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Atmospheric conditions during the dry season of the South American monsoon are instrumental in the initiation of convection during the wet season and are strongly correlated to SSTs within the Atlantic Warm Pool. Subsequently, accurate seasonal prediction of temperature and rainfall during the dry season has the potential to improve our understanding of and the predictability of these variables during future seasons. In this study, we review the fidelity of South American dry season (June-July-August) reforecasts from one global climate model (GCM), and one downscaled regional climate model (RCM). Additionally, we evaluate a second integration of the RCM that uses a bias correction method called anomaly nesting, which is designed to remove the bias of the GCM before the downscaling process is performed. The models are integrated for seven dry seasons (2001–2007), and each season consists of six ensemble members. For this study, we focus on two primary regions: the Amazon River Basin (ARB) and the subtropical region (ST). There are three objectives of this research. The first is to locate regions of model bias for two-meter air temperature and for precipitation within the ARB and the ST using NCEP Climate Forecast System Reanalysis (CFSR) as a comparison dataset. The second is to evaluate the predictability of above normal, normal, and below normal occurrences of the two variables using potential predictability ratios and calculations of the area under the relative operative characteristic (ROC) curve (AUC). Through this analysis we should be able to determine whether downscaling or anomaly nesting improve upon the skill of the GCM. Lastly we wish to evaluate how the three models depict land-atmosphere interactions during the dry season and compare their results with results from CFSR. The models produced the largest biases of both variables over elevated terrain and within the Intertropical Convergence Zone (ITCZ). However, neither of these locations significantly impacts the ARB or the ST. Signal-to-noise ratios show that the ARB exhibits more potential predictability than the ST and that temperature exhibits more potential predictability than precipitation. AUCs confirm that temperature is more skillfully predicted than precipitation and that the models exhibit more skill in the ARB than in the ST. AUCs show that the downscaled and the downscaled with anomaly nesting integrations display more skill than the GCM integration, particularly in the ARB. Lastly, we find conflicting results between the models and CFSR regarding how the land and the atmosphere interact during the dry season. However, a full moisture budget analysis is needed to completely resolve land-atmosphere feedbacks and that is beyond the scope of this study.

A Thesis submitted to the Department of Earth Ocean and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Masters of Science.

Spring Semester, 2011.

March 17, 2011.

RSM, CFS, Anomaly Nesting, Climate Model

Vasubandhu Misra, Professor…

Advisors/Committee Members: Vasubandhu Misra (professor directing thesis), Henry Fuelberg (committee member), Philip Sura (committee member).

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The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze that is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning dominated the ARCTAS-A period and has been the focus of many ARCTAS related studies. This study determines the common pathways for anthropogenic emissions during ARCTAS-A. Trajectories are released each day from three historically significant regions of anthropogenic emissions (Asia, North America, and Europe). These fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectories then are examined to determine: Origins of emissions that reach the Arctic (defined as 70oN), pathways of the emissions reaching the Arctic, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. These results serve as regional "climatologies" for the ARCTAS-A period. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled by the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived "climatologies" and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases.

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, 2010.

September 30, 2010.

ARCTAS, Pollution, Anthropogenic, Emissions, Arctic, Arctic Haze, Transport, Trajectories

Henry E. Fuelberg, Professor Directing Thesis; Guosheng Liu, Committee Member; Robert Hart, Committee Member.

Advisors/Committee Members: Henry E. Fuelberg (professor directing thesis), Guosheng Liu (committee member), Robert Hart (committee member).

▼  Karst landscapes cover approximately 20% of the ice-free land area worldwide. The soluble nature of the bedrock within a karst landscape allows for the formation of caverns, joints, fissures, sinkholes, and underground streams, which affect the hydrological behavior of the region. Currently, the Noah Land-Surface Model (Noah- LSM), coupled with the Weather Research and Forecasting (WRF) model, does not provide a representation of the physical behavior of a karst terrain. Previous research has attempted to model karst behavior through soil moisture and land cover/land use changes to determine the influence this unique landscape may have on atmospheric phenomenon. This highlights the need to study the potential influence that karst landscapes may have on model simulations. For this study, several factors were taken into account while studying karst and meteorology: the verification of a current operational forecasting model against observational data over five years (2007 to 2011), the formation of a karstlike soil type for use within an operational forecasting model, and model behavior once this karst-like soil type was added to the operational forecasting model. The verification of a currently operational forecasting model, the North American Mesoscale (NAM), indicated that, overall, the karst regions may exhibit an influence on local winds (greater error) and precipitation (frequency and forecasting). When developing a realistic karst-like soil proxy for use in the Noah-LSM, hydraulic conductivity values show a variation ranging from around 10-7 and 10-5 m s-1 for the karst bedrock within Tennessee and Kentucky. Sandy loam and clay soils were used, along with bedrock parameters, to determine an average soil parameter type for the epikarst bedrock located within this region. The model study demonstrated that the addition of karst highlighted the potential influence on precipitation distribution and energy fluxes, through RMSD and R2 values taken at a 95% confidence interval. Advisors/Committee Members: Xingang Fan (Director), Jason Polk, Rezaul Mahmood.

▼  The Intertropical Convergence Zone (ITCZ) is a feature that results from the ocean-atmosphere interactions in the tropics around the world. The ITCZ is characterized by surface wind convergence, tall storm clouds, and it forms a belt of high time-averaged precipitation around the globe. The ITCZ undergoes seasonal migrations between 5°S and 15°N roughly following the subsolar point on Earth with the seasons, with a mean annual position located slightly above the Equator, between 2° and 5°N. This study tested the hypothesis that there was a northward shift in the median position of the ITCZ in the first decade of the 2000’s relative to the 1900’s. This hypothesis has been posed in the literature given a weakening in the intensity of the Trade Winds observed in the southern Caribbean Sea during the first decade of the 2000’s, with concomitant ecological impacts due to weakening in coastal wind-driven upwelling. The hypothesis was tested by analyzing variations in the monthly latitudinal position of the ITCZ over the Atlantic Ocean relative to the median position computed for the period 1987–2011. The position of the ITCZ was derived from satellite-derived ocean surface wind measurements collected from 1987 to 2011. A Mann-Kendall analysis and a Monte Carlo simulation were used to test for trends in the median cross-basin latitudinal position of the ITCZ. The study included an analysis of regional changes across the tropical central Atlantic (50°W to 15°W), the Western Atlantic (50°W to 30°W), and the Eastern Atlantic (30°W to 15°W) within the tropics. The results show a slight southward trend in the median position of the ITCZ over the central Atlantic and also in the Eastern Atlantic in the first decade of the 2000’s relative to the 1990’s. While this trend is barely significant, it is likely simply due to interannual variation in the average annual position of the ITCZ. The data were also examined for the timing and persistence of a double ITCZ in the Atlantic. The double ITCZ over the Atlantic appeared every year in February or March, with the largest separation between the northern and southern branches of the ITCZ observed in June and July. The possible effects of changes in the average latitudinal position of the ITCZ on the upwelling in the Cariaco Basin (southeastern Caribbean Sea off Venezuela) were also examined. Anomalies of the median of the latitudinal position of the ITCZ in the Atlantic were compared with anomalies of in-situ temperature collected during the 1990’s and the first decade of the 2000’s by the CARIACO Ocean Time-Series program and with anomalies of satellite SST (from the Advanced Very High Resolution Radiometer satellite; AVHRR) from 1995 to 2016. Correlation analysis were performed between anomalies of water temperatures at various depths and anomalies of satellite SST with anomalies of the monthly mean ITCZ position with lags up to 3 months for the time series, and…

