Distúrbios de leste: diagnóstico e relação com a precipitação no Estado da Paraíba em períodos de contraste.

Abstract

This study analyzes June 1995, 1996, 1997 and 1999, contrasting months in terms of the SST anomaly fields, with the objective of: (a) to identify easterly disturbances that reached Northeast Brazil, (b) to characterize their dynamical and thermodynamical structures and (c) to evaluate their contribution to the rainfall totals in Parafba State. The analyses were based on daily rainfall totals collected by the raingauge network of Parafba State, Meteosat satellite images, sea surface temperature anomalies, and meteorological data from NCEP reanalyses. Results show that: (a) the disturbances have mean period of 5 days and mean propagation speed of 9° of longitude per day; (b) the number of disturbances is significantly smaller in June 1997 (a dry month in eastern Parafba State), a month with strong positive SST anomalies in the Equatorial Pacific and negative SST anomalies in the Atlantic; (c) low-level moisture convergence associated with the mean flow (trade winds) seems to explain the above normal rainfall totals in June 1995, a month with SST anomalies similar to the anomalies of June 1996 in the Pacific (neutral) and Atlantic (small positive); (d) the disturbances change the thermodynamic structure of the atmosphere by causing, in general, an increase in the atmospheric moisture content and in the thickness of the convectively unstable layer, whose magnitudes depend on the ambient conditions at the time of the disturbances' arrival.