A comprehensive theory explaining the relationship between periodic variations in the Earths orbital parameters and the response of the climate system remains elusive. One of the key challenges is that of the Mid-Pleistocene Transition (MPT), during which the dominant mode of glacial/interglacial climatic variability shifted without any corresponding change in the mode of orbital forcing. Subtropical climate on orbital time-scales is sensitive to variability in both the low-latitude ocean/atmosphere circulation regime and the global carbon-cycle (through its effect on atmospheric greenhouse gas levels), both of which may have played a role in the shift in mode of global climate response to orbital forcing during the MPT. This thesis presents a series of multi-proxy (foraminiferal stable isotope and trace-metal) paleoceanographic reconstructions from the subtropical southwest Pacific, as seen in marine sediment core MD06-3018, from 2470m water depth and 23ºS in the New Caledonia Trough, southern Coral Sea. The core age-model, based upon magnetic stratigraphy and orbital tuning, yields a mean sedimentation rate at the site of 20mm/ka and a core-bottom age of 1600ka. The MD06-3018 reconstruction of New Caledonia Trough deep water chemistry, based on benthic 13C measurements, shows that the spatial chemistry gradient within the Southern Ocean between deep waters entering the Tasman Sea and the open Pacific was greater during glacial (relative to interglacial) stages over at least the past 1100ka. This gradient was, however, generally reduced on the >100kyr time-scale across the MPT, consistent with it being a period of reduced deep water ventilation in both hemispheres. The MD06-3018 Mg/Ca-derived reconstruction of subtropical southwest Pacific Sea Surface Temperature (SST) shows glacial/interglacial variability of 2-3ºC but no significant trends on the >100kyr time-scale over the duration of the record. An estimate of the uncertainty associated with the SST reconstruction demonstrates that no significant changes in reconstructed southern Coral Sea mean-annual SST can be identified between interglacial stages across the MPT. It is, therefore, unlikely that regional climatic change constituted the main cause for the observed middle Pleistocene expansion of coral reef systems. The >100kyr time-scale stability of southern Coral Sea SST means that the position of the southern boundary of the Pacific warm pool has also been stable over at least the past 1500ka. Comparison with other low-latitude Pacific reconstructions shows that the early Pleistocene warm pool was consequently more hemispherically asymmetric than its present configuration, with the latter being established by ~1000ka and implying significant changes in meridional atmospheric heat and moisture fluxes prior to the MPT. On orbital time-scales, the SST reconstruction shows a clear shift from dominant 40kyr to 100kyr modes of variability over the MPT, although significant 40kyr structure is also retained into the middle/late Pleistocene. In contrast, reconstructed hydrological cycle variability (based on coupled 18O-Mg/Ca measurements) shows only limited coherence with the obliquity cycle and a stronger relationship with the precession cycle. The decoupling of the reconstructed subtropical SST and hydrological cycle responses places constraints on the extent of orbitally paced fluctuations in the low-latitude ocean/atmosphere system. Instead, comparison of the MD06-3018 SST reconstruction with others from across the lowlatitude Pacific supports a dominant role for greenhouse gas forcing in low-latitude western Pacific glacial/interglacial SST variability across the Pleistocene. The subtropical multi-proxy climate reconstructions presented here show that the timing and sense of long-term (>100kyr time-scale) changes in the low-latitude ocean/atmosphere circulation regime