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

Dynamic and Synoptic Features of a Cold Outbreak during Wet-Season on SouthwesternAmazonMarcos LongoMaria Assunção Faus da Silva DiasRicardo de CamargoInstituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São PauloRua do Matão 1226, Cidade Universitária, 05508-900, São Paulo, SPTel.: +55 +11 3091 4808 FAX: +55 +11 3091 4808E-mail: marcos@master.iag.usp.brThe aim of this work is to analyse a cold outbreak, or “friagem”, event that reachedSouth-western Amazon and Southern and Middle Brazil on November 9 th , 1999. Usingsatellite images, CPTEC-INPE analysis and surface and sounding data, it was found that thisevent induced, on South-western Amazon Basin, decrease of temperature — reaching about12°C — and specific humidity — as low as 8 g/kg — and increase of wind magnitude — to 7m/s southerlies. Convection activity, which was intensified before cold front interaction, wassuppressed for 2-3 days after the cold outbreak.Since vorticity advection at middle to high troposphere is related to temperatureadvection at low levels, it was verified that the anticyclonic advection induces pressureincrease at west side of trough and pressure decrease at east side of trough. This feature inpressure field generates cold advection in low levels, which intensifies the trough.Cold advection was the most important term in the temperature budget equation, andan equilibrium was found between adiabatic cooling and diabatic heating. While it movednorthward, the layer which has cold advection became shallower.