Small watershed budget studies are a major research tool in hydrology, ecology, and geochemistry. Most watershed hydrology and geochemistry studies attempt to avoid sites with groundwater seepage beneath topographic divides, known as interbasin groundwater transfer (IGT), due to the difficulty in quantifying it. However, IGT is an important and relatively common hydrological process that merits study. This project identified and quantified IGT by making detailed physical and chemical measurements in two adjacent lowland rainforest watersheds in Costa Rica: the Arboleda watershed, which receives IGT, and the Taconazo watershed, which is not affected by IGT. Physical hydrologic data allowed total IGT (mm/year) to be quantified in the context of water budgets for the watersheds, and the combination of physical and chemical data together allowed the IGT to be quantitatively separated into two components (high-solute bedrock groundwater and low-solute local water). Physical measurements of change in groundwater storage using piezometers, rainfall using a tipping bucket rain gauge, and stream discharge using V-notch weirs were made for four consecutive budget years. Major ion concentrations were measured in bulk rainfall samples, streamwater samples, and groundwater samples. The physical and chemical data were used to calculate annual water and chemical (Cl, SO4, Na, K, Mg, Ca) budgets for the two study watersheds. The watersheds had equal annual rainfall and ET (averaging 4,973 mm/yr and 2,107 mm/yr, respectively), but the Arboleda also had additional large water inputs by IGT (averaging about 4,367 mm/yr from bedrock groundwater and 5,590 mm/yr from local water). IGT to the Taconazo (all local water) was negligible (328 mm/yr). IGT of bedrock groundwater was mainly responsible for the Arboleda watershed receiving 18 times more Cl, 11 times more SO4, 36 times more Na, 54 times more K, 220 times more Mg, and 71 times more Ca input than the Taconazo watershed. Total solute input to the Arboleda watershed is dominated by bedrock groundwater, which accounts for an average of 84 percent (SO4) to 99 percent (Mg) of total solute input as compared with the Taconazo watershed where total solute input is controlled by rainfall accounting for on average of 77 percent (Mg) to 91 percent (SO4) of total solute input. The Arboleda watershed was in a steady state condition (i.e., the difference between inputs and outputs was within the range of uncertainty) for each solute during the 12/00-11/01 and 12/02-11/02 budget years, as was the Taconazo for Na and Ca in both budget years and Cl in the second budget year. The Taconazo chemical budgets showed an excess of SO4 inputs over outputs (+88 mol/ha and +115 mol/ha), a net loss of K (-165 mol/ha and -162 mol/ha), and a net loss of Mg (-256 mol/ha and -330 mol/ha). Traditionally, most watershed budget studies are conducted on the assumption that the watershed is ?tight?; however, the results of this study clearly indicate that caution should be used in making such an assumption. Results also suggest a linkage between deep groundwater systems and lowland rainforest may be important to watershed science, water quantity and quality, water management, and conservation of lowland rainforest ecosystems.

