Estudo sinotico de periodos deficientes de chuvas no Rio Grande do Sul / Synoptic study on periods of deficiency over Rio Grande do Sul/Brazil

AUTOR(ES)
DATA DE PUBLICAÇÃO

1992

RESUMO

The rainfall regime in the State of Rio Grande do Sul (Brazil) is characterized by a homogeneous monthly distribution and a low interannual variability. A spacial series considering 39 years of precipitation data (1952-1990) was used to analyse the years which had periods of rain deficiency. In the years 1988 and 1989 the annual precipitation presented meaningful negative deviation. Two summer seasons (January and February) which presented negative anomalous behavior during these years were selected. A synoptical study, using geopotential fields, vertical velocity, relative vorticity, vorticity advection, and divergence fields was performed to analyse this period of rain deficiency. The South Atlantic Convergence Zone (SACZ) was observed to persist during the February months which registered a significant negative deviation precipitation. Related to the SACZ, the presence of a trough was noticed over to the east of Rio Grande do Sul state. At the same time, a trough in the Pacific Ocean was found about 120° W. This atmospheric pattern showed to be stationary in February, suggesting effects similar to a blocking situation. As a result, the frontal systems were deviated from their usual path over the State of Rio Grande do Sul. The position of the trough axis, to the east of Rio Grande do Sul induced a persistent subsidence which contributed to inhibiting the convective activity over the region. This period with anomalous negative precipitation coincided with the presence of a positive Southern oscillation Index in the Pacific Ocean.

ASSUNTO(S)

rain meteorologia sinotica chuva meteorology

ACESSO AO ARTIGO

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