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A simple one-dimensional seasonal atmosphere-ocean energy balance model is used to study the seasonal and latitudinal response of the model climate to a doubling of the CO2 concentration. A new climate feedback analysis method, formulated in Lu and Cai (2009a), is used to isolate contributions (partial temperature changes) of the external forcing alone and subsequent feedbacks to the total temperature change experienced by the model climate. In this study, the relative importance of the external forcing alone (the CO2 doubling), surface ice-albedo feedback, water vapor feedback, changes in poleward heat transport, changes in vertical sensible heat flux, and changes in heat storage are analyzed. The partial temperature change due to the water vapor feedback is substantially the largest contributor to the globally averaged surface warming. The ice-albedo feedback plays a smaller role, but also significantly contributes to the overall warming of the surface. The most important negative feedback, counteracting the surface warming, is the change in the vertical sensible heat flux. However, though the water vapor feedback is most responsible for the overall surface warming, it is not the feedback most responsible for the seasonal and spatial pattern of the surface warming. The climate of this model indicates that there is a surface polar warming amplification, with a maximum occurring in late summer/early fall. The feedback most responsible for this polar warming amplification and seasonal pattern in this model is the surface ice-albedo feedback, which is largest at high latitudes in summer.

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.

Degree Awarded: Summer Semester, 2011.

Date of Defense: April 6, 2011.

CFRAM, Climate Feedbacks, Global Warming, Polar Amplification

Ming Cai, Professor Directing Thesis; Robert G. Ellingson, Committee Member; Zhaohua Wu, Committee Member.

Advisors/Committee Members: Ming Cai (professor directing thesis), Robert G. Ellingson (committee member), Zhaohua Wu (committee member).

▼ Although tropical cyclone (TC) track forecasts have improved considerably in recent years, predicting their intensity continues to be a challenge for both meteorologists and numerical models. A storm's path is primarily influenced greatly by large-scale atmospheric circulations; however, its strength appears to be dominated both by large scale influences and small-scale mechanisms within the storm itself. Most previous research on TC intensity change has employed either numerical modeling or diagnostic approaches using traditional meteorological parameters. Only recently have studies begun to examine electrification as a means for assessing the potential for intensification. Several papers have considered lightning as a proxy for storm intensification, mostly using data from Vaisala's National Lightning Detection Network (NLDN) and Long-Range Lightning Detection Network (LLDN). However, they mostly have examined individual TCs. This study uses LLDN data to study 45 Atlantic Basin TCs between the years 2004 and 2008. Using the National Hurricane Center's (NHC) best track dataset, lightning data are collected for each TC out to a 500 km radius. Parameters including storm intensity, intensity change, environmental vertical wind shear, storm motion, and flash count are compiled at each NHC best track position. The data at each position then are categorized in several ways, including change in intensity. These methods allow us to examine relations between composites of storm intensity/intensification and convective distribution and frequency. Distributions of cloud-to-ground (CG) flash density with respect to storm motion and speed show that lightning generally is preferred in the TCs' right front and right rear quadrants. Hurricanes produce the greatest flash densities during relatively slow forward motion, while tropical depressions and tropical storms exhibit greater flash densities during faster forward motion. Storm-relative CG flash distributions during weakening, no pressure change, and slow intensification (-5 to 0 hPa 6 h-1) exhibit the same right front and rear quadrant preference as the TC intensity categories. Flash densities are greatest during periods of faster intensification, with a nearly symmetric presentation in the inner core region. When computing flash densities with respect to environmental deep layer wind shear, TCs exhibit a strong preference for lightning in the downshear left and right quadrants of the inner core (0-100 km) and outer rainbands (100-300 km), respectively. Tropical storms and hurricanes best show this relation, with TDs exhibiting a stronger preference for lightning in the downshear right quadrant. Relatively weak wind shear produces greater flash densities in all TC intensity categories. Conversely, storms experiencing strong shear exhibit smaller flash densities in all TC categories due to the disruption of deep convection. During periods of faster intensification, maximum flash densities are located in the inner core, with weakening, no change, and slow intensification periods… Advisors/Committee Members: Henry Fuelberg (professor directing thesis), Robert Hart (committee member), Paul Ruscher (committee member).

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Particle-laden buoyant jets (PBJ) are free-convective flows that contain particles. Many studies have examined pure thermal plumes, discussing a symmetric self-similar structure that is common in the plume literature. Other studies have studied the fallout properties of particles embedded in plumes. Many contaminant transport models use a Gaussian, self-similar plume profile and treat particles only as a passive tracer. There is however no evidence in the literature of the simultaneous examination of both particle loading and temperature on the flow regimes of a PBJ. Twenty-five numerical simulations were implemented using the LANL HIGRAD numerical model, to systematically study the resulting flow regimes as the temperature and particle loading of a PBJ were systematically varied. A supplemental experiment was carried out in the laboratory, with three simulations carried out that were dynamically similar to the experiment. The comparison between experiment and simulation indicated that the model did not create turbulence as close to the domain floor as in the experiment, and further tuning is required. With awareness of this inconsistency, the twenty-five simulation results produced results of significant interest. Only two of the twenty-five simulation results produced the self-similar, Gaussian profile that is observed in the plume literature. Four of the twenty-five cases produced a no collapse PBJ scenario. The remaining cases produced either a partial collapse or full collapse of the PBJ. The use of the Grashof and buoyant Richardson numbers to characterize the flow regimes did not produce consistency with the resulting flow regime. A modified multiphase Richardson number however, accounting for particle density within a control volume, showed consistency with the resulting flow regime and indicates promise for further research and perhaps operational use. PBJ are physically relevant to a variety of particle-laden convective flows including volcanoes, industrial emissions, and contaminant transport. These results are of interest to a number of stakeholders including the DOE, DOD, DHS, and emergency management communities.

A Dissertation Submitted to the Department of Meteorology in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.

Summer Semester, 2010.

April 29, 2010.

Particles, Plumes, Buoyant Jets, Convective, HIGRAD

Paul Ruscher, Professor Directing Dissertation; James B. Elsner, University Representative; Carol Anne Clayson, Committee Member; Henry E. Fuelberg, Committee Member; Guosheng Liu, Committee Member.

Advisors/Committee Members: Paul Ruscher (professor directing dissertation), James B. Elsner (university representative), Carol Anne Clayson (committee member), Henry E. Fuelberg (committee member), Guosheng Liu (committee member).

