Since Texas normally receives most of its precipitation in the warm season, precipitation deficits in summertime may bring serious agricultural and hydrological disasters. While the underlying physical processes of summer precipitation deficit and drought are unclear, they can be understood in terms of convective instability. This research is designed to investigate how convective instability influences monthly mean precipitation in Texas in the summertime and to examine the modulation of convective instability and precipitation by upper-level circulations, soil moisture, vertical motion, and low-tropospheric warm air transport using NCEP/NCAR reanalysis data. Statistical approaches including correlation analysis, multiple linear regression analysis and back trajectory analysis were used to reveal the underlying dynamics of their linkage and causality. The results show that warming at 700 mb and surface dryness result in excessive convective inhibition (CIN), leading to precipitation deficits on a monthly time-scale. Temperature at 700 mb (Tlt) and surface dewpoint have little correlation suggesting different processes contribute to warming at 700 mb and surface dryness, respectively. Correlation analysis among the surface variables emphasizes the role of soil moisture on the dewpoint and thermodynamics at the surface. Back trajectory analysis indicates that a significant contributor to warming at 700 mb is the inversion caused by warm air transport from the Rocky Mountains and the Mexican Plateau where the surface potential temperature is greater than 307.5K rather than by subsidence. It was found that downward motion and warm air transport are enhanced in Texas when upper-level anticyclonic circulation develops in the southern US. Upper-level anticyclonic circulations in the southern US strongly affect Texas summertime precipitation by modulating the principal processes as follows. They increase CIN not only by enhancing warm air transport from the high terrain but also by suppressing occurrence of disturbances. The resulting reduced precipitation and dry soil significantly modulate surface conditions, which elevates CIN and decreases precipitation. The aforementioned chain-reaction of upper-level anticyclone influences can be understood in the context of CIN.

Since Texas normally receives most of its precipitation in the warm season, precipitation deficits in summertime may bring serious agricultural and hydrological disasters. While the underlying physical processes of summer precipitation deficit and drought are unclear, they can be understood in terms of convective instability. This research is designed to investigate how convective instability influences monthly mean precipitation in Texas in the summertime and to examine the modulation of convective instability and precipitation by upper-level circulations, soil moisture, vertical motion, and low-tropospheric warm air transport using NCEP/NCAR reanalysis data. Statistical approaches including correlation analysis, multiple linear regression analysis and back trajectory analysis were used to reveal the underlying dynamics of their linkage and causality. The results show that warming at 700 mb and surface dryness result in excessive convective inhibition (CIN), leading to precipitation deficits on a monthly time-scale. Temperature at 700 mb (Tlt) and surface dewpoint have little correlation suggesting different processes contribute to warming at 700 mb and surface dryness, respectively. Correlation analysis among the surface variables emphasizes the role of soil moisture on the dewpoint and thermodynamics at the surface. Back trajectory analysis indicates that a significant contributor to warming at 700 mb is the inversion caused by warm air transport from the Rocky Mountains and the Mexican Plateau where the surface potential temperature is greater than 307.5K rather than by subsidence. It was found that downward motion and warm air transport are enhanced in Texas when upper-level anticyclonic circulation develops in the southern US. Upper-level anticyclonic circulations in the southern US strongly affect Texas summertime precipitation by modulating the principal processes as follows. They increase CIN not only by enhancing warm air transport from the high terrain but also by suppressing occurrence of disturbances. The resulting reduced precipitation and dry soil significantly modulate surface conditions, which elevates CIN and decreases precipitation. The aforementioned chain-reaction of upper-level anticyclone influences can be understood in the context of CIN.

