Um estudo da relação entre precipitação, evaporação e adecção de umidade no Nordeste brasileiro.

Abstract

In this work some statistical and numerical studies were made toward a better understanding of the relationship between surface wind, through its induction of evaporation as well as through its role as a moisture advection mechanism, upon the precipitation regime of the region Northeast of Brazil (NEB). In this study, harmonic analysis of monthly data of rainfall and near-surface wind were performed in order to understand the climatic character of this relationship. In addition, numerical experiments using the model RAMS were run for a view of the short-range effects. For the harmonic analysis, monthly means of 724 rainfall stations and 77 wind stations were used. Results suggest that the annual cycles of both the wind and the precipitation are very strong over most of the NEB. Furthermore, there is a lag of about six months between the maxima of wind and precipitation. The numerical experiments for a 48 h run suggest that for dry years, like 1983, rainfall increases with increase of the soil moisture available for evaporation. On the other hand, for a wet year like 1986, rainfall decreases with increase of the soil moisture available for evaporation. This is due to the fact that during wet years the main source of moisture for precipitation comes from the ocean through advection. In general, the nonlinear interaction between local evaporation and advection as a precipitation producing mechanism is negative since the moisture evaporated at a place is advected away. Although topography has not been tested as a separate factor, the results suggest that its effect as a forcing mechanism is important to precipitation over elevated terrain.