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A karst aquifer is a carbonate aquifer where groundwater flow dominantly occurs through bedding planes, fractures, conduits, and caves created by and/or enlarged by dissolution. Conventional groundwater modeling methods assume that groundwater flow can be described by Darcian principles where primary porosity (i.e. matrix porosity) and laminar flow are dominant in the aquifer. However, in karst aquifers this assumption is inapplicable due to the dual porosity present in karst aquifers. While Darcian principles may apply to the matrix portion of the karst aquifer, they often do not apply to flow through conduits, where flow velocities can be great enough to invalidate the applicability of Darcy's Law. Thus, different methodologies must be used to model groundwater flow in karst aquifers. MODFLOW-CFP is a relatively new modeling program which accounts for turbulent and laminar flow in pipe like karst caves. In this study the methodology of MODFLOW-CFP is compared to several other methods to evaluate the accuracy that CFP can achieve when modeling flow in karst conditions at a laboratory and sub-regional scale. This study also briefly evaluates the program MT3DMS, to test its abilities for modeling contaminant transport in a karst aquifer analog at a laboratory scale. Results at the laboratory scale indicate that CFP is more accurate when compared to simulated results generated by MODFLOW 2005, and performs better when compared to a Navier-Stokes finite element model developed by Hua (2009). At the sub-regional scale, CFP is less accurate than the traditional MODFLOW-2000 model when comparing peak flow conditions for a simulated storm event. However, for total simulated flow for the storm event, CFP produces more accurate results than MODFLOW-2000. Regarding transport, MT3DMS can adequately simulate transport within karst at a laboratory scale.

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.

Spring Semester, 2011.

March 18, 2011.

Bill X. Hu, Professor Directing Thesis; Ming Ye, Committee Member; Stephen Kish, Committee Member.

Advisors/Committee Members: Bill X. Hu (professor directing thesis), Ming Ye (committee member), Stephen Kish (committee member).

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A greatly expanded section of Holocene sediment was recovered at Site NBP0602-8 in the Firth of Tay near the tip of the West Antarctic Peninsula during the SHALDRIL II cruise aboard the R/V Nathaniel B. Palmer, 2006. Recovery in the four holes at this site was ~85%, with the exception of the uppermost eight meters of water saturated sediments. The next year the site was revisited during Cruise NBP0703 and a jumbo piston core (JPC 02) recovered sediment to 23 meters below seafloor to fill missing gaps in the upper section. Fossil diatoms have been proven to be highly useful in paleontological climate reconstruction. Therefore, this investigation is a down-core quantitative study of diatom assemblages from this Firth of Tay sequence to identify and constrain changes in paleoenvironmental events. The project provides evidence of an early deglaciation episode, the Mid-Holocene Climatic Optimum, and subsequent cooling and Neoglacial conditions that persist until the present. The Mid-Holocene Climatic Optimum delineated in this study correlates closely with the timing and duration of this event in Maxwell Bay, to the north. The same event is recorded in Palmer Deep on the opposite (west) side of the Antarctic Peninsula but with an earlier onset and longer duration. The Climatic Optimum recorded at the Firth of Tay is less pronounced than at the other two sites, however, due to the colder water stemming from the Weddell Sea Gyre.

A Thesis submitted to the Department of Geology in partial fulfillment of the requirements for the degree of Master of Science.

Spring Semester, 2010.

May 3, 2010.

Antarctic Peninsula, Firth of Tay Diatom, Mid-Holocene Climatic Optimum

Sherwood W. Wise, Professor Directing Thesis; Anthony J. Arnold, Committee Member; Joseph F. Donoghue, Committee Member.

Advisors/Committee Members: Sherwood W. Wise (professor directing thesis), Anthony J. Arnold (committee member), Joseph F. Donoghue (committee member).

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Past binary logistic regression (BLR) and perfect prognosis schemes have shown skill for predicting the probability of one or more cloud-to-ground (CG) lightning flashes for regions such as Florida. This study examines the ability of the BLR and perfect prog techniques to forecast only those flashes at the daily onset of warm season convective activity. A statistical model is developed for two domains in the western United States in the vicinities of Amarillo, Texas and Albuquerque, New Mexico, to predict the probability of one or more CG flashes during the 1800 UTC to 2100 UTC time window. Warm season convection in these locales is influenced by factors such as the Southwest Monsoon, drylines, and topography. Each domain consisted of a 28 × 26 grid at a 10-km resolution. One equation for each domain was developed using 10-year climatology and predictors from the North American Regional Reanalysis (NARR) dataset for the dependent period May through September of 1994 – 2004. In our perfect prog scheme, the reanalysis data were treated as observations. Forecasts were made for the 2005 warm season, and evaluated using the Brier Score, Brier Skill Score, and reliability diagrams. Due to the relative rarity of the event being forecast, forecast probabilities tended to be small, rarely exceeding the 30% range in the Amarillo domain and 70% (with a majority below 50%) in the Albuquerque domain. Both domains typically exhibited skill over climatology and good reliability for low forecast probabilities, which constituted a majority of the forecasts. Sample forecasts for both domains are examined. The Amarillo model demonstrated competent performance on 10 June 2005, but poor performance on 1 September 2005. The Albuquerque model performed well on 1 September 2005, but performed poorly on 17 July 2005. Despite the low magnitude of probabilities forecast, both models showed promise, commonly placing their relative maxima in the vicinity of the verifying initiating flashes, with some obvious exceptions.

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.

Summer Semester, 2011.

August 24, 2007.

Statistical Modeling, Forecasting, Lightning

Henry E. Fuelberg, Professor Directing Thesis; Jon Ahlquist, Committee Member; Paul Ruscher, Committee Member.

Advisors/Committee Members: Henry E. Fuelberg (professor directing thesis), Jon Ahlquist (committee member), Paul Ruscher (committee member).

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The variations in the sea breeze are examined both diurnally and interannually along the panhandle of Florida during the boreal summer season. A climatology of sea breeze cross sections is calculated eight times daily between the years 1979 and 2001 to examine diurnal differences. The cross sections are created using very high resolution dynamically downscaled analyses from the NCEP-DOE (R2) and the ECMWF ERA-40 for the southeast U.S. The high resolution downscaled product is validated with other independent observations to show fidelity. Results from these diurnal analyses show that the sea breeze and precipitation peak at 4:00 p.m. The interannual variability of the sea breeze is examined with respect to the Atlantic Warm Pool (AWP). Composites consisting of Climate Prediction Center (CPC) precipitation observations are created based on the size of the AWP. These composites show that the strongest low-frequency signal is a negative anomaly along the panhandle. Therefore, model composite cross sections are primarily along the 30.5°N latitude. The cause of the negative anomaly is related to the subtropical high, which undergoes an eastward shift and a decrease in intensity for large AWP years. These changes in the subtropical high lead to a more cyclonic large-scale low-level flow for large AWP years as Sverdrup vorticity balance indicates. This study finds that this synoptic flow pattern will suppress the sea breeze circulation and lessen precipitation amounts over the panhandle region.

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.

Summer Semester, 2011.

April 28, 2011.

Bermuda High, Atlantic Warm Pool, Sverdrup Vorticity Balance, interannual variations

Vasubandhu Misra, Professor Directing Thesis; James J. O’Brien, Professor Co-Directing Thesis; Henry Fuelberg, Committee Member; Mark Bourassa, Committee Member.

Advisors/Committee Members: Vasubandhu Misra (professor directing thesis), James J. O’Brien (professor co-directing thesis), Henry Fuelberg (committee member), Mark Bourassa (committee member).