A habitat corridor is a landscape feature that is hypothesized to promote dispersal between habitat patches that would otherwise be isolated, and promote population persistence. Habitat corridors have not been widely explored in marine and estuarine systems. We used artificial seagrass units (ASUs) placed on unstructured sediment in Middle Marsh and Drum Shoals, Back and Bogue Sounds, North Carolina to create seagrass patches (1m2 and 4m2) separated by bare sediment or connected by additional ASUs, which made up a habitat corridor. We assessed the interactive effects of habitat corridor (presence or absence) and interpatch distance (5m or 10m), as well as the ratio of corridor width to patch width upon dispersal of grass shrimp, Palaemonetes sp., and bay scallops, Argopecten irradians in seagrass. We conducted mark-recapture experiments where marked grass shrimp or bay scallops were placed in one patch from each treatment (donor patch). Regardless of the presence of a habitat corridor, interpatch distance, or ratio of corridor width to patch width, dispersal between seagrass patches for grass shrimp and bay scallops did not significantly vary. There was, however, a significant site effect with the number of scallops successfully dispersing between seagrass patches significantly higher at Drum Shoals than at Middle Marsh. The small spatial scales of this study and the perception of a homogeneous environment may explain the lack of a dispersal response by grass shrimp. Site-specific differences in bay scallop dispersal may have been due to varying flow at the two study sites. Tethering experiments were conducted concurrently with dispersal experiments to assess the interactive effects of habitat corridor and interpatch distance, as well as perimeter to area ratio, on predation-induced mortality of bay scallops. Habitat corridor, interpatch distance or perimeter to area ratio did not significantly influence predation-induced mortality of scallops; however, there was a significant site by interpatch distance interaction. Predation rates were greater in patches separated by 10m at Middle Marsh than at Drum Shoals, whereas predation was greater in patches separated by 5m at Drum Shoals than at Middle Marsh. The lack of predation response to habitat corridors may have been due to a prey refuge in size (the scallops used in this study were relatively large, 35mm-50mm), or relatively low replication (N = 5) or another biotic or environmental factor not measured during this study. Colonization experiments were conducted to assess the interactive effects of habitat corridor and interpatch distance upon the colonization of estuarine macrofauna in seagrass. Neither mean density nor species diversity of estuarine macrofauna, nor mean density of individual taxonomic groups was significantly influenced by the presence of habitat corridors or by interpatch distance. Mean densities of slow-, intermediate-, and rapid-level dispersers were also not significantly influenced by the presence of habitat corridors or interpatch distance. The lack of community-level response may be explained by the interaction of hydrodynamics and its influence on the perception of a homogeneous or heterogeneous environment by dispersing organisms. Although habitat corridors may promote animal movement between habitat patches in terrestrial systems and for certain marine predators, the results from the present study do not confirm that habitat corridors are used by estuarine macrofauna for dispersal or colonization at relatively small spatial (10s of m) and temporal (hours to one month) scales. The coupled effects of hydrodynamics and habitat use should be considered when investigating distribution and abundance patterns of organisms with different dispersal abilities.

Eutrophication is increasing in estuaries as a result of anthropogenic activity along the land-sea margin. Human activities contribute large amounts of nitrogen and carbon compounds to watersheds, resulting in changes in resource availability through alteration of biogeochemical cycles. Although the effects of poor water quality on lower trophic level biota is well understood, the impact of nutrient waste on upper trophic levels, such as blue crabs (<I>Callinectes</I> <I>sapidus</I>), has not been well studied. Stable nitrogen (δ¹⁵N) and carbon (δ¹³C) isotope ratios can provide time and space integrated information about feeding relationships and energy flow through food webs. An isotopic comparison of the trophic structure of two North Carolina estuaries was undertaken to understand the impacts of anthropogenic runoff on blue crab tissue enrichment and feeding interactions. This study examined isotopic signatures of primary producers, as well as blue crab and their bivalve prey (<I>Rangia</I> <I>cuneata</I> & <I>Corbicula</I> <I>fluminea</I>) as indicators of potential changes in food web relationships in response to eutrophication. The Neuse River Estuary is an "impacted" system that experiences high nitrogen loading and drains areas of urban development, row crop agriculture, and concentrated animal operations. The Alligator River Estuary by comparison, is designated as a "less-impacted" system in this study. The Alligator River Estuary is classified as having "Outstanding Resource Waters" and low nutrient loading. In each estuary, samples were collected in the upper, middle and lower regions of the river. Bivalves collected from the Neuse River Estuary yielded a significant difference (p<0.0001) in mean nitrogen isotopic composition of tissue (10.4? ± 0.82; N=66) compared to the bivalves collected from the Alligator River Estuary (6.4? ± 0.63; N=45). Similarly, the Neuse River Estuary blue crabs had a mean nitrogen isotopic composition of 11.41? (± 1.3, N=77), which was significantly different (p<0.001) than the less-impacted Alligator River blue crabs (9.65? ± 0.6; N=77). The mean nitrogen isotopic ratios between blue crabs and bivalves were significantly different (p<0.0001) in the Neuse (1.01 ? ± 0.13) compared to the Alligator River Estuaries (3.2 ? ± 0.1). Linear regression analyses showed a significant inverse relationship between δ¹⁵N values of blue crab tissue and water quality for the Neuse River Estuary (R² = 0.7; p= 0.01). A generalized linear model was conducted using blue crab tissue δ¹⁵N as the dependent variable and river estuary as the independent variable of interest. This analysis showed a significant difference (p<0.0001) between rivers controlling for size, site, and the river by site interaction. The results of this study indicate that 1) a relationship exists between the uptake of anthropogenic nutrients by primary producers and the subsequent energy transfer to estuarine consumers, represented by δ¹⁵N and δ¹³C ratios, in two North Carolina estuaries; and 2) an inverse relationship exists between blue crab tissue enrichment and water quality in an impacted estuary.

