A principal fonte de energia do planeta Terra é o Sol. A energia que chega aquece primeiramente a superfície terrestre e depois, por intermédio de alguns processos físicos entre a superfície e a atmosfera, o ar adjacente também é aquecido. Entretanto, o aquecimento da Terra não ocorre de maneira uniforme entre polos e equador. Devido à forma da Terra, os raios solares atingem a região tropical IntroduçãoA América do Sul (AS) possui grande extensão latitudinal, ocupando desde áreas equatoriais até de latitudes médias; portanto, diferentes regimes climáticos são encontrados no continente.Assim, o objetivo deste trabalho é apresentar os conhecimentos meteorológicos básicos para o entendimento do tempo e clima vigentes no continente sul-americano. ABSTRACT Underrstanding Weather and Climate in South America: South America (SA) has a diversified geography that enables the development and action of different atmospheric systems. These systems contribute to the spatial and temporal non-homogeneity of precipitation patterns. This study has as purposes: (a) to provide basic concepts from weather and climate, (b) to present the precipitation climatology and (c) to describe the atmospheric systems that contribute to the diverse annual cycles of precipitation in each region

A B S T R A C TThe region under study is regularly subject to the occurrence of storms associated with frontal systems and extratropical cyclones, since it is located near one of the cyclogenetic regions in South America. These storms can generate storm surges that cause anomalous high sea level rises on Cassino Beach. The use of reanalysis data along with an efficient technique for the location of the cyclone, using a vorticity threshold, has provided a new classification based upon the trajectories of events that produce positive sea level variation. Three patterns have been identified: 1) Cyclogenesis to the south of Argentina with displacement to the east and a trajectory between 47.5ºS and 57.5ºS; 2) Cyclogenesis to the south of Uruguay with displacement to the east and a trajectory between 35ºS and 42.5ºS; and 3) Cyclogenesis to the south of Uruguay with displacement to the southeast and a trajectory between 35ºS and 57.5ºS. Maximum water level elevation above the mean sea level and beach erosion were associated, respectively, with winter and summer storms. Cassino beach displayed a seasonal morphological behavior, with short periods of episodic erosion associated with winter storm events followed by long periods of accretion characterized by the dominance of fair weather conditions. R E S U M OMarés meteorológicas que geram sobre-elevações do nível do mar são freqüentes na costa do Rio Grande do Sul e respondem às variações ocorridas na atmosfera. Torna-se importante, dessa maneira, definir padrões meteorológicos sinóticos responsáveis por gerar eventos de marés meteorológicas intensas na Praia do Cassino como objetivo desse trabalho. O uso de dados de reanálise associados a uma técnica eficiente de localização do ciclone, aplicando o conceito de vorticidade, permitiu definir uma nova classificação com base na trajetória de ciclones extratropicais responsáveis pela subida do nível do mar. Três padrões de trajetórias foram identificados: 1) Ciclogênese ao sul da Argentina com deslocamento para leste e trajetória entre 47.5ºS e 57.5ºS; 2) Ciclogênese ao sul do Uruguai com deslocamento para leste e trajetória entre 35ºS e 42.5ºS; 3) Ciclogênese ao sul do Uruguai com deslocamento para sudeste e trajetória entre 35ºS e 57.5ºS. O estudo de 23 ciclones extratropicais permitiu verificar máximas elevações do nível e erosão respectivamente associados a tempestades ocorridas no inverno e verão. A Praia do Cassino apresentou um comportamento sazonal, com erosão episódica associada a eventos de alta energia mais freqüentes no inverno, e longos períodos de acresção relacionados ao regime hidrodinâmico normal.

The impacts of change in the Grell convective scheme and biosphere−atmosphere transfer scheme (BATS) in RegCM3 are described. Three numerical experiments (RegZhang, RegClaris and RegArain) are conducted to reduce the RegCM3-Grell rainfall underestimation over tropical South America. The simulation referred to as RegZhang follows modifications made by Zhang et al. (2008) in the BATS. The RegClaris combines the RegZhang BATS parameters with a reduction of water drainage at the bottom of the subsoil layer in the regions covered by the tropical rain forest and a shorter convective time period for the Grell scheme. The RegArain considers this same modification in the Grell scheme, but uses a deeper total soil column and a deeper root system in the BATS. After the first year of simulation, the soil water content in RegZhang is progressively drained out of the soil column resulting in a deficit of rainfall in the Amazon. The RegClaris and RegArain, on the other hand, simulate a similar rainfall annual cycle in the Amazon, showing substantial improvement not only in phase but also in intensity. This improvement is partially related to an increase in evapotranspiration due to a larger availability of water in the soil column. A remote effect is also noted over the La Plata Basin region, where the larger summer rainfall rate may be related to the increase in moisture transport from the Amazon. Wind-and rainfall-based indices are applied to identify South American monsoon (SAM) timing. The RegClaris rainfall rates are adequate to identify the onset and the demise of SAM according to the observed data, whereas the rainfall deficit in RegZhang is associated with a delay in the onset and an early demise of the SAM.

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