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Ice and snow particles have a great, yet poorly understood impact on the Earth's climate system. One of the difficulties of studying snow particles is their irregular shape. While spheres and even oblate spheroids backscatter radiation in a consistent manner, irregularly shaped objects do not. Due to the complexities of snowflakes, they are often assumed to be spherical for both satellite retrieval and modeling purposes. This can introduce error in many studies. While there are several aggregate snowflake models in existence, many use spheres as a building block for the snowflake. This is inaccurate as most snowflakes are comprised of a combination of bullet rosettes, plates, columns, and dendritic snow crystals. Furthermore, most studies do not have constraints in place to make sure that snowflakes are of the correct size and density as observed from field studies. None of the theoretical models examined in this study analyze the single-scattering properties of the flakes. In order to improve upon previous models, this study creates an aggregate snowflake using 200 ìm and 400 ìm 6-bullet rosette crystals. These crystals and resultant flakes are required to follow established size-density relationships obtained from numerous field studies. In addition, the flakes must also be of similar fractal dimension determined from other case studies. The single-scattering properties of these flakes are then determined from the discrete dipole approximation.

A Thesis submitted to the Department of Meteorology in partial fulfillment of the requirements for the degree of Master of Science.

Summer Semester, 2010.

April 13, 2010.

dda, Extinction Coefficient, Scattering Coefficient, Absorption Coefficient

Guosheng Liu, Professor Directing Thesis; Robert G. Ellingson, Committee Member; Paul Ruscher, Committee Member.

Advisors/Committee Members: Guosheng Liu (professor directing thesis), Robert G. Ellingson (committee member), Paul Ruscher (committee member).

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

A Dissertation Submitted to the College of Arts and Sciences in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.

Spring Semester, 2011.

November 09, 2010.

Lightning, Severe Storms, Radar, NLDN, WDSS-II, GIS

Henry E. Fuelberg, Professor Directing Dissertation; J. Anthony Stallins, University Representative; Carol Ann Clayson, Committee Member; Robert E. Hart, Committee Member; Guosheng Liu, Committee Member.

Advisors/Committee Members: Henry E. Fuelberg (professor directing dissertation), J. Anthony Stallins (university representative), Carol Ann Clayson (committee member), Robert E. Hart (committee member), Guosheng Liu (committee member).

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This study uses the high-resolution infrared radiation AVHRR (Advanced Very High Resolution Radiometer)-only and microwave radiation AMSR (Advanced Microwave Scanning Radiometer)+AVHRR sea surface temperature (SST) datasets to analyze and compare non-Gaussian statistics and extreme events for SSTs. Since the primary difference between the two datasets is the lack of AVHRR data in regions of cloud cover, higher correlations between the datasets are expected in areas of low percent daily-averaged total cloud cover. These are regions where both sensors usually are capable of detecting SSTs and do not rely on the process of optimum interpolation to fill missing data. Probability density functions, skewness, kurtosis, autocorrelation time scale, and standard errors are used to reveal non-Gaussianity (i.e., statistically extreme events) in the datasets, while the correlation coefficient between the datasets is used to explore extreme events beyond a certain threshold. Non-Gaussianity is present in both SST datasets, and the highest correlations of extreme events between the datasets were within positive anomalies above a certain threshold for regions of low percent daily-averaged total cloud cover.

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, 2010.

August 3, 2010.

extreme events, non-Gaussian, skewness, kurtosis, SST, AVHRR, AMSR

Philip Sura, Professor Directing Thesis; Carol Anne Clayson, Committee Member; Sharon Nicholson, Committee Member.

Advisors/Committee Members: Philip Sura (professor directing thesis), Carol Anne Clayson (committee member), Sharon Nicholson (committee member).

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

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.

Spring Semester, 2011.

March 28, 2011.

Tropical Cyclones, Climatology, Reanalysis

Robert Hart, Professor Directing Thesis; Carol Anne Clayson, Committee Member; Henry Fuelberg, Committee Member.

Advisors/Committee Members: Robert Hart (professor directing thesis), Carol Anne Clayson (committee member), Henry Fuelberg (committee member).

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Warm seclusions are large midlatitude storms that have the potential to substantially influence the turbulent heat fluxes and global energy budget. These storms have not been previously investigated from an energy and flux perspective. They have large areas of strong surface winds and rapidly moving cold fronts, which are associated with large air-sea differences of temperature and humidity. These regions contain large air-sea fluxes of latent and sensible heat. Therefore, errors in model representation of warm seclusions may introduce significant bias and uncertainty to the energy budget. The turbulent heat fluxes associated with three specific warm seclusions in different ocean basins are examined through an intercomparison of satellite- derived flux data and numerically derived flux data. The satellite data includes the SeaFlux version 0.75 data derived from SSM/I (Special Sensor Microwave/Imager), and model-derived reanalysis data includes CFSR, ERA-Interim, MERRA, and NCEP-R2 reanalysis data sets. Latent and sensible heat fluxes are computed in a physically consistent manner though the use of a bulk flux parameterization A single warm seclusion, which typically lasts between three and seven days, is responsible for approximately one quarter of the total time-integrated monthly fluxes for the ocean basin containing the warm seclusion, depending on the storm and data set under consideration. The large area of extremely large fluxes is associated with the mature phase of the cyclone. Proper representation of these fluxes is critical to determining accurate monthly- averaged, basin-wide fluxes.

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.

Summer Semester, 2011.

March 29, 2011.

Satellite, Reanalysis, Air Sea Interaction, Turbulent Heat Fluxes, Intercomparison, Warm Seclusion

Mark A. Bourassa, Professor Directing Thesis; Carol Anne Clayson, Professor Co-Directing Thesis; Philip Sura, Committee Member.

Advisors/Committee Members: Mark A. Bourassa (professor directing thesis), Carol Anne Clayson (professor co-directing thesis), Philip Sura (committee member).

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Rapid intensity changes in hurricanes have been the focus of many publications. Understanding how and why these storms intensify has been the goal of many meteorologists over the last few years. This study explores the energetics of Psi-Chi interactions in modeled hurricanes of rapidly changing intensity. The energy exchanged within the storm as the flow changes from divergent to rotational is known as Psi-Chi interactions. Processes associated with latent heant and sensible heat exchanges are important when it comes to identifying changes in hurricane intensity. Understanding this interaction with the environment is crucial to understanding how the intensity changes. Model data derived from the fifth generation model from NCAR/Penn State known as the MM5 is used to calculate each term within the Psi-Chi equation. Each term is then calculated within the storm and its maximum values as well as location of maximum values within the storm are noted. The maximum value of each term and location of each term allows for an investigation of a connection between the energy exchange of the storm and its intensity. The maximum values of the terms of Psi-Chi interactions are also compared to the model intensity of each storm. Based on the comparison of model intensity and maximum term values there appears to be a strong relationship between the two (correlation values near r = 0.87), although further study is needed to determine if this simultaneous relationship can be extended to a lagged relationship to provide predictive value to forecasters.

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.

Summer Semester, 2011.

March 7, 2011.

