Características dos Sistemas Convectivos de Mesoescala que geraram granizo e atingiram o Rio Grande do Sul entre 2004 e 2008

Abstract

The state of Rio Grande do Sul (RS), due to its subtropical location, is under the influence of various meteorological phenomena capable of generating severe weather condition (SW). Among these phenomena, highlight the Mesoescale Convective Systems (MCS), defined as convective cloud clusters. The MCS are responsible for the most SW in RS, which hail the most destructive, since the state’s economy is focused on agribusiness and this type of SW directly impacts the agricultural sector. Therefore, this study aimed to analyze the characteristics of the 34 MCS that affected RS and caused hail (MCSHAIL) between 2004 and 2008, from total and seasonal distribution of MCSHAIL, differentiated according to their origin: continental or oceanic, diurnal or nocturnal and frontal or non-frontal. For the selection of MCSHAIL was utilized the ForTrACC (Forecasting and Tracking Active Cloud Clusters) application, the rough images of the GOES (Geostationary Operational Environmental Satellite) 10 and 12 satellite of the channel 4 (thermal infrared) with space resolution in the subsatellite point of 4 km x 4 km and the timeresolution of 30 minutes, and records of SW and municipalities affected obtained from the database of the State Civil Defense Coordination of RS (DCRS) of the period of 1/1/2004 to 12/31/2008. The results showed that the MSCHAIL were more numerous in the quarter from July to September. With respect to the origin of the systems, 91% of MSCHAIL had genesis on the continent, 56% were classified as diurnal, and 71% were associated with the passage of frontal systems. In general, the MCSHAIL formed between the western RS, northeastern Argentina, southern Paraguay and northwestern Uruguay, and showed preferential displacement to eastward, similar to the large-scale circulation at mid-latitudes. Among the most frequent MCSHAIL (continental, diurnal and frontal – MCSHAIL-CDF) the formation occurred mainly between the western RS and the northeastern of Argentina, with displacement to eastward. The MCSHAIL-CDF generated losses in agriculture in one third of RS cities affected.