Decadal Variability of Southern Subtropical SST Wavenumber-4 Pattern and Its Impact

Abstract

A decadal variability is revealed in sea surface temperature (SST) wavenumber-4 (W4) pattern of southern subtropics (20°–55°S) using wavelet and empirical orthogonal function analysis. The decadal variability of the SST W4 pattern evolves from the decadal modulation of the South Pacific Meridional Mode (SPMM) as seen in SST footprints. The SST residuals of the SPMM create a favorable environment for the frequent occurrence of positive/negative type of the SST W4 pattern and is discussed. Since SST W4 pattern covers the globe, it potentially affects the decadal rainfall variability over Southern continents by modulating local atmospheric circulation. During positive phase, anomalous SST close to South America, Australia, and Southern Africa enforces the wind to go on/offshore and converges/diverges the moisture into/out of the landmass. As a result, specific humidity changes and alters the rainfall over Southern continents on a decadal scale. The scenario is opposite during the negative phase.