<p>AgNET is a weather network, which collects surface and subsurface meteorological data in North Carolina. Each AgNet weather station measures a variety of weather parameters such as air temperature, relative humidity, wind speed and direction, barometric pressure, solar radiation, photosynthetically active radiation, soil temperature, soil moisture and precipitation. The station summarizes the above parameters for every hour and stores them in its local memory. Currently the data collected over the entire day are then transferred to a central server through phone lines. The data collected at the central server are published on the Internet and disseminated by other means as well. The purpose of this thesis is to describe the modernization of the AgNet weather network by making the network conform to standards, implement a uniform sensor configuration and improve the methods of data acquisition, dissemination and display of weather data.Since phone-based communication is not economical for real time data transfers other techniques such as Radio Frequency (RF) communication and satellite based communication were evaluated. RF communication was the most promising communication technique. Since RF is limited by distance, a combination of RF and Internet was designed. In this type of communication, data are transmitted from the weather station and received by a base station that is on the Internet. The received data are then forwarded to a central server at the State Climate Office where they are archived and disseminated. A successful test was conducted as proof of concept between Lake Wheeler road Field laboratory site, Raleigh and Varsity Laboratory, NC State University.Since every system has inherent noise, data collected at each station have to go through different quality control algorithms to insure data quality. Different Quality Control (QC) algorithms were implemented which are discussed in the thesis.<P>

<p>INDEJE, MATAYO. Prediction and Numerical Simulation of the Regional Climate of Equatorial Eastern Africa. (Under the direction of Dr. Fredrick H. M. Semazzi.). The objective in this investigation was to provide a better understanding of the mechanisms and physical processes responsible for climate variability over the equatorial eastern Africa, and explore potential for short-term climate prediction. Both statistical and numerical methods have been employed in this research. Application of cluster analysis yields 8 and 9 homogeneous climatic zones respectively for the variability of the annual and seasonal rainfall. Regions that are prone to drought or floods during the different phases of El Niño-Southern Oscillation (ENSO) are delineated. Positive rainfall anomalies occur in much of the region during March-May (MAM) and October-December (OND) of the ENSO(0) years and negative anomalies dominate during the following ENSO(+1) years. These rainfall patterns are useful for short-term climate monitoring over the region. The relationship between the Quasi-Biennial Oscillation (QBO) in the lower stratospheric zonal winds and the long-rains of MAM is more significant in lagged than in simultaneous, with the most distinct relationships occurring over the western parts of the region. The QBO-index explains about 36% of the seasonal rainfall variance. There is a 60/63 percent likelihood for the occurrence of above/below normal rainfall during the westerly/easterly phase of the QBO-index. The NCAR Regional Climate Model (RegCM2) simulations have demonstrated the added value of the nesting approach in improving regional climate simulations. The model reproduces the observed characteristics of the Turkana low-level jet. The study has shown the importance of orographic forcing, the large-scale background monsoon flow and depth of the channel in the development and maintenance of the jet. Thermal and frictional forcing play equivalent roles as that of the large-scale winds in the formation of the jet. The identified regions of strong winds associated with the jet are important to the safety in the aviation industry and are also potential for alternative renewable energy resources in the form of wind energy. Large-scale orography is the most important factor. Divergence and anticyclonic vorticity partly explains the observed split in the jet cores. The dynamics of the flow in the channel and the dry conditions observed over the wider part of the valley is in partly explained by the Bernoulli theorem as applied to barotropic steady and non-viscous flows. Air-sea interaction phenomenon over the Indian Ocean, and the latitudinal location and intensity of the large-scale Walker and Hadley circulations are the main physical mechanisms responsible for the climate variability over the region during the wet and dry years. Abundant rainfall is associated with the presence of a midtropospheric cyclonic wind shear across the equator, and a negative vertical wind shear. Likewise, dry conditions are associated with the presence a strong westerly/southerly wind anomaly that occurs throughout the troposphere. Short-term climate prediction models developed in this study are capable of skillfully reproducing the space-time evolutions and distribution of the seasonal rainfall over the region, and specifically the observed floods that occurred during the 1997 ENSO year. Preliminary application of the RegCM2 in the prognostic mode successfully produces a 3-months projection of the extreme seasonal anomalies associated with the 1997 ENSO event. These models can be exploited further in operational short-term climate prediction over equatorial eastern Africa.<P>

