Identificação das ondas de calor na região subtropical do Brasil: características observacionais e simuladas através do modelo DREAM

Abstract

Heat waves are extreme events that leads to several impacts and socioeconomic damages during its performing. Considering that heat waves are becoming more frequent and intense as a result of global warming, it is very important to improve the knowledge about the atmospheric mechanisms involved in their development. Thus, the main objective of this research is to identify heat wave events in two domains in the subtropical region of Brazil from 1980 to 2016 and define the main dynamic and thermodynamic mechanisms associated with this phenomenon. The events were selected through monthly percentiles from statistical data analysis and applied to daily Tmax anomalies from Xavier, King e Scanlon (2015) and CPC dataset. To characterize the behavior of the atmosphere during the heat waves, in the climatological analysis and in the study cases, climatological composites and lag-composites were used with MSLP, GHT, specific humidity, horizontal wind, vertical velocity (from ERA-5 reanalysis) and OLR (NOAA) data. This analysis was performed by region and for each month of the year, to evaluate possible differences in atmospheric patterns depending on the region and month of action of the heat wave. Through the meteorological fields analysis, the development of a wave train between the Pacific and the South Atlantic Ocean was observed, which favored the establishment of a persistent anticyclonic center close to the heat wave region. This atmospheric composition favored subsidence over the affected area, which leads to heating by compression of the air (adiabatic) and by the increase in the solar radiation (diabatic). Furthermore, low-level anticyclonic circulation tends to favor advection of warm air from lower latitudes towards the subtropics. At high levels, the jet stream was positioned at higher latitudes, sothern of the affected area, blocking the cold fronts and maintaining the persistence of extreme temperatures. Finally, a heat wave simulation was performed using the dynamic model IGCM DREAM. Despite presenting differences in the magnitude of the anomalies, the model provided a satisfactory representation of the phenomenon.