A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

CONTINENTAL SQUALL LINE FORMATION OVER EASTERN AMAZÔNIA.Julia Clarinda Paiva Cohen (1) , Adilson Wagner Gandu (2) , José Ricardo S. de Souza (1)(1) Department of MeteorologyFederal University of Pará, Belém, Brazile-mail : jcpcohen@ufpa.br(2) Departament of Atmospheric SciencesUniversity of São Paulo, São Paulo, Brazile-mail : adwgandu@model.iag.usp.brABSTRACTThis paper presents the observational results of two squall lines (SL) originated overthe continental eastern part of the Amazon Region.Satellite images and automatic weather stations observations at three sites(Bragança, Soure and Caxiuanã), located along a 500 km transect parallel to the equatorand between 0 and 2 degrees south, were used to monitor the SL´s genesis anddisplacement.The observation period, between 17 and 18 September, 2002, was within the drierseason. Nevertheless the pluviommetric precipitation monitored at three experimental sites,indicated the occurrence of a large scale convective system over the region. Thisatmospheric system produced a nearly 4 o C temperature fall below seasonal daily average inSoure and Bragança. This fact might be associated to downdrafts during the local dayligthhours. Precipitation intensities in Soure and Caxiuanã reached 36 mm/h , followed by 8mm/h observed in Bragança.It was observed from the satellite images that before the disturbance, there weresome scattered convective clouds, over the central portion of the state of Maranhão. Thecombination of an easterly wave disturbance plus the existence of a 300 m high topographyto the west appear to have produced an internal gravity wave, which apparently organizedthose clouds in a linear form. The propagation speed of the SL´s formed was about 14 m/s.Even though these continental SL´s have different generation mechanisms from themaritime breeze circulation, which produce SL´s along the Atlantic coast of Amazonia(Kousky, 1980 ; Cohen et al, 1995); the present case study shows that they both havesimilar structure and propagation speeds.Corresponding author address : Dr. Julia Clarinda Paiva Cohen.Departamento de Meteorologia - Centro de Geociências- UFPACP. 1611 , Belém Pará Brasil CEP 66075-900.