Hurricane, Psi Chi, Intensity

T. N. Krishnamurti, Professor Directing Thesis; Robert E. Hart, Committee Member; Vasubandhu Misra, Committee Member.

Advisors/Committee Members: T. N. Krishnamurti (professor directing thesis), Robert E. Hart (committee member), Vasubandhu Misra (committee member).

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Submarine groundwater discharge (SGD) assessments conducted both in the laboratory and at a field site in the northeastern Gulf of Mexico, using a continuous-heat type automated seepage meter (seepmeter) have shown that the device has the potential of providing long-term, high-resolution measurements of SGD. The improvements on the device using a simple inexpensive laboratory set up, have shown that: (1) connecting an extension cable to the seepmeter has a negligible effect on its measuring capability and, (2) influence of very low temperature (≤ 3 ºC) on seepmeter measurements can be accounted for by conducting calibrations at such temperatures prior to field deployments and, (3) salinity had no significant effect on the performance of the seepmeter. Calibration results from fresh water and sea water showed close agreement at a 95% confidence level significance between the data sets from the two media (R2 = 0.98). The observed artifacts on seepmeter measurements associated with Bernoulli-induced flow, the vertically directed flow arising due to water movement across topographic features can significantly be reduced by burying (or submerging) the seepmeter to nearly the same level as the sediment topography. While the study revealed that in general wind speeds > 6 m/s were associated with enhanced SGD measurements in seepmeters with buried and unburied benthic chambers, the influence was greater in the unburied meters, and more pronounced for SGD rates 6 m/s were associated with enhanced SGD measurements in seepmeters with buried and unburied benthic chambers, the influence was greater in the unburied meters, and more pronounced for SGD rates Study of the Sarasota Bay (SB) system revealed SGD advection rates ranging from 0.7 to 24.0 cm/day, except for rare isolated hot spot occurrences where higher rates were observed. In general, SGD estimates were relatively higher in the middle and south regions (5.9 – 24.0 cm/day) compared to the north region (0.7 – 5.9 cm/day). Although no obvious seawater nutrient concentration trend was revealed, the average N/P ratio was higher in the north compared to the middle and south regions of the SB system. The importance of SGD was evident in that about 40% of the regional nutrient fluxes were observed in the north while ~ 60% occurred in the middle and south regions combined. The latter two regions also had the highest overall nutrient flux per water volume ratio, compared to the north region, thus making them potentially more vulnerable to eutrophic conditions. On average, we estimate about 27% of total dissolved N in the SB system was derived via SGD.

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.

Fall Semester, 2010.

August 26, 2010.

hydrology, Submarine groundwater discharge, groundwater, seepage meter, seepage meter artifacts, Florida, nutrients, nutrient fluxes, marine environment, nearshore, processes, measurements, coastal zone, Turkey…

Advisors/Committee Members: William C. Burnett (professor directing dissertation), Xiaolong Bill Hu (university representative), Jeffrey P. Chanton (committee member), William M. Landing (committee member), Joel E. Kostka (committee member).

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This study has evaluated an existing hybrid three-dimensional variational ensemble transform Kalman filter (3DVAR-ETKF) ensemble data assimilation system using the Weather Research and Forecasting (WRF) model in realistic numerical weather prediction experiments. The study was divided into three parts: Part one assessed the skill of the ETKF ensemble generation scheme with and without implicit mode error included in the ensemble. Part two assessed the benefit of including flow-dependent information into the hybrid cost function. Part three proposed an alternative to ETKF and tested its performance in cycling experiments. The ETKF perturbations as an ensemble-generation scheme performed well in single and multi-physics ensemble approaches. The multi-physics ETKF ensemble performed best maintaining the appropriate variance and dependence on covariance inflation. The multi-physics ETKF ensemble was characterized by larger (smaller) error growth (reduction) during the model integration than the single-physics ensemble. Using the ensemble mean as the first guess in the 3DVAR cost function significantly improved the skill of the analyses. Tuning the static 3DVAR background error covariances using the ETKF ensemble perturbations instead of time-lagged perturbations improved the skill of the deterministic and ensemble 3DVAR analyses as measured by 12- through 48-h deterministic forecast skill. Incorporating ensemble-based flow-dependent error covariances from limited 20-member ensembles into the hybrid cost function added skill to the analyses. This added skill was in addition to that achieved by using the ensemble mean as the first guess and using the tuned background error covariances. The greatest improvements in analysis skill were observed when a multi-physics ensemble was used to supply the error covariances to the hybrid cost function. Vertical localization added some skill to the analyzed wind speeds, mostly at longer lead times and when the localization length scale is less restrictive. The proposed hybrid Lanczos ensemble filter (HLEF) ensemble generation scheme was shown to be equivalent to the ETKF scheme when no inflation was applied and the HELF perturbations did not include the effect of covariance localizations or hybridization. Both vertical and horizontal covariance localization in the HLEF perturbations ameliorated the under estimation of analysis uncertainty. 10-day cycling experiments with inflated and localized HLEF perturbations required less than 30% of the magnitude of the inflation required by ETKF. Experiments that addressed the possibility of producing analysis perturbations that are consistent with the hybrid variational cost function produced encouraging results.

A Dissertation Submitted to the Department of Earth, Ocean and Atmospheric Sciences in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy.

Spring Semester, 2011.

March 28, 2011.

Physics Uncertainty, 3DVAR, Hybrid, Lanczos, ETKF, Ensemble Data Assimilation, Data Assimilation

Henry E.…

Advisors/Committee Members: Henry E. Fuelberg (professor directing dissertation), I. Michael Navon (university representative), Robert Hart (committee member), Jon E. Ahlquist (committee member), Xiang-Yu Huang (committee member), Guosheng Liu (committee member), P. Anil Rao (committee member).

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Numerical models for variable-density flow and solute transport (VDFST) are widely used to simulate seawater intrusion and related problems, including submarine groundwater discharge (SGD). The mathematical model for VDFST is a coupled nonlinear system written in state-space and time form, so the numerical discretization in time and space are usually required to be as fine as possible. As a result, such large space and time transient models are computationally very demanding, which is disadvantageous for state estimation, forward prediction or inverse calculation. The purpose of this research was to develop mathematical and numerical methods to simulate variable-density flow and salt transport via a model reduction technique called "proper orthogonal decomposition" (POD) for both linear and nonlinear models. It was showed that this method can generate representations of data that contain general information about the solution of the original partial differential equations. Data analysis using POD was conducted to extract dominant "model features" (basis functions) through singular value decomposition from experimental data or detailed simulations of high-dimensional systems (snapshots). These basis functions were then used in the Galerkin projection procedure that yielded low-dimensional reduced models. The original full numerical models were presented by the Galerkin finite-element method. The implementation of the POD reduced method was straightforward referring to the complex full model. The developed POD method was applied to solve two classic VDFST problems, the Henry problem and the Elder problem, to investigate the accuracy and efficiency of the POD method. The reduced model can reproduce and predict the full model results very accurately with much less computational time in comparison with the full model. It was showed that the accuracy and efficiency of the POD reduced model is mainly determined by the optimal selection of snapshots and POD bases.

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.

Fall Semester, 2010.

October 19, 2010.