are consistent with that system having been important in the expansion of northern hemisphere ice-volume during the early part of the MPT. However, the subtropical reconstructions also suggest that neither the low-latitude ocean/atmosphere circulation system nor the global carbon-cycle underwent a fundamental change in mode of response to orbital forcing during the transition. Instead, the origin of the 100kyr glacial/interglacial mode was most likely related to thresholds in the dynamics of the expanding northern hemisphere icesheets, leading in turn to the existence of significant inter-hemispheric asymmetry in the orbital time-scale climate response over the middle/late Pleistocene. Summary for Non-Specialists. Over the past five million years of its history, the Earths climate has undergone a series of regular, or nearly regular, fluctuations between warmer and colder states. These fluctuations take tens to hundreds of thousands of years to occur and are known as the ‘glacial/interglacial cycles’ on account of the associated changes in ice-sheet extent in the high-latitudes. The origin of these cycles is widely held to be the regular variations in form of the Earths orbit around the sun. In spite of decades of research, however, no complete ‘orbital theory of climate’ exists, mainly because the patterns of past climate variability, as reconstructed using ‘proxies’ for variables such as surface temperature, is much more complex than that of the orbital variations themselves. It follows that processes within the Earth system, especially those associated with large ice-sheets, the carbon-cycle and the ocean circulation system, act to substantially modify the climate response to the orbital variations. Over the past ten years, new observations from both ice-cores and low-latitude marine sediment cores have suggested that the dominant system(s) involved in setting the Earths response to the orbital variations may potentially be the carboncycle and/or the low-latitude ocean/atmosphere circulation regime rather than highlatitude ice-sheet dynamics, as was generally supposed previously. If this new view is correct, it has profound implications for the general sensitivity of the climate to the carbon-cycle on a range of time-scales - making its evaluation a scientific objective of considerable current importance. This thesis presents a series of reconstructions of aspects of climate and carbon-cycle variability for the subtropical southwest Pacific, as based on proxy measurements in a marine sediment core than spans the past 1,600,000 years at around 5000 year resolution. The key focus is on an interval called the ‘Mid- Pleistocene Transition’, during which time the mode of glacial/interglacial variability changed, indicating a fundamental change in one or more aspects of the response to the orbital forcing. The study site is well placed to investigate variability in both the carbon-cycle and low-latitude ocean circulation over the climatic transition as it lies between the Southern Ocean, a key source of carbon-cycle variability and the equatorial Pacific, where the modern El-Niño system arises. By characterizing variability in these systems, the potential role played by both systems in causing the change in mode of glacial/interglacial variability can be evaluated. The key findings of the thesis are that; firstly, changes in the long-term state of the low-latitude ocean circulation system may well have been important for the expansion of northern hemisphere ice-sheets during the early part of the Mid- Pleistocene Transition. Secondly, it provides further support for a close connection between variability in the carbon-cycle and low-latitude climate on orbital timescales but suggests that there is no clear evidence for either system undergoing a fundamental change in sensitivity to the orbital forcing during the transition.

