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

This paper describes the physical processes associated with the occurrence of a heat wave over central Argentina during the austral summer of 2002-2003, during which the South American Low-Level Jet Experiment (SALLJEX) was carried out. GDAS analyses, observations from the national weather services and the valuable set of observations collected by SALLJEX during that particular summer were used. The SALLJEX heat wave that lasted between 25 January and 2 February of 2003 was punctuated by extreme conditions during the last 3 days with the largest historical temperature recorded over the last 35 years in 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 that particular 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. Temperature 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 begun to dominate over central Argentina due to the intensification of the South American Low-Level Jet. The approach of an extratropical frontal system produced the maximization of such mechanisms leading to temperature extremes by 2 February with temperature anomalies at least two standard deviations larger than the climatological mean values. It can be then concluded that adiabatic subsidence and diabatic warming associated with the SACZ activity, followed by the horizontal advection associated with the southward intensification of the SALLJ were the leading mechanisms promoting the development of the SALLJEX heat wave in subtropical South America. Future works are planned in order to assess whether the mechanisms discussed here are a more common characteristic of the tropical-extratropical interactions over South America, which it would certainly contribute to increase the predictability levels in the region beyond the synoptic timescales..Pages: 981-98