Aerosols present in the Earth?s atmosphere play a crucial role in global meteorological conditions. If there is a larger concentration of aerosols then there may be a resulting variance in the weather and climate. One particular aerosol, which was measured and observed for this study, is black carbon. The presence of black carbon concentrations could result in a variance of certain weather variables at any given location. Black carbon aerosols absorb incoming solar radiation, which can impact the vertical temperature profile. A comparison of results can be made between weather and climate conditions in which a significant amount of black carbon is present, and other conditions with minimal amounts of black carbon in the troposphere. The observed data analyzed is from the Lake Wheeler site, a semi-urban location near the threshold of the piedmont and coastal plain zones of central North Carolina. The period for evaluation is June 2003 through May 2004. The weather variables that were closely examined include air temperature, dewpoint temperature, relative humidity, wind speed, and wind direction. In addition, radiation data was collected and analyzed including solar radiation, photosynthetically active radiation (PAR), net irradiance, diffuse radiation and direct radiation. Aerosol optical depths (AOD), which are the measurement of light attenuation at specified wavelengths, were also collected and evaluated in both the ultraviolet and visible light spectrums. This was done in order to determine any relationships between black carbon concentrations and AODs at certain wavelengths. After examining the year?s worth of data a site characterization involving the black carbon concentrations and meteorological variables for the Raleigh, NC location was devised.

Atmospheric rivers emanating from the tropics are responsible for the majority of the meridional transport of water vapor in the Northern Hemisphere, and have also been linked to episodes of heavy orographic precipitation along the mountains of the U.S West Coast. As moist air flow impinges on mountain ranges, orographic lifting converts water vapor to precipitation and can greatly reduce the moisture content of the airmass. The nearly along-coast parallel orientation of the Coastal and Sierra Nevada Ranges in Northern California, and the proximity of the Petaluma Gap to the south along the coast yield a geography, where moisture may enter the Sacramento Valley from multiple locations, complicating the quantification of airmass transformation over the region. Limitations of surface and satellite observing networks further complicate these calculations. In this study, the Weather Research and Forecasting Model (WRF) Version 2.2 is used to investigate the moisture flux and three-dimensional airmass transformation over northern California associated with the 29-31 December 2005 atmospheric river. Moisture flux analysis of the storm reveals that moisture enters the Sacramento Valley by both flowing over and around the Coastal Range. A large portion of the flow-over moisture is converted to precipitation along the windward slopes. Flow-around moisture enters through the Petaluma Gap, and then a significant portion is deflected northward by the strong barrier jet associated with the Sierra Nevada range. Moisture convergence and orographic lifting enhance precipitation along the slopes of the Sierra Nevada and Siskiyou Ranges. A drying ratio, or moisture reduction, of nearly 55% is found for the entire mountain complex, with 30% and 25% for the Coastal and Sierra Nevada Ranges, respectively. In a model sensitivity test where the Coastal Range is removed, the amount of moisture reaching the Sierras is only slightly increased compared to when the Coastal Range is present. When all terrain is removed, there is little reduction of moisture flux by the ocean/coast boundary, and the atmospheric river is able to penetrate deep into the western U.S.