Sigular Value Decomposition, Proper Orthogonal Decomposition, Variable-Density flow, Submarine Groundwater Discharge, Model Reduction, Galerkin Finite Element

Bill X. Hu, Professor Directing Dissertation; William C. Burnett, University Representative; Ming Ye, Committee Member; Joseph F. Donoghue, Committee Member; Jeff Chanton, Committee Member.

Advisors/Committee Members: Bill X. Hu (professor directing dissertation), William C. Burnett (university representative), Ming Ye (committee member), Joseph F. Donoghue (committee member), Jeff Chanton (committee member).

▼ A data assimilation method is developed to calibrate a heterogeneous hydraulic conductivity field conditioning on observation of a transient groundwater flow field or transient conservative solute transport field. An ensemble Kalman filter (EnKF) approach is used to update model parameters such as hydraulic conductivity and model variables such as hydraulic head or solute concentration using available data. A synthetic two-dimensional flow case is used to assess the capability of the EnKF method to calibrate a heterogeneous conductivity field by assimilating transient flow data from observation wells under different hydraulic boundary conditions. The study results indicate that the EnKF method will significantly improve the estimation of the hydraulic conductivity field by assimilating hydraulic head measurements and the hydraulic boundary condition will significantly affect the simulation results. The ensemble size should be 300 or larger for the numerical simulation in the study case. The number and the locations of the observation wells will significantly affect the hydraulic conductivity field calibration. Another synthetic case with the mixed Neumann/ Dirichlet boundary conditions is designed to investigate the capacity and effectiveness of a constrained EnKF by assimilating the solute concentration to identify a conductivity distribution. The study results indicate that the constrained EnKF method will significantly improve the estimation of the hydraulic conductivity field by assimilating solute concentration measurements. The larger area for the initial distribution of the solute concentration, the more observed data can be obtained, the better the inversed results. The number of the actual observation wells needed to calibrate the hydraulic conductivity field through the constrained EnKF method via assimilating the solute concentration is very small. The data assimilation method can produce useful results in the first five or seven time step assimilation. The simulated results by the data assimilation method are still very similar with different observation errors. Based on the problems of the filter divergence in the data assimilation application, the localized EnKF method is applied. The covariance inflation and localization schemes are used to the transient state groundwater water flow. The synthetic study case of the transient groundwater flow is the same as the research before, but the assumed real conductivity values are correlated. The simulations by the data assimilation with and without localized EnKF are compared. The hydraulic conductivity field can be updated efficiently by the localized EnKF, while it cannot be updated via just the EnKF. The covariance inflation and localization are found to efficiently solve the problem of the filter divergence. The ensemble size for the localized EnKF method is 100 and less than that only in the EnKF before, which reduce the computer cost. The correlation length is found to affect the simulation by the localized EnKF method much more than the localization… Advisors/Committee Members: Bill X. Hu (professor directing dissertation), I. Michael Navon (university representative), James F. Tull (committee member), Yang Wang (committee member), Ming Ye (committee member).

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Prior studies of the long-term temperature record in the Southeastern United States (SE US) mostly discuss the long-term cooling trend, and the inter-annual variability produced by the region's strong ties to El Niño Southern Oscillation (ENSO). An examination of long-term temperature records in the SE US show clear multi-decadal variations in temperature, with relative warm periods in the 1920's through the mid 1950's and a cool period in the late 1950's through the late 1990's. This substantial shift in multi-decadal variability is not well understood and has not been fully investigated. It appears to account for the long-term downward trend in temperatures. An accurate characterization of this variability could lead to improved interannual and long-term forecasts, which would be useful for agricultural planning, drought mitigation, water management, and preparation for extreme temperature events. Statistical methods are employed to determine the spatial coherence of the observed variability on seasonal time scales. The goal of this study is to characterize the nature of this variability through the analysis of National Weather Service Cooperative Observer Program (COOP) station data in Florida, Georgia, Alabama, North Carolina, and South Carolina. One finding is a shift in the temperature Probability Distribution Function (PDF) between warm regimes and cool regimes.

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.

Summer Semester, 2010.

July 2, 2010.

Meteorology, Climate Variability, Climate, Warm Regime, Cold Regime

Mark. A. Bourassa, Professor Directing Thesis; Eric P. Chassignet, Professor Directing Thesis; Philip Sura, Committee Member; David F. Zierden, Committee Member.

Advisors/Committee Members: Mark. A. Bourassa (professor directing thesis), Eric P. Chassignet (professor directing thesis), Philip Sura (committee member), David F. Zierden (committee member).

▼ Anthropogenic aerosols are known to alter clouds and their optical properties by serving as cloud condensation nuclei. An increase in aerosol concentration causing smaller but more cloud droplets for a fixed liquid water content, thereby resulting in an increased cloud optical thickness and increased reflectivity of solar insolation, is called the first aerosol indirect effect. This effect leads to radiative cooling of the Earth and has the potential to counteract the greenhouse effect to some extent. However, an adequate quantification of this process remains elusive and leaves many outstanding questions. Many studies have been undertaken to better understand the uncertainties in the aerosol indirect effect as the aerosol-cloud interactions are considered to be one of the most important and least known forcings in the climate system but the complexity of this problem seems to grow with each new study. The objective of this study is to investigate and determine the problems in estimating the aerosol first indirect effect. The most common approach to estimate the indirect effect is to take into account only one or two controlling parameters, and emphasizing a result of a particular process, with all other processes being held constant. This type of simple approach often fails to extract the real aerosol indirect effect since many influencing factors that contribute to the change of cloud optical properties are interrelated in the nature. Furthermore, an incomplete specification of physical processes involved and not considering them simultaneously will produce inaccurate estimate of aerosol indirect effect. Therefore, in this study we have developed a methodology to untangle the aerosol effects from the interrelated factors, and then using satellite data, performed a comprehensive analysis of the aerosol indirect effect due to warm clouds over two oceanic regions. In this relatively idealized framework, the following four parameters can simultaneously contribute to the aerosol-related cloud radiative forcing: the change in spectral shape of the size distribution of cloud droplets (dispersion effect), the change in cloud droplet number concentration (Twomey effect), the change in cloud adiabaticity, and the change in cloud geometric depth, with variations in aerosol concentration. Furthermore, we have compared two different meteorological regimes, one (USWC, Pacific U.S. west coastal region) dominated by mainly stratiform clouds and the other (INDO, Indian Ocean region) by convective clouds. A detailed comparison of the mechanisms of aerosol-cloud microphysics/dynamics interactions in the two regions with different cloud types enables us to understand the dependence of the contributing parameters on cloud types. Based on our framework and observational data primarily from satellite, our data analyses have resulted in the conclusion that of the four contributing factors, the number effect and cloud depth effects are the most important in both regions. Dispersion effect, even though it offsets the effect in increased… Advisors/Committee Members: Guosheng Liu (professor directing dissertation), Ruby Krishnamurti (university representative), Robert G. Ellingson (committee member), Paul H. Ruscher (committee member), Xiaolei Zou (committee member).

