Concomitant heat waves in Central Chile and Southeastern South America: Synoptic Enviroment, Impacts and predictability

MARTIN JACQUES COPER; ANNA SÖRENSSON; CAMILA DESIREE ALVAREZ-GARRETON; LLUÍS FITA BORELL; DANIEL VELOSO-ÁGUILA; PABLO G. ZANINELLI; MARIANO ALVAREZ; ALVARO GONZALEZ-REYES

San Francisco

Congreso; AGU FALL MEETING; 2019

Heat waves have drawn major attention in southern South America due to their related socio-economic impacts, such as health emergencies, energy and water supply shortages, and wildfires, among others. Therefore, the understanding of the factors leading to these extreme events, along with any additional information on their predictability -beyond typical weather forecasting-, are of paramount relevance for operational purposes.In this study, we explore heat waves developing, with a time lag of a few days, in both Central Chile (30º-40ºS) and Southeastern South America (SESA, encompassing the La Plata Basin), which house each country's population majority. In particular, we focus on the intra-seasonal variability extracted from instrumental temperature records from Santiago (Chile) and Buenos Aires (BA, Argentina) starting in the 1960s. The NCEP-NCAR and 20th Century Reanalyses support our research.Common events comprise, for example, the prominent February 1965 (38ºC maximum temperature (Tmax) in BA, highest measured value for that month) and the January 2003 heatwaves. Beyond the instrumental record, we also identify the all-time record-breaking January 1957 heatwave (45ºC Tmax in BA) and, in a broader region, the extremely hot conditions at both sides of the Andes Cordillera in January 1934 (36ºC Tmax in Curicó, Chile, and 44.8ºC in Santa Fe, Argentina).We confirm that a coastal low in Chile followed by an mid-latitude cyclone in SESA are instrumental for the regional temperature rises. The associated warm anomalies increase the height of the freezing level over the Andes Cordillera, which might impact the regional cryosphere. Besides, we find guidance for an improved forecast stemming from extra-tropical (Antarctic Oscillation) and tropical (Madden-Julian Oscillation) sources. Planned future numerical studies will allow the exploration of the modulating roles played by land use (e.g. forest plantations versus native forests) and surface humidity in selected cases.