<p>SONG, YI. A Numerical Modeling Study of the Coupled Variability of Lake Victoria in Eastern Africa and the Regional Climate. (Under the direction of Dr. Fredrick H. M. Semazzi.). The objective of this investigation was to investigate and study the coupled atmosphere-lake climate system over the Lake Victoria basin, and determine the corresponding physical mechanisms that are involved. The primary research vehicle for the investigation is a fully coupled model of the regional climate of Eastern Africa and Lake Victoria which has been developed and applied in this study. The atmospheric component of the model is the NCAR Regional Climate Model (RegCM2). The lake component of the model is based on the Princeton Ocean Model (POM) configured for Lake Victoria by replacing the open boundaries in the standard version of the model with a closed coastline and adopting the bythemetry of Lake Victoria. The horizontal resolution is 20 km for both the atmosphere and lake model components.The results show that the bythemetry and geometry of the lake play a fundamental role in determining the climatology of Lake Victoria. There exists Kelvin-like waves in the thermocline trapped along the coast and they propagate clockwise around Lake Victoria with periodicity of about 30 days. The oscillations entirely disappear in the case of the isothermal conditions. The 3-dimensional model produces a surface temperature pattern indicative of horizontal lake water mixing associated with the horizontal spiral pattern that is not present in the 1-dimensional model. Preliminary comparison of the coupled RegCM2-POM model simulation results with the observations indicates that the model produces more realistic lake surface temperatures (LST) and rainfall over and around the lake than the standard version of RegCM2 in which a simple one dimensional thermal diffusion lake model is used. Over Eastern Africa, the regional climate variability is significantly influenced by the circulation over the Lake Victoria basin. Moisture advection contribution is important but secondary to evaporation in explaining the heavy rainfall over the lake. The interaction between the lake-land breeze and the prevailing northeasterly flow accounts for the asymmetry in the distribution of the diurnal rainfall variations and the southwestward movement of the dominant bands of divergence/convergence. During the 1982 El Nino when the averaged LST over the lake was higher than that during the normal year, the LST gradient was weakened along the SW-NE axis over the lake by the strong lake circulation. This results in LST distribution whereby the southwestern region of the lake is cooled while the region of maximum LST moves to the central-eastern region of the lake from the southwestern region of the lake. The net change in rainfall distribution over the lake during the 1982 El Nino is a combination of the effect associated with the large-scale convergence pattern and the meso-scale climate changes associated with the shift of the region of maximum rainfall toward the central-eastern part of the lake from the western part of the lake in response to the LST redistribution. Conversely, the weaker lake circulation enhances the LST gradient over the western part of the lake, especially over the northwestern region, and the rainfall maxima is still found over the northwestern sector of the lake. Therefore, the hydrodynamics of the lake play an important role in determining the coupled variability of the lake circulation and the lake basin-wide climatic conditions. This outcome based on the use of the coupled 3-dimensional lake model is not reproducible from the corresponding simulations based on the coupled 1-dimensional lake model. It is therefore apparent, that neglecting the lake's hydrodynamics and basing the lake model only on thermodynamical considerations deprives the coupled regional climate model of the ability to transport heat efficiently within the lake and thereby degrades the simulation of the climate downstream over the rest of the lake and the surrounding regions. The potential climate change resulting from total clearing of the tropical rain forests in Africa was also investigated by the standard version of the NCAR CCM3 global climate model. Over Eastern and Western Africa the impact of deforestation is primarily characterized by reduction in rainfall, however the CCM3 resolution of T42 which we have adopted may not be adequate to resolve the large contrasts in terrain and vegetation types. A striking result is that the strong remote response of the Southern Africa region to deforestation over Central Africa. This may be attributed to the role of the trapped large amplitude Rossby waves which transmit the response signal a long distance away from the source region. Based on the present results we infer that, the downscaling would be highly beneficial not only for the immediate region of Eastern and Central Africa where significant removal of tropical forest vegetation cover could occur in the coming decades, but also for the region further south to infer the projected detailed response of the Southern Africa region to remote deforestation effects.<P>