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Statistics of extreme events in weather and climate (e.g. rare floods or strong wind storms) are commonly based on the assumption of Gaussian statistics. Sixty-two years of National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP / NCAR) Reanalysis I data and thirty-one years of National Centers for Environmental Prediction / Department of Energy (NCEP / DOE) Reanalysis II data are analyzed to determine if this assumption is true. The mean and variance of several atmospheric variables are calculated. Furthermore, the higher statistical moments — skewness and kurtosis — are calculated for geopotential height, relative vorticity, and the meridional and zonal wind components. Zonal averages of these higher statistical moments are also analyzed. It is found that statistically significant deviations from Gaussianity are found for every variable in the atmosphere on the synoptic to global scales. This empirical analysis is linked to particular atmospheric phenomena such as tropical cyclones, sudden stratospheric warming events, and the concept of rectifica- tion. In essence, there are fundamental forcing asymmetries in the atmospheric equa- tions of motion that lead to the existence of non-Gaussian distributions. Additionally, the relationship between skewness and kurtosis and the existence of power-law tails in non-Gaussian systems is examined.

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, 2010.

August 24, 2010.

Extreme Events, Non-Gaussianity

Philip Sura, Professor Directing Thesis; Jon Ahlquist, Committee Member; Robert Hart, Committee Member.

Advisors/Committee Members: Philip Sura (professor directing thesis), Jon Ahlquist (committee member), Robert Hart (committee member).

▼ There are no IAEA-GNIP stations in Florida. In order to improve our understanding of the proxy climate records preserved in speleothems, tree rings and lake sediments and to explore the utility of stable oxygen and hydrogen isotopes in the investigation of the water cycle in North Florida, there was a need to establish rainwater sampling stations to fill a gap in the oxygen and hydrogen records of rainfall in North Florida. Rain samples collected from Tallahassee and Pensacola in North Florida were analyzed for stable oxygen and hydrogen isotopic ratios. The Tallahassee samples span a time period from May 2006 to January 2011 and the Pensacola samples were collected from November 2004 to January 2010. Water samples were also collected in late 2010 and early 2011 from two coastal lakes (Eastern Lake and Western Lake in Walton County) and two ponds (Pond 1 and Bluesink in Apalachicola National Forest) in North Florida for stable isotope analyses. The δ18O and δD values of rain samples all plot either on or close to the Global Meteoric Water Line (GMWL) on a δ18O vs δD plot while most of the lake/pond water samples plot below the GMWL indicating that the lake waters in those area have been significantly affected by evaporation. Stable isotopic ratios of the Tallahassee samples ranged from -13.6 to 0.4‰ for δ18O and -99.4 to -2.2‰ for δD values (n=43) while those of the Pensacola samples ranged from -16.0 to 1.5‰ for δ18O and -115.8 to 118.9‰ for δD (n=260). Lake waters yielded δ18O values ranging from -4.7 to 1.9‰ and δD from -31.8 to 14.2‰. Pensacola samples have weighted monthly mean δ18O and δD values that ranged from -7.3 to -1.5‰ and from -4.3 to -18.7‰, respectively. The annual weighted mean δ18O and δD values for Tallahassee for study period are -4.5 and -23.3‰ respectively and -4.3 and -18.7‰ for Pensacola. The average d-excess value is 14‰ for Tallahassee and 9‰ for Pensacola. There is a negative correlation between the precipitation amount and the stable isotopic ratios of preciptation during the study period in North Florida. However, the "amount effect" can only explain less than 20% of the variance in the δ18O values of precipitation likely due to variations in the source and history of atmosphric moisture. There is a weak (but not significant) positive correlation between the average air temperature and the stable isotopic compositions of precipitation, suggesting that temperature is not a major factor in controlling the stable isotopic composition of precipitaion in this area. In Talahassee, rain samples for winter months had δ18O values ranging from -5.3 to -2.6‰, δD values from -30 to -6.2‰, and d-excess from 9.7 to 18.8. During the summer season, rain in Tallahassee displayed a larger range of isotopic variation, with δ18O and δD values ranging from -13.6 to 0.4 and from -99.4 to -7.7‰, respectively, and d-excess ranging from -11.2 to 14.7. The larger isotopic variability observed in the summer is primarily due to tropical storms. Rain samples from Pensacola had slightly more enriched monthly mean δ18O… Advisors/Committee Members: Yang Wang (professor directing thesis), James Tull (committee member), Lynn Dudley (committee member), Yuch-Ping Hsieh (committee member).

▼ This study presents the first high-resolution long-term history of seawater lithium isotope ratio (δ7LiSW) reconstructed from analyses of chemically cleaned planktonic foraminifera. The lithium isotope ratio of seawater (δ7LiSW ~31.0‰) is at secular equilibrium with its input sources via chemical weathering of the silicate continents (δ7LiRiv ~23‰), hydrothermal weathering of seafloor silicate basalts (δ7LiHT ~5.6‰) and removal by reverse weathering of authigenic sediments and seafloor basalts (δ7LiSED ~15‰). The δ7LiSW preserved in marine calcitic planktonic foraminifera provides a unique time tracer of changes in the global silica cycle. The Cenozoic 7Li/6Li record of seawater was constructed by analyzing over 300 age and species overlapping foraminifera samples, including both individual species and 'reverse picked' bulk foraminifera samples, from eight DSP/ODP Sites (588, 757, 758, 926, 1262, 1263, 1265, and 1267) with existing high resolution strontium isotope record. To meet the analytical requirements of foraminiferal δ7Li analyses an improved quadrupole-ICP-MS method for 7Li/6Li determination with low total lithium consumption (<0.2 ng/quintuplicate analyses) and high isotope ratio precision (≤ ±0.8‰, 2σ) was developed. A refined single step ion-exchange chromatographic method for quantitative lithium seperation, characterized by low blanks (1.0 ± 0.5 pg-Li) and high column yields (>99.98%), was also developed. The effects of foraminifera cleaning on calcite bound lithium concentrations and isotopic compositions were evaluated. A new analytical ICP-MS method for simultaneous determination of lithium, magnesium, manganese, vanadium, strontium, and barium ratios to calcium in chemically cleaned planktonic foraminifera was also developed. The newly developed analytical method and the improved foraminiferal cleaning technique was applied to late Cretaceous and Cenozoic samples to investigate the correlation between lithium isotopic composition and their lithium, magnesium, and strontium concentrations of the calcite shell as a guide to the to better explain the δ7Li record of seawater. The 68 Ma history of δ7LiSW spanning Late Cretaceous to Holocene demonstrates that the δ7LiSW decreased sharply by ~5‰ at the Cretaceous-Tertiary boundary and during the rest of the Cenozoic δ7LiSW increased by 8-9‰ over the last 60 Ma. Unlike the 87Sr/86Sr and 187Os/186Os isotope history of seawater, the rise in δ7LiSW during Cenozoic is not monotonous in nature. Plateaus and quasi-linear increases in δ7LiSW punctuate the 8-9‰ rise in seawater δ7Li during the Cenozoic. The sharp drop in δ7LiSW across K-Pg boundary was probably due to rapid supply large masses of isotopically light lithium to seawater from the congruent weathering of freshly erupted continental flood basalts (CFB's of Deccan Traps). The 8-9‰ rise in δ7LiSW during the rest of the Cenozoic suggests that hydrothermal contribution of isotopically light lithium to seawater has decreased over the Cenozoic, whereas, both lithium flux (FRiv) and isotopic composition… Advisors/Committee Members: Philip N. Froelich (professor directing dissertation), Munir Humayun (university representative), Willium C. Burnett (committee member), Jeffery P. Chanton (committee member), Marcus Huettel (committee member).