Palaeoclimate reconstruction is of paramount importance because the more we know about the patterns of past variability the better we understand the present climate. Precipitation is a key climate variable shaping the culture and economy of China. However, few studies are concerned with past changes in precipitation. The existing few are either reconstructed by one reconstruction approach or based on a single proxy, limiting reconstructions to a small region and a short period of time. The study presents the first high-resolution multi-proxy palaeoprecipitation reconstruction of China as a whole. Proxies used in the study are of annual-to-decadal resolution, mainly including historical written evidence, tree-ring chronologies and stable isotopic records. In accordance with the principle of “uniformity in the nature”, about 80 proxy series extend the precipitation records as far back in time as 2,000 years ago when there was a significant increase in natural proxy and documentary records of climate all over China. The top three popular reconstruction approaches are borrowed from multi-proxy temperature reconstructions to reconstruct the palaeoprecipitation. A pioneering attempt is taken to evaluate and compare these approaches in reconstructing precipitation over a long term in a large scale. The three common practices are respectively simple average, composite-plus-scale method, and covariance-based climate field reconstruction. All three reconstruction methods are modified catering to the unique characteristics of precipitation, especially in terms of its large spatial variance. Local reconstructions are carried out first before a national index in reconstructed. Though based on the same documentary and natural proxies, three reconstruction approaches adopt different rationales to decipher the precipitation variability, represented by different statistical models. Each model is assessed by conventional statistics and cross-compared. These models are found complementary to each other while the common shared among three models are considered the closest to the true precipitation condition. Though geographically biased to Eastern China, historical documents still capture the most inter-annual to multi-centennial variations in palaeoprecipitation, indicating the possible control of Asian Monsoon climate on China’s overall precipitation. Tree-ring widths preform worst due in part to the attribute of strong locality. Each reconstruction approach turns out to have its own strength and weakness. Three major falls at multi-centennial timescale are detected in most reconstructed precipitation series, which are at AD600-800, AD1000-1300 and AD1500-1700. Spectral analyses demonstrate a rhythmic pattern of around 400-500 years for all reconstructions. When the proxies are not extrapolated, an additional cycle of 700-800 years is significant in precipitation variability over the past 2,000 years. A cross-comparison with European reconstructions show a high agreement in precipitation variability for the past two millennia, leading to the suspect of dry Medieval Warm Period and wet Little Ice Age over the whole Eurasia. / published_or_final_version / Geography / Master / Master of Philosophy

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Kwang-Yul Kim, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed Sept. 24, 2004). Includes bibliographical references.

Thesis (M.S.)--Florida State University, 2006. / Advisor: Kwang-Yul Kim, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed June 13, 2006). Document formatted into pages; contains x, 69 pages. Includes bibliographical references.

Monthly and annual changes in precipitation in South China during 1990-2011 are examined in this study. As located in the sub-tropical climate zone, the annual rainfall in South China is concentrated in the summer. During the same period of time, an average of 9 tropical cyclones approaching South China each year which also contribute ample of rainfall to South China during the tropical cyclone season (June-September). Since the climatic system is interconnected, so this study attempts to examine the combined effect on inter annual rainfall variations in South China due to El Nino Southern Oscillation (ENSO), tropical cyclones affecting South China and the Asian Monsoon. It is generally agreed that during the El Nino onset years, South China would be more wetter, but with less than average tropical cyclones affecting South China. As such, effects on precipitation in South China caused by these two factors offsetting each other and data indicate there is no consistent trend of either more or less rainfall recorded for the El Nino onset years during 1990-2011. On the other hand, the first half of the year right after the El Nino years are in general more wetter than normal. This can be due to the lagging effect of El Nino events normally happened in the winter time, plus the fact that the strength of winter monsoon during the El Nino years is weak, resulting in more rainfall in the following year. Furthermore, annual changes in precipitation in South China directly affect the surface runoff of the Pearl River and a strong positive correlation between the two variables exists for the period 2000-2011. The +/- 25% annual variations and the seasonal variations of rainfall in South China post a challenge to the water resource management in the Pearl River Delta Region. Therefore dams and reservoirs built along the Pearl River are necessary to store surplus rainwater in order to supply sufficient fresh water to the Pearl River Delta Region during the dry seasons or years. On the other hand, further studies and monitoring programs are recommended to continue assessing and evaluating impacts of dam constructions to the environment and the ecosystem of the Pearl River Delta Region. / published_or_final_version / Applied Geosciences / Master / Master of Science

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Atmospheric Science." Includes bibliographical references (p. 98-108).