<p>Large-eddy simulation (LES) is a very useful tool in computationalfluid dynamics. The LES model allows one to solve a filtered set of theNavier-Stokes equations, thereby explicitly resolving scales of motionlarger than the discretization or grid size. Those motions smaller thanthe grid size are parameterized using a so-called subgrid scale model.<p>In this series of papers, we will use the TASS LES model, originallya cloud model, which has been modified to simulate planetary boundarylayer turbulence. We will first introduce the LES model and a newgrid-nesting method for the LES. Then we will present simulations ofthe convective planetary boundary layer, and then use the LES to studythe decay of convective planetary boundary layer turbulence to a stablystratified state.<p>The LES model has been modified to include a grid nesting capability.Grid meshes of higher resolution may be embedded within the LES enablingone to resolve smaller scales of motion (turbulence) than would bepossible by using a single grid mesh. The grid nesting methodology isdescribed in detail in Chapter 2.<p>In Chapter 3, the nested-grid LES will be applied to thesimulation of the convective planetary boundary layer. We will usea total of three grid meshes to increase the resolution in the surfacelayer, allowing a detailed analysis of the turbulence near the surface ofthe earth.<p>In Chapter 4, we will focus on applying Rayleigh Benardconvection criteria, using a linearized perturbation method,to the surface layer of a CBL produced by large-eddy simulation.Similarities and differences will be discussed between the LESproduced surface layer and classical Rayleigh-Benard convection theory.<p>In Chapter 5, using a large-eddy simulation model, we willexamine in detail the turbulent kinetic energy (TKE) budget during theevening transition. The simulation will be performed in order to compareto observations gathered at the Dallas-Fort Worth International Airport,Fort-Worth, TX. during September and October 1997.<p>In Chapter 6 the decay of planetary boundary layerturbulence during the evening transition will be studied. In previousstudies of the decay of turbulence, the effects of mean winds and shearsdue to pressure gradient on the turbulence decay was not considered.We propose to examine the effects of increasing geostrophic wind onthe convective boundary layer and its transition or decay to a stablecondition. Finally, the overall conclusions of each chapter will bepresented.<P>

<p>Mesoscale processes, dictated by surface characteristics, play adominant role in the development of the planetary boundary layer (PBL)structure and the formation of convection. The effect of mesoscale processeson the boundary layer structure also has significant implications in theunderstanding of circulation patterns and regional scale predictability. Largegeographical variability in North Carolina (NC) provides a wide variety ofweather events and climatological regimes.There are many challenges for numerical modeling in NC due to theheterogeneity in topography, land use, and soil type, presence of the oceanand the Gulf Stream. These heterogeneous attributes feature an excellentlocation for simulations and validation of the MM5 numerical modeling systemwith observations of high spatial and temporal resolution.MM5 is utilized for a non-precipitation case and a convective caseincluding precipitation with a 5-km domain centered over the Carolinas.Model integration is for 72 hours from 0000Z August 15, 2000 to 0000ZAugust 18, 2000. Simulated hourly surface and sub-surface values areevaluated against in-situ surface observations. These simulations consist ofreal case studies involving MM5 Version 3 with the MRF PBL schemecoupled to the Oregon State University (OSU) land surface model (LSM).The OSU LSM uses 1 km resolution land-use and soil data as input into MM5for capturing the dynamics of land-surface forcing.The acquisition and combination of different agro-meteorological dataacross NC provides high-resolution observations used for validation atmultiple model grid points. For the case studies, these data incorporate hourlyobservation sites throughout North Carolina including 19 ASOS (AutomatedSurface Observing Sites / owned and operated by the NWS and FAA) sitesand 15 ECONet (Environmental and Climate Observing Network: maintainedby State Climate Office of North Carolina) sites. Multiple parameterscompared and investigated using this network of observations include:ECONet: Air Temperature (2m), Relative Humidity (2m), Wind Speed (10m),Wind Direction (10m), Soil Temperature (10 cm), Soil Moisture (10cm), HourlyPrecipitation rate; ASOS: Air Temperature (2m), Dewpoint (2m), Wind Speed(10m), Wind Direction (10m), Hourly Precipitation, Weather Conditions, andCloud Layers.The approach involves examination of simulated horizontal and verticalwind patterns across the coast, piedmont, and mountainous regions in NorthCarolina. These simulated wind fields are used to investigate local land-seainteractions near the coast, effects of land surface processes in the piedmont,and pollution transport potential over complex terrain in the mountains of North Carolina. Precipitation patterns generated by the model are alsocompared with daily observations of precipitation amounts in conjunction withthe hourly stations across the central portion of the 5 km domain, particularlyNorth and South Carolina.Following a graphical comparison of 2D and 3D fields, statisticalmethods are applied to provide quantitative relationships for errors and biasesin the simulations. The analyses give additional insight into modelperformance. This is especially important when validating complex andcomprehensive interactions and processes that occur in North Carolina.Statistical measures used include: absolute correlation, root mean squareerror (RMSE), bias, normalized mean square error (NMSE), weightednormalized mean square error of the normalized ratios (WNNR), normalizedmean square error of the distribution of the normalized ratios (NNR), and theindex of agreement.Diurnal variation is handled well by the model indicating that thethermodynamic structure of the atmosphere is well simulated. Nocturnalboundary layer processes are poorly simulated, particularly in western NC,and heterogeneous surface features have significant effects on regional scaleprocesses including boundary layer structure and precipitation patterns.Model performance degrades over regions with complex terrain signifying thatmore observations are needed to develop regionally consistent flow patterns.Precipitation patterns are simulated with a fair amount of accuracy whenincluding the Kain-Fritsch cumulus parameterization scheme.<P>

