The climatology and variability of the South Atlantic Convergence Zone

The climatology of South America shows a prominent cloudiness feature, the South Atlantic Convergence Zone (SACZ), extending from the Amazon basin towards southeast Brazil and the western portion of the subtropical Atlantic Ocean. Previous studies have shown that the SACZ plays a dominant role in the summertime precipitation variability. The SACZ is also characterized by significant temporal variability from intraseasonal-to-interannual time scales. This study provides a new way to objectively characterize some fundamental structural properties of the SACZ and its temporal variability, intensity, geographical location and persistence. Daily Outgoing Longwave Radiation (OLR) and precipitation data derived from the Special Sensor Microwave Imager (SSM/I) from the period January 1979-1999 are used. A computer algorithm uses OLR thresholds to identify periods of SACZ activity. The method further identifies some structural properties of the SACZ, such as geographic center (i.e. center of gravity), area, perimeter, axis of orientation and temporal persistence. The presentation will discuss the mean climatological features of the SACZ as well as frequency distribution of structural properties, persistence and seasonal variability.