Synoptic Aspects of a Polar Outbreak Leading to Frost in Tropical Brazil, July 1972

Abstract

An outbreak of cold air of polar origin which brought frost to Brazil near 23°S and caused substantial damage to coffee plantations during the second week of July 1972 was investigated using radiosonde, radiowind, surface meteorological and satellite data. These data were combined to provide details of the three-dimensional structure and life cycle of synoptic features associated with the outbreak. Widespread frost occurred in the coffee plantations between 400 and 800 m altitude in Paraná and neighborhood beneath clear skies within a dry, convectively stable westerly current eastward of the center of a cold-cored anticyclone which developed below 700 mb within an airstream that had followed a long overland track from southern Argentina. Rapid equatorward advection of this cold air beyond 25°S occurred between the anticyclone, which was developing over northern Argentina, and a depression that was moving southeast across the coast of Brazil near 30°S close to the boundary of the cold airstream, which had just moved northeast into Uruguay. Over central Brazil, the surface cold front advanced to 10°S, causing maximum and minimum temperatures to fall by 10?15°C over a very wide area.