Thesis (Ph. D.)--University of Canterbury, 2009. / Typescript (photocopy). Includes bibliographical references (p. 214-243). Also available via the World Wide Web.

Resumo: O objetivo deste trabalho foi analisar as variabilidades espacial, sazonal e interanual da precipitação pluviométrica nas regiões Sudeste e Sul do Brasil. Foram utilizadas 164 séries mensais e anuais de chuvas para o período de 1972 a 2002 e dados de médias mensais de radiação de ondas longas emergentes (ROLE), para o período de junho de 1974 a dezembro de 2002, com pontos de grade com resolução espacial de 2,5º x 2,5º, entre as latitudes 20ºN e 35ºS e longitudes entre 0º; 90ºW. A partir das análises de agrupamento, de componentes principais e geoestatística foram identificadas 13 regiões homogêneas de regime de precipitação. A precipitação anual variou de 956 mm nos vales do São Francisco- Jequitinhonha a 1830 mm na Bacia do Iguaçu-Chapecó. As três primeiras componentes principais (CP) da matriz de médias mensais de precipitação explicam conjuntamente, 61,49% da variância. A primeira CP representa o campo médio de precipitação, a segunda CP representa o período de verão e a terceira CP apresenta dois pontos extremos: o mês de novembro e o mês de fevereiro. Através dos dados de ROLE analisou-se a influência da Zona de Convergência do Atlântico Sul (ZCAS) na precipitação. As três primeiras componentes principais da matriz de médias mensais de ROLE explicam conjuntamente 96,27% da variância. A primeira CP representa a convecção média. A segunda CP representa o período de primavera e a terceira CP representa o período de verão. As correlações, significativas ao nível de 5%, obtidas entre os autovetores das matrizes de precipitação pluviométrica e de ROLE, corroboram a influência da ZCAS no regime de precipitação das regiões Sudeste e Sul do Brasil. / Abstract: The spatial, seasonal and interannual variability of rainfall in Southeastern and Southern Brazil were analyzed. For that, 164 series of rainfall for the period of 1972 to 2002 and data about outgoing longwave radiation (OLR) for the period of 1974 to 2002 were utilized. From the clusters analysis and components analysis (PCA), 13 homogeneous regions under precipitation regime were identified. The annual rainfall varied from 956 mm in São Francisco-Jequitinhonha valleys to 1830 mm in Iguaçu-Chapecó basin. The three first matrix principal components (PC) of monthly average rainfall (average of 30 years) explain together 61.49% of the variance. The first PC represents the mean rainfall field, the second PC represents the extended rainy period (September to May) and the third PC presents two extreme points: November indicates the end of spring and the beginning of summer; and February indicates the end of summer and the beginning of autumn. The OLR influence on the rainfall variability in the Southeast and in the South was also evaluated. Through the PCA, the behavior of the South Atlantic Convergence Zone (SACZ) was studied together with its influence on the rainfall variability. The three first matrix main components of OLR monthly average (average of 30 years) explain together 96.27% of the variance. The first main component (CP) is associated to the period of autumn. The second PC represents the winter/summer period, and the third PC represents summertime. The correlations, significative to the level of 5%, obtained between the rainfall and OLR eigenvectors, attest their influence on the rainfall regime in Southeastern and Southern Brazil. / Orientador: Luzia Aparecida Trinca / Coorientador: Jonas Teixeira Nery / Banca: Angelo Cataneo / Banca: João Francisco Escobedo / Banca: Shigetoshi Sugahara / Banca: Paulo Henrique Caramori / Doutor

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 170-178). Also available for download via the World Wide Web; free to University of Oregon users.