Isotopic analyses of bone phosphate oxygen from a modern alligator, ostrich, and elephant have provided a means for examining diagenesis and thermoregulatory strategy within the dinosaur Acrocanthosaurus atokensis. The Acrocanthosaurus specimen is assumed to retain an original isotopic signature, based on a lack of linear correlation between δ18Ophosphate and structural δ18Ocarbonate, equal standard deviations between δ18Ophosphate values for spongy and compact bone, and a significant difference between δ18Ophosphate and cement δ18Ocarbonate. Interbone and intrabone temperature variation patterns suggest that Acrocanthosaurus followed a homeothermic pattern of heat distribution (i.e. maintenance of a 4°C temperature range). Comparison with the modern animals yields a closer resemblance to the ostrich and elephant versus the alligator, thereby suggesting Acrocanthosaurus was endothermic. The Acrocanthosaurus sacral spines and palatal bones show evidence of use as heat shedding structures and the braincase yields a significantly higher calculated temperature than the body.

<p> Aerosols affect the radiation budget of the earth-atmosphere system by directly reflecting or absorbing solar radiation and also indirectly, by altering the cloud albedo through changes in the cloud condensation nuclei concentration (CCN). Increases in CCN concentrations result in an increase in the cloud droplet number concentration (N). Assuming the cloud liquid water content (LWC) stays the same, this will result in smaller cloud droplet sizes. Thus, this will increase cloud reflectance and cloud lifetime as cloud cover also increases. An accurate quantification of the aerosol forcing effect is still not possible due to the complexity involved in understanding aerosol processes and their effects on climate. There has also been a lack of a coordinated effort toward linking surface and in situ observations, as well climate model results and satellite data. Due to the spatial and temporal heterogeneity in aerosol forcing, regional effects are important. In this dissertation, the direct and indirect radiative forcing effects of aerosols - primarily sulfates and to lesser extent soot aerosols at a site located in the southeastern U.S. are investigated by means of surface observations, modeling results and satellite data.During the summers of 1993-96, field experiments were conducted at Mt. Mitchell, North Carolina, at a site representative of the southeastern U.S. to determine the effect of pollutants on the cloud microphysical and optical properties. Analyses of the results from empirical relationships are used to obtain an estimate of the contribution of sulfates to indirect radiative forcing. Concurrent measurements of size resolved chemical concentrations, light scattering and absorption coefficients, aerosol size distribution and optical depth measurements were obtained during the winter of 1997 for cloud-free skies. Data from these measurements are used to investigate the chemical-physical-optical interaction between aerosols and to determine the direct forcing effect of aerosols by means of a column forcing model. Cloud water sulfate concentration is used as a measure of anthropogenic pollution. Back-trajectory analysis is used to identify the source of the air masses classified as polluted continental, continental and marine. The effect of anthropogenic pollution on cloud microphysical properties such as LWC, N, effective radii (Reff), CCN activation spectrum, cloud optical depth and reflectivity are investigated. The relationship between Reff and sulfate for different air masses, as well as the N-sulfate mass relationship, suggests that the counteracting effect of sulfates on greenhouse warming for the southeastern U.S. would be of a magnitude greater than -4.0 W m-2 obtained by previous modeling studies. Acidity variations between cloud droplets of different sizes indicated that on an average, smaller drops are enriched in sulfates, nitrates and ammonium, whereas, larger droplets have higher concentrations of sodium, calcium and magnesium. As part of a closure experiment cloud albedo calculated from in situ measurements was compared to that retrieved from the Advanced Very High Resolution Radiometer data for four years (1993-96). The nonlinear relationships between the cloud microphysical/optical properties and the sulfate content imply the existence of an optimum level for the sulfate concentration that would affect cloud albedo. In terms of the direct forcing effect, wintertime forcing obtained for an internal mixture of sulfate and soot aerosols is much lower than that obtained during summer, due to reduced sulfate concentrations in winter. A quantitative measure of the direct forcing indicates higher magnitudes both for summer and winter than is obtained from previous modeling results. Analyses of the direct and indirect radiative forcing effect of sulfates for the southeastern U.S. indicate that the negative forcing effect is of greater magnitude than is predicted by modeling results. Thus, reduction in sulfate emissions would have a significant impact on climate for the southeastern U.S. <P>