Four regional Scots pine ring-width chronologies at the northern forest-limit, and in the northern, middle and southern boreal forest belts in Finland cover the last fourteen centuries. Tree-ring statistics and response functions were examined, and tree-ring width variation was also compared to North Atlantic Oscillation (NAO) and volcanic forcing. The tree-ring statistics show evidence of an ecogeographical gradient along a north-south transect. The three northernmost regional chronologies share a positive response to mid-summer temperature, and all four chronologies show positive and significant correlation to early-summer precipitation. Moreover, a positive and significant relationship to winter NAO was detected in three out of four regional chronologies. NAO also drives the common (inter-regional) growth variability. Years of known cool summers caused by volcanic forcing exhibit exceptionally narrow tree rings in the three northernmost regional chronologies.

The global analysis fields of the Met Office stratospheric assimilated data set have been investigated. Systematic biases for select years were identified through val- idation with independent satellite observations. Particular attention was given to analyses from January 2005 to October 2009 produced from a 50 level (L50) configuration of the UM with model lid at ∼0.1 hPa, and the impact on analyses fields from November 2009 to September 2010 when the middle atmospheric configuration of the UM was extended to ∼0.01 hPa using 70 levels (L70). Validation results from both the L50 and L70 analyses show that largest tem- perature biases occur at polar latitudes approaching the model lid in the meso- sphere, exhibiting a clear seasonal cycle. Here cold biases in the winter season of the L50 analyses and warm biases in the summer season of the L70 analyses would strongly suggest that the mean meridional circulation in the mesosphere is underestimated, and that small scale gravity wave forcing supplied by the op- erational Ultra Simple Spectral Parameterisation (USSP) scheme is insufficient. Based on the above validation results numerous experiments were conducted to investigate the temperature response in the mesosphere to increased gravity wave forcing. Such experiments concentrated on tuning the energy scale factor (β) in the USSP scheme and the application of a momentum conserving ”opaque” lid. Furthermore, the impact of developing the USSP scheme to include direct heating from gravity wave induced turbulent dissipation was also investigated. Maximum temperature responses in the summer polar upper mesosphere of ∼22 K were found when increasing the standard value of β=0.1 to β=0.14 combined with the application of an opaque lid. Magnitudes of direct heating rates due to gravity wave turbulent dissipation diagnosed via the USSP scheme were found to be consistent with previous estimates. However applying such heating would most likely have a negative impact on the L70 analyses, which already display warm biases in the upper mesosphere, strongly suggesting that additional phys- ical processes such as eddy diffusion must also be accounted for when applying direct heating from gravity wave breaking.

A 12-month study (January to December 2015) focused on the effects of tidal forcing on nutrient fluxes in the tidal, freshwater segment of the James River Estuary (JRE). Discrete sampling of nutrient chemistry and continuous monitoring of tidal discharge were used to determine the volume and timing of the tides, and differences in nutrient concentrations between incoming and outgoing tides. The goal of this study was to improve understanding of tidal influence on nutrient fluxes and their role in nutrient transport to the lower estuary. Results suggested that differences in nutrient concentrations between incoming and outgoing tides were small throughout the year. This finding suggests that nutrient fluxes at the study site, near the tidal fresh-oligohaline boundary of the James, are largely determined by tidal volume owing to weak concentrations gradients. Changes in water quality during seaward and landward tidal excursions into deeper versus shallower segments were analyzed to infer biogeochemical processes. Differences in oxygen production and nitrate utilization suggest greater autotrophy during landward excursions, consistent with more favorable light conditions. This work was conducted as a collaborative effort between Virginia Commonwealth University, the USGS, Randolph-Macon College, and Washington and Lee University participating in the “Mountains to the Sea” project.

This thesis is comprised of two parts. The first part (Chapter 1) concerns a problem born from descriptive set theory, and is motivated by the desire to understand a particular topological game, in the presence of examples which exhibit interesting (arguably counterintuitive) behaviour. The work develops an understanding of the limits of this behaviour, and indicates where one might look for interesting examples. While set-theoretic techniques may appear in the analysis here, the focus is mostly topological. The second part (Chapter 2) is much more set-theoretic. The work there developed from an interest in characterising closed subsets of βω, and focuses on developing tools which are promising for generalising the current relative consistency proofs of a duality principle for closed subsets of βωω. Knowledge of forcing comparable to that contained in Kunen and Jech is assumed. The appendices contain results which are worthy of inclusion, and help provide additional perspective on the rest of the text. The results there are probably all already known, if not all recorded in the literature.

Approved for public release; distribution in unlimited. / Numerical ocean modeling usually composes various initial- and boundary-value problems. It integrates hydrodynamic and thermodynamic equations numerically with atmospheric forcing and boundary conditions (lateral and vertical) from initial states of temperature, salinity and velocity. Past observations, historical datasets and climatological datasets of the ocean have contributed greatly to the knowledge of the data fields of initial condition, atmospheric forcing and boundary conditions. Change in either initial or boundary condition leads to a variety of model solutions. It is necessary to specify realistic initial and boundary conditions to achieve better understanding and prediction of the ocean behavior. However, uncertainty often exists in both initial and boundary conditions. Up to now, most studies on ocean predictability have usually been for one particular type of model input uncertainty within the three types of uncertainty (initial conditions, open boundary conditions, atmospheric forcing function). This thesis investigates the response of ocean model to the three types of model input uncertainty simultaneously using Princeton Ocean Model (POM) implemented for the Japan/East Sea (JES). / Lieutenant Commander, Taiwan, R.O.C. Navy

