Mechanisms Associated with Large Daily Rainfall Events in Northeast Brazil


Brant Liebmann
CIRES Climate Diagnostics Center, Boulder, Colorado

George N. Kiladis
Physical Sciences Division, NOAA/Earth System Research Laboratory, Boulder, Colorado

Dave Allured
CIRES Climate Diagnostics Center, Boulder, Colorado

Carolina S. Vera
Department of Atmospheric and Ocean Sciences, CIMA/UBA-CONOCET, Buenos Aires, Argentina

Charles Jones
Institute for Computational Earth System Science, University of California, Santa Barbara, Santa Barbara, California

Leila M.V. Carvalho
Department of Atmospheric Sciences, Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo, São Paulo, Brazil

Ileana Bladé
Departament d'Astronomia i Meteorologia, Facultat de Física, Universitat de Barcelona, Barcelona, Spain

Paula L. M. Gonzáles
Department of Atmospheric and Ocean Sciences, CIMA/UBA-CONOCET, Buenos Aires, Argentina

(Manuscript received 1 October 2009, in final form 3 August 2010)

Abstract

The mechanisms resulting in large daily rainfall events in Northeast Brazil are analyzed using data filtering to exclude periods longer than 30 days. Composites of circulation fields that include all independent events do not reveal any obvious forcing mechanisms as multiple patterns contribute to Northeast Brazil precipitation variability. To isolate coherent patterns, subsets of events are selected based on anomalies that precede the Northeast Brazil precipitation events at different locations. The results indicate that at 10°S, 40°W, the area of lowest annual rainfall in Brazil, precipitation occurs mainly in association with trailing midlatitude synoptic wave trains originating in either hemisphere. Closer to the equator at 5°S, 37.5°W, an additional convection precursor is found to the west, with a spatial structure consistent with that of a Kelvin wave. Although these two sites are located within only several hundred kilometers of each other and the midlatitude patterns that induce precipitation appear to be quite similar, the dates on which large precipitation anomalies occur at each location are almost entirely independent, pointing to separate forcing mechanisms.