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This study addresses the availability of total solar irradiance at the earth's surface during varying weather conditions . Two years of irradiance and meteorological data were collected at mountain and valley sites along 40° North latitude in the Rocky Mountains of Utah and Colorado. Generalized cases of recurring seasonal weather episodes and the associated t o t al irradiance a re identified and discussed , including local mesoscale phenomena (orographic clouds , valley fog, etc.) unique to mountainous regions . The generalized cases can be useful in long- range energy assessment planning. The east and west slopes of the Rocky Mountains are shown to have similar annual average solar energy potential , however the seasonal differences reveal unique climates which require different considerations for each slope. Short -term relationships between cloudiness and t o t al irradiance are developed for the mountainous region, providing a tool for forecasting solar irradiance using a cloudiness forecast. Total irradiance is shown to correlate much better to opaque sky cover than co total cloud cover . The relationships on the east and west slopes are similar , however greater variations a re observed with elevation between the moun t ain and valley sites . Short- term forecasting of irradiance is found to be limited due t o unreliable cloudiness fore-casting techniques , tho ugh satellite imagery trajectories are more reliable than numerical methods.

Cut-Off Lows (COLs) are certainly amongst the most important synoptic-scale rain producing weather systems in South Africa. Rainfall associated with COLs is usually widespread, while about 20% of COLs are associated with heavy rainfall. Both these attributes of rainfall associated with COLs are important to agriculture. Widespread rainfall secures good grazing potential, while heavy rainfall not only contributes largely to maintaining dam levels that are needed for irrigation, but also to flooding and erosion. Agriculture in the Eastern Cape Province of South Africa is predominantly rain-fed, while agricultural activities that depend on irrigation are mostly located along the western coastal belt of the province. Despite of the fact that all COLs do not pass directly over the Eastern Cape Province, most of them appear to have a direct or indirect influence on the rainfall of the province, and in turn, impact on agricultural production and even the economy. In this study, the contribution of COLs to rainfall over the Eastern Cape Province is investigated. In order to achieve this, a climatology of COLs for the period 1979 to 2009 (31 years) was constructed by utilizing the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis data to create 6-hourly contour images of geopotential heights and air-temperatures at the 500 hPa pressure level. All COLs that occurred over South Africa bounded by 200S to 400S and 00E to 500E from the day they started (at the formation of a closed low pressure system) until the day they ended (at the disappearance of the closed low pressure system), and that were cold cored, were considered as potential COLs in this study. In addition, low level circulation maps obtained from the South African Weather Service’s (SAWS’s) daily weather bulletins were used to ensure that the defined COLs were indeed extending from the 500 hPa pressure level to the land surface. Daily rainfall totals from 22 well-distributed weather stations over the Eastern Cape Province were used to determine the contribution of COLs to the rainfall over the province. It was found that 64% of COLs that lasted for more than 24-hours over the study domain had an influence on the total rainfall over the Eastern Cape Province. Monthly frequency distribution of COLs reveal that April and May had the highest occurrences, while December and January have the least occurrence. Long-term seasonal frequencies distributions of COLs show the highest occurrence during March-April-May (MAM) with the least occurrences during December-January-February (DJF). Most COLs lasted for 2-4 days over South Africa and the Eastern Cape Province for the study period of 31-years. The contribution of rainfall associated with the occurrence of COLs is found to be approximate 37-38% annually along the coastal areas, while it is less than 10% annually over the interior of the Eastern Cape Province. / MSc / gm2014 / Geography, Geoinformatics and Meteorology / unrestricted

Made available in DSpace on 2014-08-20T14:25:49Z (GMT). No. of bitstreams: 1 dissertacao_morgana_silva.pdf: 2722474 bytes, checksum: 9da7b789c8c0d3445e96692ab0d15b82 (MD5) Previous issue date: 2010-02-11 / The Water regime of a region is determined by the availability of soil water (both deficiency and excess) that can be estimated with acceptable accuracy using variables such as precipitation (entry of water into the ground) and evapotranspiration (output of water from the soil) through a system of water balance. The aim of this study was to determine and analyze the seasonal climatological water balance in the northern half and southern half of Rio Grande do Sul (RS) from 1977 to 2006, as RS has had a significant spatial variability of annual precipitation since in the southern half is lower than the Northern Half of the state. Specifically, it was analyzed the impact of weather systems on the water regime