<p>The purpose of the research has been to provide a better understanding of the climatology, variability, mechanisms, physical processes, and predictability of the Intertropical Convergence Zone (ITCZ), one of the most prominent and important features of the tropical atmosphere. The effort is focused on six different tasks based on statistical and numerical methods. Analysis of the mean and meridional profile of the global ITCZ suggests that each tropical ocean domain has different structure and latitude preference of convection due to different interactions between the oceans and the atmosphere. Moreover, the power spectrum density analysis shows that regions of the dominant interannual variation of deep convection occur over Indonesia and the central Pacific. With respect to the annual cycle, large variations in convection are mainly over the monsoon and continental regions. At the semiannual time scale, convection is greatest over the Indian subcontinent and Australia. The relationships between sea surface temperature, large-scale atmospheric circulation, and convective activity in tropical oceans are examined in the second study by the regression analysis. The results show that the relationship between sea surface temperature and convection is strongly influenced by the large-scale circulation, particularly in the Indian and western Pacific oceans. However, the relationship between large-scale circulation and convection is less dependent on SST in all the ocean domains. In the third study, the relationship and long-term predictability between sea surface temperature anomalies over the Pacific Ocean during El Nino/La Nina events and convective anomalies over Indonesia are examined using the Empirical Orthogonal Function (EOF) and Canonical Correlation Analysis (CCA) techniques. The results show that the models are potentially useful in predicting convective anomalies over Indonesia during boreal fall and winter months up to six months ahead. On the other hand, the models have lower skills in spring and summer months caused by the reduction of the east-west pressure gradients of the Southern Oscillation and the so-called spring barrier. The numerical simulations presented in the last three studies are performed to study the dynamics and the physics of the ITCZ system. The behavior of the northeast monsoon over the Indian Ocean and Indonesia during a normal and during an El Nino/Southern Oscillation (ENSO) year is compared using the Naval Research Laboratory/North Carolina State University (NRL/NCSU) model and the Fifth Generation of the Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model (PSU-NCAR MM5). During the active monsoon in 1997, both models generally simulate the mean circulations up to 24 hours, but show rapid decline in the forecasts beyond that when the winds become stronger. In contrast, when the synoptic-scale dynamic forcing was strong during the 1998 ENSO event, the simulated mean flows are in good agreement with the analyses up to 48 hours. It is also found that the rates and distributions of oceanic and land mass rainfall are more realistically simulated by the NRL/NCSU model than by the PSU-NCAR MM5 for these two cases. The model errors can be attributed among others to the inaccuracies in the PBL parameterization and uncertainties in the initial conditions. In the fifth study, the transport of air parcels during the 1997 forest fires in Kalimantan, Indonesia is investigated using simulated wind fields from the PSU-NCAR MM5. The interactions between the synoptic conditions and the regional winds are found to be very important on the long-range mean transport. Drought conditions and the persistence of strong easterly winds caused air masses from east and south Kalimantan to travel a distance of 1500 km in only four days. Finally, in the sixth study the PBL structure simulated from the PSU-NCAR MM5 and its role in the transport of air masses during the Indian Ocean Experiment 99 (INDOEX 99) are examined. Results indicate that during undisturbed conditions, the PBL over the Indian Ocean reaches its maximum height in the night hours and minimum height in the early morning hours. Near the coast, localized low-level circulations are simulated in which the air parcels are trapped. An elevated land plume is also simulated over the ocean.<P>

