Influence of the intraseasonal variability on heat waves in subtropical South America

CERNE, S. BIBIANA; VERA, CAROLINA

CLIMATE DYNAMICS

SPRINGER

Lugar: Berlin, Alemania; Año: 2010

0930-7575

The influence of the intraseasonal variability onheat wave development over subtropical South Americaduring austral summer is analyzed. The role of the SouthAtlantic Convergence Zone (SACZ) on this development isdocumented. Results show that intraseasonal variabilitycan explain on average at least 32% of summer temperaturevariance. Moreover, 73% of the heat waves in subtropicalSouth America develop in association with an activeSACZ. The analysis of pentad maps shows that warmconditions in the region under study develop in associationwith the strengthening of an anticyclonic anomaly, which isdiscernible over the subtropical regions at least 15 daysbefore temperature peak occurrence. That circulationanomaly is embedded in a large-scale Rossby wave trainextending along the South Pacific Ocean that is linked toconvection anomalies at the equatorial western and centralPacific Ocean. In addition, the development of the anticycloniccirculation over subtropical South America appearsto be strengthened by the subsidence conditions promotedby the active SACZ, which result in temperature rise in thesubtropical region under relatively dry conditions. On theother hand, during the last 2 days of evolution, SACZactivity weakens and the progressive temperature rise inthe region is dominated by warmer and moister air beinganomalously advected from the north. Results confirm theimportant role that SACZ activity on intraseasonal timescales has in inducing persistent circulation anomalies atthe subtropical regions that can result in the developmentof persistent heat waves, and very extreme dailytemperature.