of RS in 2006. It has been used for the calculation of water balance, monthly data of average temperature and precipitation from 1977 to 2006, which was obtained from the National Institute of Meteorology - INMET (8th District of Meteorology) from 16 meteorological stations located in different ecoclimatic regions of the state. To calculate the water balance it was been used the method proposed by Thornthwaite and Mather (1955) and to calculate the evapotranspiration, the method of Thornthwaite (1948) was used the data from Bulletins of Climate Analysis from database of civil defense of RS and satellite images GOES-12 (Geostationary Operational Environmental Satellite) provided by the Center for Weather Forecasting and Climate Studies located at the National Institute for Space Research - CPTEC / INPE. The results for the study period (1977 to 2006) showed that the distribution of precipitation in RS was fairly uniform across the four periods of the year with record volumes of rainfall in the northern half of the state. It may be noted that the North Half of RS has presented over water throughout the year due to higher rainfall associated with lower evaporative rates. In the south, water deficits in JFM and OND has been observed, but these have been less than the excess water, so there is lack of water. In 2006 the northern half of RS, lack of water has not occurred, despite the occurrence of water deficits in the quarters of JFM, AMJ and OND. In the southern half in 2006, the reduced availability of water and increased water stress in relation to normal conditions have caused water shortages in JFM and OND on the coast. Factors that contributed to the occurrence of excess water above the water deficit during 2006 in the North Half and water shortages in the south of RS in JFM and OND on the coast, have been: highest frequency of Weather and Climate System event with severe weather conditions in the northern half of RS related to the southern half; the lowest frequency of Frontal System this year in the south of RS related to the climate normal period from 1977 to 2006 and the role of ENSO whose configuration in 2006 led to drought in southern Brazil, and therefore precipitation below normal in all quarters year. / O regime hídrico de uma região é determinado pela disponibilidade de água no solo (deficiência ou excesso), que pode ser estimada com aceitável precisão, utilizando variáveis como precipitação (entrada de água no solo) e evapotranspiração (saída de água do solo), através de um sistema de balanço hídrico. Como o Rio Grande do Sul (RS) apresenta uma variabilidade espacial significativa de precipitação anual, uma vez que na Metade Sul é inferior à da Metade Norte do Estado, o objetivo geral deste trabalho foi determinar e analisar sazonalmente os balanços hídricos climatológicos (BHC) para a Metade Norte e Metade Sul do RS, no período de 1977 a 2006. Mais especificamente, pretendeu-se analisar o impacto dos sistemas meteorológicos (SM) no regime hídrico do RS no ano de 2006. Foram utilizados, para o cálculo dos BH, dados mensais de temperatura média e precipitação pluvial do período de 1977 a 2006, obtidos no Instituto Nacional de Meteorologia - INMET (8° Distrito de Meteorologia) de 16 estações meteor ológicas distribuídas nas diferentes regiões ecoclimáticas do Estado. O método proposto por Thornthwaite e Mather (1955) foi utilizado para calcular os BHC e para calcular a evapotranspiração utilizou-se o método de Thornthwaite (1948). Para a análise do impacto dos SM no regime hídrico do RS no ano de 2006 utilizaram-se dados obtidos nos Boletins Climanálise, no banco de dados da defesa civil do RS e imagens do satélite GOES- 12 (Geostationary Operational Environmental Satellite) fornecidas pelo Centro de Previsão de Tempo e Estudos Climáticos do Instituto Nacional de Pesquisas Espaciais CPTEC/INPE. Os resultados para o período de estudo (1977 a 2006) mostraram que a distribuição de precipitação no RS foi bastante uniforme nos quatro períodos do ano, com registro de maior volume pluviométrico na Metade Norte do Estado. Observou-se que a Metade Norte do RS apresenta excesso hídrico durante todo ano, devido aos maiores índices pluviométricos associados a menores índices evaporativos. Já na Metade Sul foram observados déficits hídricos em JFM e OND, mas estes foram inferiores aos excessos hídricos, portanto não ocorre falta de água. Em 2006 na Metade Norte do RS não ocorreu falta de água, apesar da ocorrência de déficits hídricos nos trimestres de JFM, AMJ e OND, uma vez que estes foram inferiores aos excessos hídricos. Na Metade Sul, em 2006, a menor disponibilidade de água e a maior deficiência hídrica em relação às condições normais, causaram falta de água em JFM e o no litoral em OND. Os fatores que contribuíram para a ocorrência de excedentes hídricos superiores aos déficits hídricos durante o ano de 2006 na Metade Norte e falta de água na Metade Sul do RS em JFM e no litoral em OND, foram: a maior frequência de sistemas convectivos de mesoescala (SCM) e de eventos com condições de tempo severo na Metade Norte do RS em relação à Metade Sul; a menor frequência de SF neste ano na Metade Sul do RS em relação à normal climatológica do período de 1977 a 2006 e a atuação do fenômeno ENOS cuja configuração em 2006 provocou estiagem na região sul do Brasil e, portanto precipitação abaixo da normal em todos os trimestres do ano.