Interannual variability of deep convection over the tropical South American sector as deduced from ISCCP C2 data

Abstract

AbstractThe interannual variability of deep convection over the South American sector and regional hydrometeorological anomalies are studied using International Satellite Cloud Climatology Project (ISCCP) data for 1984–1988. Satellite‐derived convection anomalies are compared with regional rainfall and river runoff anomalies.At the height of the austral summer, the deep convective clouds (DCC) and ISCCP depict the centres of intense convection over central Amazonia and the mouth of the River Amazon, as well as the enhanced convection over north‐east Brazil, which is related to the Atlantic Intertropical Convergence Zone (ITCZ). Positive/negative regional hydrometeorological anomalies are consistent with positive/negative anomalies in the deep convection over northern Amazonia, the mouth of the River Amazon and north north‐east Brazil, whereas this is not always true over southern Amazonia and southern Brazil. Over north‐east Brazil and the mouth of the River Amazon, abundant rainfall and large DCC are both in agreement with variations in the latitudinal position and intensity of the Atlantic ITCZ, which extends between 4°N and 5°S along the Atlantic coast, where the precipitation maximum is found. The related rainfall anomalies over Amazonia and north‐east Brazil during years with anomalously warm or cool surface waters in the central equatorial Pacific (e.g. the El Niño event in 1987), are consistent with the convection anomalies as depicted by the ISCCP deep convective clouds. For the Amazon Basin and north‐east Brazil, DCC based on 2.5°×2.5° horizontal resolution explained about 50 per cent of the variance of rainfall at individual surface stations.A new finding is the enhanced convective activity located at the east side of the central Andes and over central Amazonia around 5°S, with a region of reduced convection in between. These two subcentres are oriented west‐east and are part of the summertime semi‐permanent centre of convection over the Amazon Basin, and have not been identified previously from the analysis of outgoing longwave radiation (OLR) or highly reflective clouds. These subcentres of large DCC exhibit interannual variations in intensity and location, where the centre located near the east flank of the Andes shows a wider range of latitudinal variations than that located over central Amazonia. South of this area convection and rainfall decreases rapidly.