Thesis (Ph. D.)--Ohio State University, 2003. / Title from first page of PDF file. Document formatted into pages; contains xvii, 147 p.: ill. Includes abstract and vita. Advisor: David H. Bromwich, Dept. of Geography. Includes bibliographical references (p. 140-147).

Thesis (M.A. in National Security Affairs)--Naval Postgraduate School, June 2003. / Thesis advisor(s): David S. Yost, Mikhail Tsypkin. Includes bibliographical references. Also available online.

This work represents an analysis of the spatial and temporal variability of nitrate deposition and preservation recorded in multiple ice core and snow pit records from the Greenland ice sheet. The primary objective of this research was to develop improved estimates of variability in the preserved ice core record of nitrate to aid in the interpretation of paleoatmospheric concentrations of reactive nitrogen compounds. Three separate works are presented, each focusing on a unique component of variability. The first is a study related to the direct preservation of nitrate over a single year. The second and third topics are related to analysis of ice core records collected during NASA's Program for Arctic Regional Climate Assessment (PARCA) which was initiated in 1993 and continued through 2002.The first study of preservation demonstrated that nitrate, despite possible post-depositional cycling and alteration, was well preserved throughout the year, such that the total flux measured in a snow pit taken to represent the previous year, was representative of snow surface concentrations during the past year. The small difference in preserved concentrations from observed surface snow concentrations gives evidence of only 7% post-depositional loss at this site (mean annual accumulation ~23 g cm-2 yr-1). Results from these studies indicate that at this site accumulation is the most significant process affecting preservation of nitrate in the firn.In the second study, the temporal variability of preserved nitrate was evaluated through time series analysis and correlation studies with available paleoclimate proxy records. Six Greenland ice cores covering the period 1794-1995 show correlated co-variability of nitrate concentration for periods greater than ten years and a ~60% increase in average concentration during the last 75 years. The changes in concentration yield ~30% higher nitrate flux (2.5 to 3.2 g m-2 a-1) and ~11% greater variability during 1895-1994 period versus the prior 100 years. Nitrate trends in the cores during the last 100 years are also correlated with global nitrate emissions, with an average r-value of 0.93 for the six cores.The last study focused on spatial variability of nitrate, and the relation of deposition to components of the earth system including temperature and accumulation. The objective of the study was to assess the contribution of spatial (latitude, longitude, and elevation) and climate (accumulation and temperature) components to the preserved record. Furthermore, the study evaluated the influence of anthropogenic activities on the spatial distribution of nitrate of the Greenland ice sheet. Large scale spatial variability exists as a result of accumulation gradients, with concentration 5% greater in the northern plateau, yet flux over the northern plateau is 30% lower than the dry snow zone as a whole. While spatially, flux appears to be more dependent on accumulation, preservation of flux shows increasing dependence on concentration with increasing accumulation. The relationship between concentration and accumulation is non-linear, showing less dependence in the low accumulation regions versus high accumulation regions. Accumulation alone is insufficient to account for the observed variability in nitrate flux in the low accumulation regions, and evidence supports an additional component to a transfer function model for nitrate that includes photochemistry, temperature, and possibly sublimation. In high accumulation regions, evidence points to a dilution effect, with concentration decreases resulting from increased accumulation. Flux estimates over the ice sheet are compared with a GEOS-CHEM model estimate of reactive nitrogen vertical fluxes showing the model captures a significant component of the variability in the southern portion of the ice sheet, but under-represents the flux and variability in the northern half of the ice sheet by a factor of 4.

The Arctic Oscillation (AO) and the North Atlantic Oscillation (NAO) are the most pronounced modes of extratropical atmospheric wintertime variability in the Northern Hemisphere. This thesis investigates different aspects of the AO and NAO on the in traseasonal and seasonal time scales. First, the question of how the differences between the AO and NAO are influenced by the choice of the definitions of the NAO and to what extent the AO and NAO differ from each other is investigated using the daily NCEP/NCAR reanalysis data spanning 51 boreal winters. One AO index and four different NAO indices are used in this study. It is found that the AO and NAO are quite similar to each other when both are defined using pattern-based indices, while some notable differences are observed between them when the NAO is defined using a station/gridpoint-based index. Then the predictability of the AO and NAO is examined using a simple general circulation model (SGCM). Numerical experiments are performed to determine the sensitivity of the setup processes of the AO and NAO to the details of the initial conditions. The predictive skills for the AO and NAO are compared to each other. Finally, the potential role of tropical Pacific forcing in driving the seasonal variability of the AO is explored using both observations and the SGCM. The results indicate that a negative thermal forcing over the western tropical Pacific and a positive forcing north of the equatorial mid-Pacific play important roles in producing an AO-like atmospheric response.

The mean dynamic topography (MDT) of the ocean is closely related to the mean surface circulation. The objective of this thesis is to produce estimates of the MDT for the North Atlantic using newly available data from ocean and gravity observing systems, to evaluate these new estimates and so improve our understanding of the circulation. Oceanographic estimates of the MDT are based on the mean temperature and salinity (TS) fields of the ocean. These are typically averages from sparse observations collected over many decades. The ocean is a non-stationary system so it is more appropriate to define the mean for shorter, specific periods. Whilst the Argo observing system has increased the frequency and resolution of in situ oceanographic measurements, high frequency (eddy) variability remains. A new technique is described for removing this variability using satellite altimeter measurements of the sea surface height. A new TS mean is produced, relating to the period from 2000 to 2007, and this is used to map a new oceanographic estimate of the MDT using an ocean circulation model. New geodetic estimates of the MDT are produced using geoid models that incorporate gravity measurements from the ongoing GRACE and GOCE satellite missions. These are compared with the new oceanographic estimate and validated against independent observations such as drifter speeds. The geodetic method produces realistic estimates of the mean surface circulation, thereby realizing the long time dream of oceanographers to observe the ocean circulation from space. The new oceanographic estimates are not as accurate, but the new TS mean contributes to improvements in the performance of ocean models, a necessary step in understanding and predicting the oceans. Coastal tide gauges can provide an accurate estimate of the alongshore tilt of the coastal MDT and this has been used to evaluate the above estimates. Temporal variability of the tilt along the coast of the South Atlantic Bight is used, with statistical methods and an ocean circulation model, to identify the processes contributing to the tilt. A new opportunity to use tide gauges as part of an observing system for the ocean circulation is discussed.

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Hydrographic data, in the time range from 1908 to 2006, extracted from the International Council for the Exploration of the Sea (ICES) database, are used to examine variability of water masses in the North Atlantic ocean along 38N. All the data are interpolated in an ideal isopycnal framework, which has a longitudinal resolution of 1/3 degree and 50 isopycnal layers of variable thickness, to 38N by using an objective analysis approach. A 5 year-running mean triad analysis is performed from 1950 to 2004 for further variability study. Extensive decadal to inter-decadal variability is observed, in both shallow and deep layers. In the deep layers, a signal of westward phase propagating is detected, coincided with the time scale of a first mode baroclinic Rossby wave transporting at this latitude. Strong negative correlations (maximum at a lag of 7 years) are seen between the variability in the DWBC and the North Atlantic Oscillation. A similar correlation at the same lag is also detected in the basin interior, suggesting the Labrador Sea Water (LSW) pathway is not only restrained to the DWBC.

Diss. Stockholm : Stockholms universitet, 2007.