The nature of a heat wave in eastern Argentina occuring during SALLJEX

Abstract

This note describes the physical processes associated with the occurrence of a heat wave over central Argentina during the austral summer of 2002/03, during which the South American Low-Level Jet Experiment (SALLJEX) was carried out. The SALLJEX heat wave that lasted between 25 January and 2 February 2003 was punctuated by extreme conditions during its last 3 days, with the highest temperature recorded over the last 35 yr at several stations of the region. It was found that not only the activity of synoptic-scale waves, but also the intraseasonal oscillation variability, had a strong impact on the temperature evolution during this summer. During the weeks previous to the heat wave development, an intensified South Atlantic convergence zone (SACZ) dominated the atmospheric conditions over tropical South America. Temperatures started to increase in the subtropics due to the subsidence and diabatic warming associated with the SACZ, as depicted by SALLJEX upper-air observations. An extratropical anticyclone that evolved along southern South America further intensified subsidence conditions. By the end of January the warming processes associated with SACZ activity weakened, while horizontal temperature advection began to dominate over central Argentina due to the intensification of the South American low-level jet. This mechanism led to temperature extremes by 2 February with temperature anomalies at least two standard deviations larger than the climatological mean values. Intense solar heating favored by strong subsidence was responsible for the heat wave until 31 January, after which horizontal temperature advection was the primary process associated with the temperature peak.