<p>A male-focused size-selective fishing pressure has the potential to reduce the average size of the males in the population, reduce the density of males in the population, and/or raise the sex ratio of females to males. All of these may affect the mating dynamics of the population by reducing the amount of sperm that males provide to females and decreasing the number of males available for copulation. I used three different approaches to investigate the effect of the fishery on the population. First I collected paired and unpaired crabs from the field to investigate crab size and seminal stores in nature. This approach substantiated that male blue crabs subjected to heavier fishing pressure are smaller, and that smaller males pass less sperm and accessory fluid to females. It also demonstrated that although the most depleted males in the population are not mating, some that continue to form pre-copulatory pairs are as sperm depleted as males that had just completed copulation.My second approach involved the use of biotelemetry to monitor mating behaviors in the field. Tracked males demonstrated a proportionately greater amount of pairing behavior than tracked prepubertal females, which is consistent with expectations of crab behavior in a population with a female-biased Operational Sex Ratio. My third approach was to examine a long-term trawl data set for trends over time. A decline in the average size of mature males (carapace width >110 mm) and an increase in the operational sex ratio of pre-pubertal females to mature males (carapace width >110 mm) and pre-pubertal females to legally fished males (carapace width >127 mm) were found at one of the four trawl locations. The observed trends in size and sex ratio at that trawl location are as would be expected in a population where an increasingly intense fishery has been removing large males. Analysis of seminal stores in conjunction with the crab behaviors and population trends provides evidence that the fishery is in fact having a detrimental affect on the reproductive potential of the blue crab populatio<P>

<p>Boundary layer processes are the dominating factors in the diffusion and transport of pollutants. Air pollution dispersion is known to be controlled by several boundary layer factors. Eddy diffusion, described by the amount of turbulent kinetic energy, is the main influence on how quickly a parcel of polluted air expands and boundary layer depth determines the extent of vertical mixing potential. This thesis explores the influence that mesoscale surface related features have on the boundary layer meteorology and air pollution dispersion through a combination of numerical model simulations and observations. Mesoscale processes including sea breeze and land breeze circulations, vegetation and soil type gradient induced circulations, urban heat island and terrain modified flows are addressed in this research through the use of various numerical simulations. Surface based observations from a meso-network and ground based remote sensing observations using two SODARs are examined. These observations are also utilized for model validation.<p>An observational analysis of 10 m micrometeorological tower measurements and collocated SODAR measurements is conducted for two different boundary layer events, which correspond to near neutral and convective conditions. SODAR data analysis of reflectivity and wind speed profiles is presented along with tower measurements of wind speed/direction (at 2 m, 5 m and 10 m levels) and the temperature difference between 10 m and 2 m. The analysis indicated dramatically different boundary layer structures during these events.<p>The near-neutral case shows that the boundary layer properties remained relatively constant during the 24-hour period, as indicated by the SODAR reflectivity that consisted of homogeneous echoes up to a height of about 100 m. The static stability, implied by the observed 10 m - 2 m temperature difference (ÄT10m-2m), supports a neutral, well-mixed boundary layer. The wind speed profile indicated time dependent fluctuations in magnitude associated with shear induced boundary layer eddies.<p>The convective case shows a rapidly increasing boundary layer during the early morning, just after sunrise. Strong fluctuating periods of high reflectivity during the day allude to convective boundary layer thermals. At the same time, near surface temperature gradient (ÄT10m-2m) shows strong buoyant instability. The overall convective pattern and associated boundary layer momentum is much different than that of the neutral case. <p>Numerical simulations, using the Advance Regional Prediction System (ARPS) includes an idealized tropical seabreeze simulation over India, a regional scale simulation over eastern North Carolina and a city scale simulation over Raleigh, North Carolina. Using both the seabreeze and city scale meteorological simulations, coupled ARPS-CALPUFF dispersion simulations are conducted to investigate the influence of the boundary layer meteorology on dispersion patterns.<p>The 5 km resolution seabreeze simulation shows that the boundary layer properties are distinctly different across a region that is affected by seabreeze circulations. The dispersion experiment from a point source near the coastline indicated that the seabreeze has a very noticeable effect on atmospheric dispersion overland. Higher surface concentrations are modeled during the seabreeze episode and the post seabreeze period later in the evening.<p>The regional numerical simulation (6 km grid spacing) over eastern North Carolina combined several interesting boundary layer scenarios. The typically warmer Sandhills region and some of the larger urban centers are simulated as warmer surfaces. Turbulence is also higher over these warmer locations. Landuse is shown to have a definite impact on the degree of simulated turbulence as well as the boundary layer height. <p>The high-resolution atmospheric simulation conducted over Raleigh, North Carolina is for the same case presented by the regional simulation. The 1 km model forecast shows large distinctions within the microscale boundary layer structure over the city scale domain. The boundary layer variations are directly related to the landuse parameterization. During the night, the model is sensitive to terrain variations. Over the more elevated areas the wind speed was overall higher, while noticeably weaker over low-lying areas. A simulated down slope flow at night is detected and associated temperatures are less in the low-lying areas. The data from both SODARs compares well with the simulated profiles. <p>Dispersion patterns utilizing the high-resolution meteorology are influenced by the landuse in several respects. The 1 km ARPS simulation showed microscale convergence zones develop along strong surface temperature and sensible heat flux gradients, which are mostly a result of vegetation differences between the urban areas in/around Raleigh and surrounding rural areas. In the dispersion simulation, these convergence zones are directly related to higher surface concentrations. <p>The elevation is shown to influence the wind field at night, therefore modifying the concentrations field. More elevated areas, specifically the higher north-south ridge in the western part of the domain is associated with slightly stronger wind at night and therefore lower concentrations. The lower lying areas are more stable as a cooler slope flow is established at night. This drainage flow allows pollutants to collect over some of the highly populated suburbs around Raleigh.<P>

