ENSO over time. In this study, an alternative Niño 3.4 index is defined to reflect only the interannual variability of equatorial Pacific SSTAs. Using this alternative index, we identify 28 El Niño events and 31 La Niña events. Then, we employ a newly developed analysis method, i.e., fast multidimensional ensemble empirical mode decomposition (FMEEMD), to extract the interannual spatiotemporal evolution of SSTAs to examine the developments of the identified ENSO events. All events are classified into four types of ENSO based on the interannual evolutions of SSTAs early in the development stage: (1) EP ENSO, (2) eastern-central Pacific (ECP) ENSO, (3) western-central Pacific (WCP) ENSO, and (4) mixed (MIX) ENSO. We apply the same method to analyze surface horizontal wind and thermocline depth data, and phase composite analyses on SSTAs, surface wind anomalies and thermocline depth anomalies are performed for each type of El Niño events. The results show four distinctive evolution patterns; it is found that La Niña events also have similar variation in the evolution patterns. The lower-frequency variability and change (decadal and longer time scales, including secular trend trend) in SSTAs, surface wind anomalies and thermocline depth anomalies are also examined. The secular trends show weak surface cooling over the central Pacific between 140°W and 160°W near the Equator, consistent with the anomalous wind divergence and thermocline shoaling in the same region. In response to decadal and lower-frequency oscillatory wind forcing, the background state of the thermocline is modified in a way that when western-central Pacific is dominated by shoaling (deepening), the eastern Pacific is dominated by deepening (shoaling). The combined effect of the secular trends and lower-frequency oscillatory variability is that for some decade(s), the thermocline depth is anomalously shallower (deeper) in the western-central Pacific region, while the thermocline depth is anomalously deeper (shallower) in the east. We suggest that this "seesaw" pattern in the depth anomalies across the Equator determines the evolving patterns of ENSO by hinder/facilitating the communication between ocean surface and subsurface, and thus modifying the effect of wave-associated thermocline displacements on SST change over the western-central Pacific. Additionally, for WCP and some of the MIX ENSO events, a potential SSTA precursor from Baja California/northeastern Pacific might be instrumental to the subsequent development, possibly by inducing zonal wind anomalies in the western Pacific. / A Dissertation submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the Doctor of Philosophy. / Spring Semester, 2015. / April 6, 2015. / ENSO, FMEEMD, SST / Includes bibliographical references. / Zhaohua Wu, Professor Directing Dissertation; Ming Ye, University Representative; Allan Clarke, Committee Member; Guosheng Liu, Committee Member; Philip Sura, Committee Member.

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 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. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / November 5, 2014. / Air-Sea Interaction, Numerical Modeling, Sea Surface Temperature, Tropical Cyclones, Tropical Meteorology / Includes bibliographical references. / Mark Bourassa, Professor Co-Directing Thesis; Robert Hart, Professor Co-Directing Thesis; Mark Powell, Committee Member; Vasu Misra, Committee Member.

Clouds play an important role in the earth's energy budget, and changes in their properties can remarkably impact the amount of warming in response to greenhouse gas increases. In this study, we applied the Coupled Feedback Response Analysis Method (CFRAM) to estimate the contributions of cloud property changes to the magnitude of the annual mean-surface temperature response in a transient simulation where CO2 increases at rate 1% yr-1 , using the NCAR Community Climate System Model, version 4 (CCSM4). To examine closely the contributions of changes in cloud properties to the annual mean-surface temperature, the full-cloud level is divided into three levels in terms of the cloud-top pressure (CTP). This study found that the annual and global mean-surface temperature response is a warming of (+0.175 oK) due to the net cloud feedback that comes mainly from the positive SW cloud feedback. The medium (400 < CTP < 700 mb) clouds changes are the dominant contributors (+0.175 oK) to the surface warming due to their magnificent positive SW cloud feedback (+0.33 oK). High (CTP < 400 mb) clouds changes cause a weak negative contribution (-0.0218 oK) to the surface warming because of the close cancellation between their large negative SW and large positive LW high-cloud feedbacks. Low (CTP > 700 mb) cloud changes are the least contributors to SW and LW cloud feedbacks (positive SW and negative LW); however, they still contribute positively (+0.0217 oK) to the net cloud feedback with an absolute magnitude that is almost equal to the contribution of the high-cloud changes. Furthermore, this study found that the annual mean-surface temperature increases in the Polar Regions (60o-90o in both hemispheres) are due to the positive LW cloud feedback from the changes in the three cloud levels, mostly due to positive LW medium-cloud feedback. However, the annual mean surface warming for the region covered between (60o S-60o N) is due to the positive SW low- and medium-cloud feedbacks. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / November 13, 2014. / CFRAM, Climate Change, Cloud Effect, Cloud Feedback, Cloud Properties, surface warming / Includes bibliographical references. / Ming Cai, Professor Directing Thesis; Guosheng Liu, Committee Member; Zhaohua Wu, Committee Member.