The Intertropical Convergence Zone in the South Atlantic and the Equatorial Cold Tongue

Abstract

Recent observations from the QuikSCAT and Tropical Rainfall Measuring Mission satellites, as well as a longer record of Special Sensor Microwave Imager winds are used to investigate the existence and dynamics of a Southern Hemisphere partner to the intertropical convergence zone in the tropical Atlantic Ocean. The southern intertropical convergence zone extends eastward from the coast of Brazil in the latitude band 10°?3°S and is associated with seasonal precipitation exceeding 6 cm month?1 during peak months over a part of the ocean characterized by high surface salinity. It appears in austral winter when cool equatorial upwelling causes an anomalous northeastward pressure gradient to develop in the planetary boundary layer close to the equator. The result is a zonal band of surface wind convergence that exceeds 10?6 s?1, with rainfall stronger than 2 mm day?1, and an associated decrease in ocean surface salinity of 0.2 parts per thousand.