<p>The Intergovernmental Panel on Climate Change (IPCC) has reported that in the southeastern US and eastern China, the general greenhouse warming due to anthropogenic gaseous emissions is dominated by the cooling effect of anthropogenic aerosols. To verify this model prediction in eastern China and southeastern US, we analyzed regional patterns of climate changes at 72 stations in eastern China during 1951-94 (44 years), and at 52 stations in the southeastern US during 1949-94 (46 years) to detect the fingerprint of aerosol radiative forcing. It was found that the mean rates of change of annual mean daily, maximum, minimum temperatures and diurnal temperature range (DTR) in eastern China were 0.8, -0.2, 1.8, and -2.0 C/100 years respectively, while the mean rates of change of annual mean daily, maximum, minimum temperatures and DTR in the southeastern US were -0.2, -0.6, 0.2, and -0.8 C/100 years, respectively. This indicates that the high rate of increase in annual mean minimum temperature in eastern China results in a slightly warming trend of daily temperature, while the high rate of decrease in annual mean maximum temperature and low rate of increase in annual mean minimum temperature lead to the cooling trend of daily temperature in the southeastern US. We found that the warming from the longwave forcing due to both greenhouse gases and aerosols was completely counteracted by the shortwave aerosol forcing in the southeastern US in the past 46 years. A slightly overall warming trend in eastern China is evident; winters have become milder. This finding is explained by hypothesizing that increasing energy usage during the past 44 years has resulted in more coal and biomass burning, thus increasing the emission of absorbing soot and organic aerosols in eastern China. Such emissions, in addition to well-known Asia dust and greenhouse gases, may be responsible for the winter warming trend in eastern China that we have reported here.The sensitivity of aerosol radiative properties to aerosol composition, size distribution, relative humidity (RH) is examined for the following aerosol systems: inorganic and organic ions (Cl-, Br-, NO3-, SO42-, Na+, NH4+, K+, Ca2+, Mg2+, HCOO-, CH3COO-, CH3CH2COO-, CH3COCOO-, OOCCOO2-, MSA-1); water-insoluble inorganic and organic compounds (elemental carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method was used to calculate the real part of the refractive index. It was found that the asymmetry factor increased by ~48% with the real part varying from 1.40 to 1.65, and the single scattering albedo decreased by 24% with the imaginary part varying from -0.005 to -0.1. The asymmetry factor increased by 5.4 times with the geometric standard deviation varying from 1.2 to 3.0. The radiation transmission is very sensitive to the change in size distribution; other factors are not as significant.To determine the aerosol direct radiative forcing (ADRF), the aerosol optical depth (AOD) values at the three operational wavelengths (415, 500 and 673 nm) were determined at a regionally representative site, namely, Mt. Gibbs (35.780 N, 82.290 W, elevation 2006 m) in Mt. Mitchell State Park, NC, and a site located in an adjacent valley (Black Mountain, 35.660 N, 82.380 W, elevation 951 m) in the southeastern US. The two sites are separated horizontally by 10 km and vertically by 1 km. It was found that the representative total AOD values at 500 nm at the valley site for highly polluted (HP), marine (M) and continental (C) air masses were 0.68+/-0.33, 0.29+/-0.19 and 0.10+/-0.04, respectively. A search-graph method was used to retrieve the columnar size distribution (number concentration N, effective radius reff and geometric standard deviation sg) from the optical depth observations at three operational wavelengths. The ground albedo, single scattering albedo and imaginary part of the refractive index were calculated using a mathematically unique procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, AOD, and diffuse-direct irradiance ratio. It was found that N, reff and sg were in the ranges of 10 to 1.7x104 cm-3, 0.09 to 0.68 mm and 1.12 to 2.95, respectively. The asymmetry factor and single scattering albedo were in the ranges of 0.63 to 0.75 and 0.74 to 0.97 respectively. The ground albedo for the forested terrain and imaginary part of refractive index were found to be in the ranges of 0.06 to 0.29 and 0.005 to 0.051 respectively. On the basis of these aerosol radiative properties obtained at the research sites and computations using the Column Radiation Model (CRM) of National Center of Atmospheric Research (NCAR) Community Climate Model (CCM3), it was found that the average cloud-free 24-hour ADRF values were -13+/-8, -8+/3, -33+/-16 W m-2 for marine, continental, and polluted air masses, respectively. On the assumption that the fractional coverage of clouds is 0.61, it was estimated that the annual mean ADRF was 7+/-2 W m-2 in the southeastern US.The review with respect to the current