Atmospheric characteristics favorable for the development of mesoscale convective complexes in southern Brazil

Abstract

Mesoscale convective complexes (MCCs) are meteorological events that result in severe storms, hail, flood, and tornadoes, but they are difficult to forecast. In South America (SA), MCCs are usually larger and last longer than those in the USA. Southern Brazil (SB) is one of their preferred regions of occurrence. This study’s objective was to contribute to the identification of the main physical characteristics and atmospheric environment that favors the occurrence of MCCs in SB and determine how these events are unique relative to other subtropical SA (OSSA) regions. Results indicate that SB MCCs last longer (+3 h) and their average maximum extent is at least 50000 km2 larger than OSSA MCCs. The atmospheric environment of SB MCCs meets the criteria already indicated in previous studies, with the northerly low-level jet (LLJ), which brings humidity from the Amazon Basin to the SB MCCs genesis area, coupling with the upper-level jet (ULJ). Moreover, SB MCCs have the South Atlantic as their second source of moisture, which is advected by anticyclonic circulation in the southwestern South Atlantic. This indicates that SB MCCs have unique characteristics compared to OSSA MCCs, including 2 main atmospheric circulation systems responsible for moisture advection to the SB genesis region. For comparison, OSSA MCCs are more dependent on the South Atlantic Convergence Zone (SACZ) and the advection of moisture by the LLJ from the Amazon Basin to north-central Argentina and west-central and southeast Brazil.