No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Stellar abundances are essential parameters for many branches of astronomy. They are also particularly important as tests for theories of nucleosynthesis. Despite the encouraging results from band photometry, detailed spectroscopic analyses are still important in furthering knowledge of physical processes occurring in a variety of stellar objects. This thesis presents the first of a series of absolute abundances for the late-type giant Arcturus. The broader aim of the investigation is to make Arcturus a reliable standard star, and also it is hoped that equilibrium assumptions in its atmosphere can be scrutinised. An essential prerequisite to a model atmosphere is the continuum flux curve. Certain discrepancies near the flux maximum prompted the construction of a spectrum scanner which was used to obtain fluxes of Arcturus at the Wise Observatory, Israel. All known flux results have been collated for Arcturus, and the continuum flux curve is presented for the region 3800 andAring; to 13 microns. Ways of measuring the effective temperature are discussed. The only adequate method for Arcturus and other cool stars involves comparing the relative energy distribution with model predictions. As all present models fail to account for the flux below 5000 andAring; this method is not as accurate as it could be. A value of 4450 ± 50°K is adopted for Arcturus; most of this error is due to the unrealistic nature of the models. Using this temperature a grid of line-blanketed models with different gravities has been constructed. The suggested gravity-indicator requires a precise value for the microturbulence, and for this preliminary analysis a model with log g = 1.7 was selected. This value, reported by several investigators, is later shown to be fairly realistic. Uncertain oscillator strengths continue to plague abundance work in astronomy, though the Oxford furnace is now producing precision values for several elements. Using this furnace a series of neutral titanium lines of direct astrophysical interest have been measured, and they are accurate to at least ±0.03 dex(7%) on a relative scale. Considerable effort is still needed in establishing accurate absolute scales however; these results have been made absolute by referring to theoretical and observational lifetimes. The internal consistency of the Ti I values has been verified by studying the solar abundance of titanium. Rf restricting the analysis to good quality weak lines, uncertainties in damping and microturbulence have been avoided. A log abundance of 4.81 ± 0.08 is reported (on the log H = 12.00 scale). For the Arcturus analysis, a few iron lines have also been included. In this star the abundances are very sensitive to the value assumed for the microturbulence. The empirical nature of this parameter is emphasised. A value of 2.1 ± 0.2 km sec^-1 was found by demanding an unique abundance for all lines. Theories accounting for the origin of iron-peak elements are discussed. Explosive Silicon burning cannot account for all the observed isotopes, and the equilibrium process has been re-introduced to explain some anomalies. These theories are examined in relation to supernova models and Galactic evolution, and also with regard to the broader purpose and prospects for measurements of stellar abundances.

Warming of both the high latitudes and tropical sea surface temperatures are present in modern observations and projected under future climate change scenarios. These conditions were also present in the Warm Pliocene (3.3 - 3.0 million years ago), a paleoclimatic interval that bares resemblance to future global warming. This dissertation investigates the impact of both tropical and high latitude warming on regional atmospheric circulation using GISS global climate model simulations of the Pliocene and sensitivity tests. Chapter 1 discusses the initial approach used to investigate how a warmer climate impacts regional atmospheric circulation. A general circulation model (GCM) was utilized to assess the contribution from both high latitude and tropical warming to regional Pliocene climatic patterns. It was found that both a warming of the high latitudes and Indo-Pacific tropical region are needed to reproduce the regional Pliocene climates indicated by terrestrial paleo-proxy data. These results suggest that the tropical atmospheric circulation of the Indo-Pacific region during the warm Pliocene may have been different from modern mean conditions. These findings are corroborated by Pliocene paleo-data, a luxury not afforded by future climate projections, and provide insight into possible regional atmospheric circulation processes in a future warmer climate. Chapter 2 (Shukla et al., 2011) investigates how exactly the Indo-Pacific circulation and global teleconnections differed from modern day conditions. GCM generated teleconnections from the Indo-Pacific region were examined from origin to their impact on the extra-tropics under warm Pliocene conditions. The exact forcing source was not assumed a-priori, and it was found that while warmer SSTs in the eastern tropical Pacific generated weak El Niño-like teleconnections to North America, their effects over the Indian Ocean region were attenuated, primarily by the warmer SSTs there. Teleconnections to the extra-tropics were largely blocked from the Indian Ocean region, and most of the energy generated by the SST patterns went into maintaining an anomalous atmospheric overturning circulation. This altered background circulation of the Indian Ocean region can impact the South Asian Summer Monsoon (SASM) system. In these simulations, the dynamic monsoon intensity experienced the greatest decrease with tropical warming alone. Lesser SASM weakening occurred when both tropical and high latitude warming were imposed. Given the potential Indo-Pacific SSTs changes under Pliocene and warm climate conditions, Chapters 3 and 4 focus on the implications these changes have for the South Asian Summer Monsoon circulation. Chapter 3 examines the GISS suite of GCMs' ability to reproduce the major features of the South Asian Summer Monsoon (SASM) system. The GISS Model E (atmosphere only), Middle Atmospheres Model 3 (atmosphere only) and the ocean-atmosphere coupled Model E were run using forcings from 1960-2008. Major indices and features of the SASM were evaluated and compared to NCEP/NCAR and ECMWF reanalysis data. It was found that the atmosphere-only Model E better simulated, both in magnitude and variability, the circulatory (wind, vorticity, etc.) components of the SASM, whereas the coupled ModelE better simulated the magnitude of rainfall over the Indian sub-continent. Chapter 3 highlighted the SASM features in the models that need improvement, specifically in the overproduction of rainfall and the underestimation of windspeeds. Given the relatively accurately modelE simulated SASM intensity variability, and acknowledging its underestimation of wind strength, continuing modelE studies of the SASM will focus on large-scale circulation processes, rather than the rainfall distribution and variability. Chapter 4 compares SASM changes under both Pliocene conditions and future climate projections, the latter dictated by the Representative Concentration Pathways (RCPs). A tropical SST forcing, in the form of warmer western tropical Indian Ocean and eastern tropical Pacific Ocean SSTs, was additionally tested in isolation from globally warmer conditions. It was found that the SASM weakens under globally warmer conditions, but the greatest weakening occurred under tropical forcing alone. This suggests the importance of the relative regional temperature gradients of the Indian Ocean region. Although both simulations served to weaken the SASM system, the regional climatic patterns differed between Pliocene and future simulations and warrant further investigation. Future studies must focus on obtaining more data from the Indian Ocean region for the Pliocene period in order to corroborate modeled climate processes in that region. In addition, more assessments must be done to understand difference between climate processes in future projections and past warm climate intervals as this will aid in model development and our understanding of the climate's response and sensitivity.