knowledge of organic acids shows that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol/m3 and from 0.03 to 12.4 nmol/m3 respectively, and that between 34% to 77% of formate and between 21% to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile organic acids were present in the gas phase, their concentrations in the aerosol particles were sufficient to make them a good candidate for cloud condensation nuclei (CCN). It is hypothesized that organic acids are at least one of the primary sources of CCN in the atmosphere due to their ubiquitous presence in the troposphere, especially over the continental forested areas. The results of our measurements at Palmer Station, Antarctica show that the daily average CCN concentrations at 0.3% and 1% supersaturations ranged from 0.3 to 160 cm-3 and from 4 to 168 cm-3, respectively, during the period from 17 January to 26 February, 1994. New evidence for substantial and definitive CCN enhancement near and within cloud has been observed at Mt. Mitchell, North Carolina. The results show that the average monthly CCN concentrations were 460+/-217, 386+/-286, 429+/-228 and 238+/-134 cm-3 for in-cloud, overcast, clear and rainy conditions, respectively. The typical CCN spectra show that there were a lot of small CCN produced and the ion concentrations (especially H+ and SO42-) were very high during the CCN enhancement period. The significantly positive correlation between black carbon (BC) and CCN at 1% supersaturation indicates that a percentage of the BC measured at the site may be in the form of an internal mixture and participated in the formation of CCN. <P>

<p>ABSTRACTPOULIOT, GEORGE. A Variable Resolution Nonhydrostatic Global Atmospheric Semi-implicit Semi-Lagrangian Model. (Under the direction of Dr. Fredrick H.M. Semazzi.)The objective of this project is to develop a variable-resolution finite difference adiabatic global nonhydrostatic semi-implicit semi-Lagrangian (SISL) model based on the fully compressible nonhydrostatic atmospheric equations. To achieve this goal, a three-dimensional variable resolution dynamical core was developed and tested.The main characteristics of the dynamical core can be summarized as follows: Spherical coordinates were used in a global domain. A hydrostatic/nonhydrostatic switch was incorporated into the dynamical equations to use the fully compressible atmospheric equations. A generalized horizontal variable resolution grid was developed and incorporated into the model. For a variable resolution grid, in contrast to a uniform resolution grid, the order of accuracy of finite difference approximations is formally lost but remains close to the order of accuracy associated with the uniform resolution grid provided the grid stretching is not too significant. The SISL numerical scheme was implemented for the fully compressible set of equations. In addition, the generalized minimum residual (GMRES) method with restart and preconditioner was used to solve the three-dimensional elliptic equation derived from the discretized system of equations. The three-dimensional momentum equation was integrated in vector-form to incorporate the metric terms in the calculations of the trajectories. Using global re-analysis data for a specific test case, the model was compared to similar SISL models previously developed. Reasonable agreement between the model and the other independently developed models was obtained. The Held-Suarez test for dynamical cores was used for a long integration and the model was successfully integrated for up to 1200 days. Idealized topography was used to test the variable resolution component of the model. Nonhydrostatic effects were simulated at grid spacings of 400 meters with idealized topography and uniform flow. Using a high-resolution topographic data set and the variable resolution grid, sets of experiments with increasing resolution were performed over specific regions of interest. Using realistic initial conditions derived from re-analysis fields, nonhydrostatic effects were significant for grid spacings on the order of 0.1 degrees with orographic forcing. If the model code was adapted for use in a message passing interface (MPI) on a parallel supercomputer today, it was estimated that a global grid spacing of 0.1 degrees would be achievable for a global model. In this case, nonhydrostatic effects would be significant for most areas.A variable resolution grid in a global model provides a unified and flexible approach to many climate and numerical weather prediction problems. The ability to configure the model from very fine to very coarse resolutions allows for the simulation of atmospheric phenomena at different scales using the same code. We have developed a dynamical core illustrating the feasibility of using a variable resolution in a global model.<P>