Mineral dust aerosol plays an important role in determining the physical and chemical equilibrium of the atmosphere. The radiative balance of the Earth's atmosphere can be affected by mineral dust through both direct and indirect means. Mineral dust can directly scatter or absorb incoming visible solar radiation and outgoing terrestrial IR radiation. Dust particles can also serve as cloud condensation nuclei, thereby increasing albedo, or provide sites for heterogeneous reactions with trace gas species, which are indirect effects. Unfortunately, many of these processes are poorly understood due to incomplete knowledge of the physical and chemical characteristics of the particles including dust concentration and global distribution, as well as aerosol composition, mixing state, and size and shape distributions. Much of the information about mineral dust aerosol loading and spatial distribution is obtained from remote sensing measurements which often rely on measuring the scattering or absorption of light from these particles and are thus subject to errors arising from an incomplete understanding of the scattering processes. The light scattering properties of several key mineral components of atmospheric dust have been measured at three different wavelengths in the visible. In addition, measurements of the scattering were performed for several authentic mineral dust aerosols, including Saharan sand, diatomaceous earth, Iowa loess soil, and palagonite. These samples include particles that are highly irregular in shape. Using known optical constants along with measured size distributions, simulations of the light scattering process were performed using both Mie and T-Matrix theories. Particle shapes were approximated as a distribution of spheroids for the T-Matrix calculations. It was found that the theoretical model simulations differed markedly from experimental measurements of the light scattering, particularly near the mid-range and near backscattering angles. In many cases, in the near backward direction, theoretical models predicted scattering intensities for near spherical particles that were up to 3 times higher than the experimentally measured values. It was found that better agreement between simulations and experiments could be obtained for the visible scattering by using a much wider range of more eccentric particle shapes.

Deteriorating air quality is one of the major problems faced worldwide and in particular in Asia. The world's most polluted megacities are located in Asia highlighting the urgent need for efforts to improve the air quality. New Delhi (India), one of the world's most polluted cities, was the host of the Common Wealth Games during the period of 4-14 October 2010. This high profile event provided a good opportunity to accelerate efforts to improve air quality. Computational advances now allow air quality forecast models to fully couple the meteorology with chemical constituents within a unified modeling system that allows two-way interactions. The WRF-Chem model is used to simulate air quality in New Delhi. The thesis focuses on evaluating air quality and meteorology feedbacks. Four nested domains ranging from South Asia, Northern India, NCR Delhi and Delhi city at 45km, 15km, 5km and 1.67km resolution for a period of 20day (26thsep-15thoct, 2010) are used in the study. The predicted mean surface concentrations of various pollutants show similar spatial distributions with peak values in the middle of the domain reflecting the traffic and population patterns in the city. Along with these activities, construction dust and industrial emissions contribute to high levels of criteria pollutants. The study evaluates the WRF-Chem capabilities using a new emission inventory developed over Delhi at a fine resolution of 1.67km and evaluating the results with observational data from 11 monitoring sties placed at various Game venues. The contribution of emission sectors including transportation, power, industry, and domestic to pollutant concentrations at targeted regions are studied and the results show that transportation and domestic sector are the major contributors to the pollution levels in Delhi, followed by industry. Apart from these sectors, emissions outside of Delhi contribute 20-50% to surface concentrations depending on the species. This indicates that pollution control efforts should take a regional perspective. Air quality projections in Delhi for 2030 are investigated. The Greenhouse Gas and Air Pollution Interactions and Synergies (GAINS) model is used to generate a 2030 future emission scenario for Delhi using projections of air quality control measures and energy demands. Net reductions in CO concentrations by 50%, and increases of 140% and 40% in BC and NOx concentrations, respectively, are predicted. The net changes in concentration are associated with increases in transport and industry sectors. The domestic sector still has a significant contribution to air pollutant levels. The air quality levels show a profound effect under this scenario on the environment and human health. The increase in pollution from 2010 to 2030 is predicted to cause an increase in surface temperature by ~0.65K. These increasing pollution levels also show effects on the radiative forcing. The high aerosols loading i.e. BC, PM2.5 and PM10 levels show strong influence on the short and longwave fluxes causing strong surface dimming and strong atmosphere heating due to BC. These results indicate transport and domestic sectors should be targeted for air quality and climate mitigations.