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Traditionally, research on bulk electrical conductivity is focused on the subject of soil salinity effects. Herein, bulk electrical conductivity was used to investigate the transport processes of soil. Electrical conductivity indicates the ability of the material to carry the electrons. In soils, water content is the dominant factor controlling conductivity. In addition to water content, salinity, clay content and temperature are also important factors in determining bulk electrical conductivity. Bulk electrical conductivity ECa is composed of the electrical conductivity of the liquid phase and surface electrical conductivity. The concept of critical water content has been proposed by different scientists in different ways. Here the critical water content is defined as the water content when the system transits from disconnected water films to a network of connected water filled pores, the critical water content occurs, mass transport becomes significant and tortuosity decreases. This work investigates the potential of using bulk electrical conductivity ECa to determine the critical water content. We used a relatively uniform sand and clay-sand mixtures as the porous medium instead of a complex soil. A test cell was designed to collect the electrical conductivity data of soil at different water content and the Wenner-array method was used. The electrolyte concentrations used in the experiment were 0.01 M KCl, 0.05 M KCl and 0.10 M KCl. Both error calculation and duplicated experiment has been done to determine the precision of our measurements. A plot of ECa vs. volumetric water content (è) failed to prove the evidence of the critical water content. The data analysis then used a Formation factor, or F factor which is closely related to ECa as a basis. The Fc factor proposed by Low and the F factor proposed by Rhoades were compared and it was determined that Rhoads model was consistent with observed trends. The F factor showed a significant change as water content increased, and samples with more clay had the sudden decrement in F at the higher water contents. Tuller's pore-scale model failed to provide a conceptual model of the observed trends. The critical path analysis (CPA) model provided an explanation of the F factor change with è, The CPA model represents porous medium as a system of large pores and thin pores with larger pores connected by thin pores. At certain water content, there is a critical condition wherein a network of thin pores is filled, and at this critical condition, the larger pores are connected and then mass transport becomes significant and the F factor decreases. The CPA model not only described a progression that fits our F factor data well, suggesting that samples with more clay have more thin pores, so it reaches the critical condition at higher water content.

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, 2011.

March 30, 2011.

Formation Factor,…

Advisors/Committee Members: Lynn Dudley (professor directing thesis), Vincent Salters (committee member), Ming Ye (committee member), Gang Chen (committee member).

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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

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,…

Advisors/Committee Members: 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).

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Southern Alaska crustal exposures provide an excellent opportunity to study the growth of collisional continental margins through the processes of terrane accretion, magmatism, accretionary prism development, and subduction of oceanic spreading ridges. Kodiak Island is one of the world's best exposed accretionary complexes, and is characterized by transport along dominant large-magnitude strike-slip faults of west North America and South Alaska. In this study we focus on detrital zircon dating of the Kodiak accretionary complex on Kodiak Island Alaska. Accretionary complexes are an important fundamental element of convergent plate margins and are also important structures in continental crust formation. Their presence in the geologic record is an indicator of past subduction zones. Six graywacke detrital zircon samples from the Kodiak and the Ghost Rocks Formations were analyzed using U/Pb dating of single crystals via laser-ablation inductively coupled plasma mass spectroscopy. The maximum depositional age of the three major formations are as follow: Kodiak Formation 56.2-69.2 Ma, and Ghost Rock 58.5 Ma. The age for the small outcrop of Narrow Cape Formation is 54.1. Kodiak and Ghost Rock Formation detrital zircon age are consistent with fossil ages of these two formations, but the fossil content of Narrow Cape is younger than the detrital zircon age we measured for this formation. Some evidence in our data like resurrection of certain age zircon grains between the accreted sequences, age gaps between the accreted sequences, different rate of sedimentation and etc. are evidenc for episodical accretion in the complex and also displacement of the accreted units along the west North America and Alaska right lateral large magnitude strike slip faults.

A Thesis submitted to the Department of Earth, Ocean and Atmospheric Sciences in partial fulfillment of the requirements for the degree of Master of Science.

Summer Semester, 2011.

June 17, 2011.

detrital zircon dating, accretionary prism, Kodiak Island

David Farris, Professor Directing Thesis; James F. Tull, Committee Member; A. Leroy Odom, Committee Member.

Advisors/Committee Members: David Farris (professor directing thesis), James F. Tull (committee member), A. Leroy Odom (committee member).

▼ Despite the fact that latent heating in cloud systems drives many atmospheric circulations, including tropical cyclones, little is known of its magnitude and structure due in large part to inadequate observations. In this work, a reasonably high-resolution (2 km), four-dimensional airborne Doppler radar retrieval of the latent heat of condensation is presented for rapidly intensifying Hurricane Guillermo (1997). Several advancements in the retrieval algorithm are shown including: (1) analyzing the scheme within the dynamically consistent framework of a numerical model, (2) identifying algorithm sensitivities through the use of ancillary data sources and (3) developing a precipitation budget storage term parameterization. The determination of the saturation state is shown to be an important part of the algorithm for updrafts of ~ 5 m s-1 or less. The uncertainties in the magnitude of the retrieved heating are dominated by errors in the vertical velocity. Using a combination of error propagation and Monte Carlo uncertainty techniques, biases were found to be small, and randomly distributed errors in the heating magnitude were ~16 % for updrafts greater than 5 m s-1 and ~156 % for updrafts of 1 m s- 1. The impact of the retrievals is assessed by inserting the heating into realistic numerical simulations at 2 km resolution and comparing the generated wind structure to the Doppler radar observations of Guillermo. Results show that using the latent heat retrievals outperforms a simulation that relies on a state-of-the-art microphysics scheme (Reisner and Jeffery 2009), in terms of wind speed root-mean-square errors, explained variance and eye/eyewall structure. The incorrect transport of water vapor (a function of the sub-grid model and the numerical approximations to advection) and the restrictions on the magnitude of heat release that ensure the present model's stability are suggested as sources of error in the simulation without the retrievals. Motivated by the latent heat retrievals, the dynamics of vortex axisymmetrization from the perspective of thermal anomalies is investigated using an idealized, non-linear atmospheric model (HIGRAD). Attempts at reproducing the results of previous work (Nolan and Grasso 2003; NG03) revealed a discrepancy with the impacts of purely asymmetric forcing. While NG03 found that purely asymmetric heating led to a negligible, largely negative impact on the vortex intensification, in the present study the impacts of asymmetries are found to have an important, largely positive role. Absolute angular momentum budgets revealed that the essential difference between the present work and that of NG03 was the existence of a significant, axisymmetric secondary circulation in the basic-state vortex used in the HIGRAD simulations. This secondary circulation was larger than that present in NG03's simulations. The spin-up of the vortex caused by the asymmetric thermal anomalies was dominated by the axisymmetric fluxes of angular momentum at all times, indicating fundamentally different evolution of… Advisors/Committee Members: Mark Bourassa (professor directing dissertation), Michael Navon (university representative), Robert Hart (committee member), Ming Cai (committee member), Xiaolei Zou (committee member).