This study investigates modes of atmospheric variability in response to changes in Earth's orbit and changes in 20th century sea surface temperatures (SST). The orbital forcing is manifested by a change in obliquity and precession, and changes the distribution of the top-of-atmosphere insolation. A smaller obliquity reduces the the annual insolation that the poles receive and increases the annual insolation in the tropics. As the meridional insolation gradient increases, the zonal mean atmospheric-ocean circulation increases. The resulting climate also has a reduced global mean temperature due to the effect of climate feedbacks. This cooling can be attributed to a reduced lapse rate, increased cloud fraction. reduced water vapor in the atmosphere, and an increase in the surface albedo. A change in the precession, as the perihelion shifts from the winter to the summer solstice, causes a strengthening as well as an expansion of the N. Pacific summer subtropical anticyclone. This anticyclonic anomaly can be attributed to the weakening of the baroclinic activity, but also represents the circulation response to remote and local diabatic heating. The remote diabatic heating is associated with monsoonal activity in the SE Asia and North Africa. Regarding the 20th century SST forcing, it is represented by a multidecadal variability in the inter-hemispheric SST difference. This change in the SST causes a latitudinal shift in the ascending branch of the Hadley cell and precipitation in the tropics, as well as an increase in the atmospheric meridional heat transport from the warmer to the colder hemisphere.

Submitted by Lucienne Costa (lucienneferreira@ufcg.edu.br) on 2018-08-13T19:06:36Z No. of bitstreams: 1 LADY LAYANA MARTINS CUSTÓDIO – DISSERTAÇÃO (PPGMET) 2017.pdf: 2210710 bytes, checksum: 55d1c243d2dffba97fddd5fcb1e2b54b (MD5) / Made available in DSpace on 2018-08-13T19:06:36Z (GMT). No. of bitstreams: 1 LADY LAYANA MARTINS CUSTÓDIO – DISSERTAÇÃO (PPGMET) 2017.pdf: 2210710 bytes, checksum: 55d1c243d2dffba97fddd5fcb1e2b54b (MD5) Previous issue date: 2017-03-03 / Capes / Buscou-se avaliar neste trabalho as precipitações da EC e da PEC do LNEB e Roraima, bem como a relação entre esta variável nas duas áreas de estudo objetivando entender melhor os sistemas precipitantes que causam a EC, que, em geral, ocorre no trimestre abril, maio e junho, portanto, fora do período de monções na AS. Bem como verificar a relação da precipitação do LNEB e Roraima com a TSM do Pacífico Equatorial e Atlântico Tropical. Para tanto, utilizou-se de dados diários de precipitação de 1979 a 2013, provenientes do CFSR do NCEP, além dos dados do projeto Era-Interim do ECMWF de mesmo período e por fim, dados mensais oceânicos das regiões do El Niño e dos setores do Atlântico no período de 1982 a 2013. A princípio, calculou-se os ciclos pêntadais da precipitação, no qual, analisou-se as séries temporais das áreas de estudo e padrões atmosféricos associados. Usou-se o método hierárquico aglomerativo de Ward para classificar as regiões homogêneas de precipitação de ambas as áreas de estudo. A relação entre a TSM e a precipitação do LNEB e em Roraima e entre as precipitações destas áreas foi estimada pelo coeficiente de correlação de Pearson. Os resultados obtidos mostraram três grupos homogêneos de precipitação em Roraima e dois no LNEB. Em média a EC para as áreas de estudo tem início na pêntada 17 e final na pêntada 40. A PEC para LNEB e Roraima mostrou-se inconsistentes, pois dos cinco grupos de precipitação, em quatro, o número de ocorrências de PEC foram abaixo da metade da série histórica. As altas pressões ao nível do mar dos setores do Atlântico exercem função fundamental na contribuição da EC do LNEB e Roraima. Também se verificou que o ENOS tem papel relevante nas variabilidades interanuais da precipitação do LNEB e de Roraima, tanto nos totais anuais como nos da EC. As chuvas em Roraima apresentam correlação estatisticamente significativa com a TSM do norte do Atlântico, e as da região do Agreste do LNEB com a TSM do Atlântico Sul. Observou-se que as variabilidades interanuais dos totais anuais e sazonais de precipitação de Roraima e LNEB estão em fase, ou seja, em geral, os anos chuvosos em Roraima são os mesmos do LNEB, assim como os secos. As conclusões mais relevantes foram: a EC em Roraima possui regime tipo monções de surgimento brusco e término lento, enquanto a do LNEB apresenta transição gradual, configurando um regime diferente dos de monções; os sistemas meteorológicos produtores de precipitação nas duas regiões são diferentes, porém atuam na mesma época do ano; a marcha anual dos totais pentadais de precipitação ao longo do ano são as mesmas e são influenciados pelo ENOS e pela intensidade e posição das altas pressões do Atlântico resultando em variabilidades interanuais da precipitação em fase nas duas regiões. / The aim of this study was to evaluate the precipitations of the RS and PRS of the ENEB and Roraima, in addition to the relation between this variable in the two study areas for the sake of getting a better understanding of the precipitating systems that cause RS, which generally occurs in the quarter of April, May and June, thus outside the monsoon period in SA. Additionally the study aimed to verify the relation of the precipitation of the ENEB and Roraima with the SST of the Equatorial Pacific and Tropical Atlantic. In order to do so, daily precipitation data from 1979 to 2013 from the NCEP CFSR were used, apart from Era-Interim data from the ECMWF project of the same period and, finally, monthly ocean data from the El Niño regions and the Atlantic sectors from 1982 to 2013. At first, the 5-days cycles of the precipitation were calculated, in which the time series of study areas and the atmospheric patterns associated were analyzed. Ward's agglomerative hierarchical clustering method was used to classify the homogeneous precipitation regions of both study areas. The link between the SST and precipitation in ENEB and Roraima and between precipitations in these areas was estimated by the Pearson correlation coefficient. The results obtained showed three homogeneous groups of precipitation in Roraima and two in the ENEB. On average, the RS for the study areas starts at the 17 pentad and at the end at the 40 pentad. The PRS for ENEB and Roraima appeared to inconsistent, because among the five precipitation groups, four of them presented a number of PRS occurrences below half of the historical series. The high sea-level pressure of the Atlantic sectors play a fundamental role contributing to the ENEB and Roraima RS. It was also verified that the ENSO has a relevant role in the interannual variability of the ENEB and Roraima precipitation, both in the annual totals and in the RS. The rainfall in Roraima shows a statistically significant correlation with the SST of the North Atlantic, and those of the Agreste region of the ENEB with the SST of the South Atlantic. We observed that the interannual variabilities of the annual and seasonal precipitation totals of Roraima and ENEB are in-phase, that is, in general, the rainy years in Roraima are the same as in the ENEB, in addition to the dry ones. The most relevant conclusions were: the RS in Roraima has a monsoon type regime with abrupt onset and slow ending, while the ENEB has a gradual transition, forming a regime different from that of the monsoons; the meteorological systems producing precipitation in the two regions are different, however acting at the same time of year; the annual marching of the pentad totals of precipitation throughout the year are the same and are influenced by the ENSO and the intensity and position of the high pressure of the Atlantic, resulting in interannual variabilities of the precipitation in phase in the two regions.