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

• Published in: Geophysical research letters Vol. 49; no. 16
• Main Authors: Senapati, Balaji, Dash, Mihir K., Behera, Swadhin K.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.08.2022
• Subjects: Atmospheric circulation; Continents; decadal variability; Decadal variations; Decay; EEMD; Empirical analysis; Function analysis; Moisture effects; Oceans; Offshore; Orthogonal functions; Precipitation; Rainfall; Rainfall variability; Sea surface; Sea surface temperature; Southern continental rainfall; Specific humidity; SPMM; SST footprints; Surface temperature; Variability; Wavelengths; wavenumber‐4 pattern; Indian Ocean; South Pacific; Australia
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL099046

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. Plain Language Summary The sea surface temperature (SST) has four positive (negative) loading centers located in the South‐central Pacific, South‐western Atlantic, South‐western Indian Ocean, and South of Australia (South‐eastern Pacific, South‐eastern Atlantic, South‐eastern Indian Ocean, and South‐western Pacific Ocean), called a wavenumber‐4 (W4) pattern in the southern subtropics. It is generated due to a coupling with a similar W4 pattern seen in the atmosphere. Apart from year‐to‐year variation, this W4 pattern also has a decadal cycle and is reported in this study. The reason behind this is mainly linked to the decadal variation of the South Pacific Meridional Mode (SPMM). When the SPMM decays, it leaves some SST signals over the South Pacific Ocean which remain for a longer time and lead to SST W4 having more positive/negative events in one decade compared to others. The resulted SST W4 pattern affects the Southern continental rainfall by controlling the local atmospheric circulation. Key Points Decadal variability in sea surface temperature (SST) wavenumber‐4 (W4) pattern is revealed over southern subtropics (20°–55°S) The footprinting mechanism and SST residuals from the South Pacific Meridional Mode lead the SST W4 decadal variability by 2 years SST W4 potentially affects the decadal rainfall variability over Southern continents by modulating local atmospheric circulation