Convection and precipitation in the Southern Amazon region: Comparison between a normal and dry year

We examine the diurnal cycles of deep convection and precipitation in the Southern Amazon region, using mainly the Advanced Microwave Sounding Unit, contrasting a year of drought (2004-2005) with a “normal” year (2005-2006). MODIS 550nm aerosol optical thickness data and TRMM 3B42 precipitation products were also used to investigate whether a significant relationship between these two parameters can be identified. We use a simple, tractable method to identify convective areas based on humidity channels of AMSU. We found through comparisons with independent ground precipitation data that the diurnal cycle of convection in regional scale can be realistically described by this method. We observe that deep convective areas have a slow build-up early in the rainy season of the dry year, and rapid in the normal year, and in both cases, convection starts around midday. As the rainy season advances, the peak hour of maximum convective activity shifts towards mid-afternoon, and eventually spreads towards the night. During the peak of rainy season (December through February) convective activity was up to 12% larger in the “normal” year. Convective overshooting was found to be 50% less frequent in the drought year compared to the following year. A simple spatial correlation analysis of MODIS 550nm and TRMM 3B42 monthly mean data showed that by the end of dry season, aerosol loading and precipitation amounts have a positive (albeit low) significant correlation.