Let G be an undirected graph on n vertices and let S(G) be the class of all real-valued symmetric n × n matrices whose nonzero off-diagonal entries occur in exactly the positions corresponding to the edges of G. Let V = {1, 2, . . . , n} be the vertex set of G. A scheme on G is a function f : V → {0, 1}. Given a scheme f on G, there is an associated class of matrices Sf (G) = {A ∈ S(G)|aii = 0 if and only if f(i) = 0}. A scheme f is said to be constructible if there exists a matrix A ∈ Sf (G) with rank A = min{rank M|M ∈ S(G)}. We explore properties of constructible schemes and give a complete classification of which schemes are constructible for paths and cycles. We also consider schemes on complete graphs and show the existence of a graph for which every possible scheme is constructible.

<p>The Earth's atmosphere is expected to warm in response to increasing atmospheric concentrations of greenhouse gases (GHG). The response of the Earth's complex and chaotic climate system to the GHG emissions is, however, difficult to assess. In this thesis, two issues of importance for the assessment of this response are studied. The first concerns the magnitude of the natural and anthropogenic emissions of CO₂. An atmospheric transport model is used, combined with inventories of anthropogenic CO₂ emissions and estimates of natural emissions, to compare modelled and observed variations in the concentration of CO₂ at an Arctic monitoring site. The anthropogenic and natural emissions are shown to exert approximately equal influence on Arctic CO₂variations during winter.</p><p>The primary focus of this thesis is the response of the climate system to the enhanced GHG forcing. It has been proposed that this response may project onto the leading modes of variability. In the present thesis, this hypothesis is tested against the alternative that the spatial patterns of variability change in response to the enhanced forcing. The response of the atmospheric circulation to the enhanced GHG forcing as simulated by a specific coupled global climate model (CGCM) is studied. The response projects strongly onto the leading modes of present-day variability. The spatial patterns of the leading modes are however changed in response to the enhanced GHG forcing. These changes in the spatial patterns are associated with a strengthening of the waveguide for barotropic Rossby waves in the Southern Hemisphere. The Northern Hemisphere waveguide is however unchanged.</p><p>The magnitude of the global mean responses to an enhanced GHG forcing as simulated by CGCMs vary. Moreover, the regional responses vary considerably among CGCMs. In this thesis, it is hypothesised that the inter-CGCM differences in the spatial patterns of the response to the enhanced GHG forcing are partially explained by inter-CGCM differences in zonal-mean properties of the atmospheric flow. In order to isolate the effect of these differences in the zonal-mean background state from the effects of other sensitivities, a simplified model with idealised forcing is employed. The model used is a global three-level quasi-geostrophic model. The sensitivity of the stationary wave pattern (SWP) to changes in the zonal-mean wind and tropopause height of similar magnitude as those found in response to the enhanced GHG forcing in CGCMs is investigated. The SWP in the simplified model shows a sensitivity of comparable magnitude to the analogous response in CGCMs. These results indicate that the CGCM-simulated response is sensitive to relatively small differences in the zonal-mean background state. To assess the uncertainties in the regional response to the enhanced forcing associated with this sensitivity, ensemble simulations of climate change are of great importance.</p>