<p>PENG, MACHUAN. A numerical modeling study of the hydrodynamics of the Croatan-Albemarle-Pamlico Estuary System, North Carolina. (Under the direction of Lian Xieand Frederick Bingham)Numerical studies in the Croatan-Albemarle-Pamlico Estuary System (CAPES),are urgently needed for water quality control, environment protection and disastermitigation. In this study, a three-dimensional primitive equation hydrostatic model withhigh horizontal resolution is configured for the CAPES and its adjacent shelf toinvestigate barotropic/baroclinic wind driven circulation and sea level changes, riverdischarge induced flow, barotropic M2 tide, tidal current and tide-residual current. A newinundation/drying scheme is developed to allow the water-land boundary in the model tomove for simulating hurricane-induced coastal flooding and drying. This inundationalgorithm is based on the sea surface height relative to the adjacent topography, as well asthe distance traveled by the coastal interface, which is determined by the current speedimmediately seaward of the sea-land boundary.The main conclusions of this study are summarized below: (1) The verticalstructure of the wind driven circulation is more complicated in the coastal regions than inthe open area. On the open sea it follows a frictional Ekman equilibrium. (2) Thebaroclinic wind-driven current in the CAPES is over 40 cm/s in some regions due to greatvariations of the salinity distribution. (3) Stream flow nudging is a better method forspecifying the flux boundary condition near a river mouth than the barotropic-flowmethod in simulating river discharge induced flow. In annual mean case, such flow canbe ignored for its contribution to the coastal circulation, however, it could not be ignoredin flood cases. (4) M2 tide is much higher near the coast than inside the CAPES, but M2tidal currents in some regions inside Pamlico Sound can be greater than outside. Therelatively small M2 tide-induced residual current is stable and may have potential effectson long-term cross shelf transport. (5) Mass conservation must be considered in a closedor near closed estuary region when the inundation process is studied, and surface ratherthan vertically averaged current speed should be taken as the inundation speed.<P>

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Atmospheric Sciences" Title from author supplied metadata (automated record created on Sep. 15, 2006.) Vita. Abstract. Includes bibliographical references.

Thesis (Ph. D.)--Texas A&M University, 2005. / "Major Subject: Atmospheric Sciences" Title from author supplied metadata (automated record created on Sep. 15, 2006.) Vita. Abstract. Includes bibliographical references.