Variability in the South Atlantic anticyclone and the Atlantic Niño mode

Abstract

Previous studies have argued that the strength of the SouthAtlantic subtropical high pressure system, referred to as the South Atlantic anticyclone (SAA), modulates sea surface temperature (SST) anomalies in the eastern equatorial Atlantic. Using ocean and atmosphere reanalysis products, it is shown here that the strength of the SAA from February toMay impacts the timing of the cold tongue onset and the intensity of its development in the eastern equatorialAtlantic via anomalous tropical wind power. Thismodulation in the timing and amplitude of seasonal cold tongue developmentmanifests itself via SST anomalies peaking between June andAugust. The timing and impact of this connection is not completely symmetric for warm and cold events. For cold events, an anomalously strong SAAin February andMarch leads to positive wind power anomalies fromFebruary to June resulting in an early cold tongue onset and subsequent cold SST anomalies in June and July. For warm events, the anomalouslyweakSAApersists untilMay, generating negativewind panomalies that lead to a late cold tongue onset as well as a suppression of the cold tongue development and associated warm SST anomalies. Mechanisms by which SAA-induced wind power variations south of the equator influence eastern equatorial Atlantic SST are discussed, including ocean adjustment via Rossby and Kelvin wave propagation, meridional advection, and local intraseasonal wind variations.