<p>While very important from an economical and societal point of view, estimating precipitation in the western United States remains an unsolved and challenging problem. This is due to difficulties in observing and modeling precipitation in complex terrain. This research examines this issue by (i) providing a systematic evaluation of precipitation observations to quantify data uncertainty and (ii) investigating the ability of the Ocean-Land-Atmosphere Model (OLAM) to simulate the winter hydroclimate in this region. This state-of-the-art, non-hydrostatic model has the capability of simulating simultaneously all scales of motions at various resolutions.</p><p>This research intercompares nine precipitation datasets commonly used in hydrometeorological research in two ways. First, using principal component analysis, a precipitation climatology is conducted for the western U.S. from which five unique precipitation climates are identified. From this analysis, data uncertainty is shown to be primarily due to differences in (i) precipitation over the Rocky Mountains, (ii) the eastward wet-to-dry precipitation gradient during the cold season, (iii) the North American Monsoon signal, and (iv) precipitation in the desert southwest during spring and summer. The second intercomparison uses these five precipitation regions to provide location-specific assessments of uncertainty, which is shown to be dependent on season and location.</p><p>Long-range weather forecasts on the order of a season are important for water-scarce regions such as the western U.S. The modeling component of this research looks at the ability of the OLAM to simulate the hydroclimate in the western U.S. during the winter of 1999. Six global simulations are run, each with a different spatial resolution over the western U.S. (360 km down to 11 km). For this study, OLAM is configured as for a long-range seasonal hindcast but with observed sea surface temperatures. OLAM precipitation compares well against observations, and is generally within the range of data uncertainty. Observed and simulated synoptic meteorological conditions are examined during the wettest and driest events. OLAM is shown to reproduce the appropriate anomaly fields, which is encouraging since it demonstrates the capability of a global climate model, driven only by SSTs and initial conditions, to represent meteorological features associated with daily precipitation variability.</p> / Dissertation

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 2001. / Includes bibliographical references.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references. Also available in electronic version. Access restricted to campus users.

Inaug.-diss.--Göttiagen. / Lebenslauf. Folds of table numbered as p. 13-16. Includes bibliographical references.

Thesis (M.S. in Combat Systems Technology)--Naval Postgraduate School, December 2003. / Thesis advisor(s): D.L. Walters, D.K. Miller. Includes bibliographical references (p. 35-36). Also available online.

Thesis--M. Phil., University of Hong Kong, 1978.

Thesis (Ph. D.)--California Institute of Technology, 1988. UM #88-03,381. / Advisor names found in the Acknowledgments pages of the thesis. Title from home page. Viewed 02/19/2010. Includes bibliographical references.

The phase of atmospheric particles can influence heterogeneous chemistry, cloud formation, and radiative forcing. Sulfate particles ranging from sulfuric acid to ammonium sulfate are the largest contributor arising from anthropogenic activities to the global fine aerosol burden. Multi-component inorganic particles of neutralized or partially neutralized crystalline components and acidic solutions can form via uptake of gaseous ammonia. Under some atmospheric conditions, secondary organic material can combine with sulfate species to form internally mixed organic-sulfate particles. The way in which interactions between the constituents in ambient multi-component particles affect the phase of the overall particle are not well understood, especially for complex mixtures containing secondary organic material. This thesis presents measurements of relative humidity-dependent phase transitions of atmospherically relevant multicomponent particles, measured using tandem differential mobility analyzer (TDMA) setups. Particle morphologies implied by these measurements and their impact on other atmospheric processes are discussed. The connection between particle morphology and hygroscopic phase transitions is first discussed in the context of internally mixed ammonium bisulfate and letovicite particles. Unexpected differences in the deliquescence behavior of individual particles of identical diameter and overall composition were observed. From the deliquescence data, we hypothesized composition- and diameter-dependent morphologies based on heterogeneous crystallization of the particles that explained the variable water uptake and deviations from thermodynamic predictions of deliquescence. In multi-component particles containing both organic and inorganic material, phase separation can occur in addition to the deliquescence and efflorescence transitions. The phase transitions and hygroscopic growth of particles composed of ammonium sulfate mixed with secondary organic material are presented and interpreted in a morphological context. Secondary organic material was generated in the Harvard Environmental Chamber via the photo-oxidation of isoprene, the ozonolysis of \(\alpha\)-pinene, and the photo-oxidation of \(\alpha\)-pinene. The occurrence of liquid-liquid phase separation between aqueous ammonium sulfate and \(\alpha\)-pinene-derived organic material, not directly observable from hygroscopic growth measurements, was inferred from the minimal influence of the organic material on the ammonium sulfate phase transitions (less than 4% RH deviation from pure ammonium sulfate values). In contrast, the influence of isoprene photo-oxidation products on the phase transitions of ammonium sulfate was substantial: Both the deliquescence relative humidity and the efflorescence relative humidity of the mixed particles were decreased by over 30% RH from pure ammonium sulfate values for high organic volume fraction. These results implied that dissolved ammonium sulfate, organic molecules, and water were mixed in a uniphasic solution. The dependence of secondary organic material phase on relative humidity and growth factor was investigated via concurrent measurements of particle bounce and hygroscopic growth. Particles were composed of ammonium sulfate mixed with the products of isoprene photo-oxidation, \(\alpha\)-pinene ozonolysis, or \(\alpha\)-pinene photo-oxidation. Particle bounce gradually decreased as RH was increased. The bounce behavior of all three types of particles were closely correlated with growth factor. These results implied that the uptake of particle-phase water caused gradual softening of the particles. / Engineering and Applied Sciences

Atmospheric aerosols and trace gases are a highly relevant component of the climate system affecting atmospheric radiative transfer and the hydrologic cycle. In arid and semi-arid regions, where cloud cover is often low and precipitation is generally scarce and sporadic, the driving processes accounting for the production, loss and transport of atmospheric constituents are often distinctly different from other climates. In arid regions, the same circulation dynamics that suppress cloud formation can be responsible for creating strong subsidence inversions, which cap atmospheric mixing and trap pollutants close to the surface, often placing populated arid regions high on global rankings of air pollution concerns. In addition, low soil moisture can encourage wind-blown dust emissions, which can be a significant fraction of the total aerosol loading in both coarse and fine modes on a mass basis. Three distinct focus regions are investigated over varying time scales, using a diverse set of techniques, and with wide-ranging primary goals. 1) the Tehran metropolitan area in Iran over a ten-year period from 2000-2009, 2) Tucson, Arizona over 2012-2014 with three intensive monitoring periods during summer 2014 and winter 2015 and 3) the San Joaquin Valley in California during the NASA DISCOVER-AQ campaign during Jan-Feb 2013. However, in all cases, local and regional scale meteorology play a significant role in controlling the spatiotemporal variability in trace gas and aerosol concentrations. Particular emphasis is placed on understanding transport pathways due to the local wind patterns and the importance of key meteorological parameters such as temperature, humidity and solar radiation on controlling production and loss mechanisms. While low in magnitude, the precipitation pattern is still an important sink mechanism that modulates gas phase and particle abundances in all three regions, either through scavenging or by promoting vertical mixing. The reported measurements and data analysis serve to improve the characterization of trace gases and aerosols in populated arid regions and offer process level understanding of dominant mechanisms for model validations and improvements.

No description available.