Aerosol production from surface waters results in the transfer of aquatic materials (including nutrients and bacteria) to air. These materials can then be transported by onshore winds to land, representing a biogeochemical connection between aquatic and terrestrial systems not normally considered. In urban waterfront environments, this transfer could result in emissions of pathogenic bacteria from contaminated waters. Despite the potential importance of this link, sources, near-shore deposition, identity and viability of microbial aerosols are largely uncharacterized. This dissertation focuses on the environmental and biological mechanisms that define this water-air connection, as a means to build our understanding of the biogeochemical, biogeographical, and public health implications of the transfer of surface water materials to the near-shore environment in both urban and non-urban environments. The effects of tidal height, wind speed and fog on coastal aerosols and microbial content were first quantified on a non-urban coast of Maine, USA. Culture-based, culture-independent, and molecular methods were used to simultaneously sample microbial aerosols while monitoring meteorological parameters. Aerosols at this site displayed clear marine influence and high concentrations of ecologically-relevant nutrients. Coarse aerosol concentrations significantly increased with tidal height, onshore wind speed, and fog presence. Tidal height and fog presence did not significantly influence total microbial aerosol concentrations, but did have a significant effect on culturable microbial aerosol fallout. Molecular analyses of the microbes settling out of near-shore aerosols provided further evidence of local ocean to terrestrial transport of microbes. Aerosol and surface ocean bacterial communities shared species and in general were dominated by organisms previously sampled in marine environments. Fog presence strengthened the microbial connection between water and land through air by increasing microbial aerosol settling rates and enhancing viability of aerosolized marine microbes. Using methods developed for the non-urban site, the role of local environment and winds in mediating water-air connections was further investigated in the urban environment. The local environment, including water surfaces, was an important source of microbial aerosols at urban sites. Large portions of the urban waterfront microbial aerosol communities were aquatic and, at a highly polluted Superfund waterfront, were closely related to bacteria previously described in environments contaminated with hydrocarbons, heavy metals, sewage and other industrial waste. Culturable urban aerosols and surface waters contained bacterial genera known to include human pathogens and asthma agents. High onshore winds strengthened this water-air connection by playing both a transport and production role. The microbial connection between water and air quality outlined by this dissertation highlights the need for information on the mechanisms that deliver surface water materials to terrestrial systems on a much larger scale. Moving from point measurements to landscape-level analyses will allow for the quantitative assessment of implications for this microbial water-air-land transfer in both urban and non-urban arenas.

Tropical cyclones (TC) in the western North Pacific (WNP) pose a serious threat to the coastal regions of Eastern Asia when they make landfall. The limited amount of observational data and the high computational cost of running TC-permitting dynamical models indicate a need for statistical models that can simulate large ensembles of TCs in order to cover the full range of possible activity that results from a given climate change. I construct and apply a statistical track model from the 1945-2007 observed "best tracks" in the IBTrACS database for the WNP. The lifecycle components--genesis, track propagation, and death--of each simulated track is determined stochastically based on the statistics of historical occurrences. The length scale that dictates what historical data to consider as "local" for each lifecycle component is calculated objectively through optimization. Overall, I demonstrate how a statistical model can be used as a tool to translate climate-induced changes in TC activity into implications for risk. In contrast to other studies, I show that the El Niño/Southern Oscillation (ENSO) has an effect on track propagation separate from the genesis effect. The ENSO effect on genesis results in higher landfall rates during La Niña years due to the shift in genesis location to the northeast. The effect on tracks is more geographically and seasonally varied due to local changes in the mid-level winds. I use local regression techniques to capture the relationship between ENSO, cyclogenesis, and track propagation. Stationary climate simulations are run for extreme ENSO states in order to better understand changes in TC activity and their implication for regional landfall. Additionally, Several diagnostics are performed on model realizations of the historical period, confirming the model's ability to capture the geographical distribution and interannual variability of observed TCs. Lastly, as a step to connect synthetic TC track simulations to economic damage risk assessment, I use a Damage Index and total damage data for U.S. landfalling hurricanes and fit generalized Pareto distributions (GPD) to them. The Damage Index uniquely separates out the effects of the physical damage capacity of a TC and the local economic vulnerability of a coastal region. GPD fits are also performed using covariates in the scale parameter, where bathymetric slope and landfall intensity are found to be useful covariates for the Damage Index. Using the Damage Index with covariates model, two examples are shown of assessing damage risk for different climates. The first takes landfall data input from a statistical-deterministic TC model downscaled from GFDL and ECHAM model current and future climates. The second takes landfall data from a fully statistical track model with different values of relative sea surface temperature given as a statistical predictor.