Multi‐scale variability of the sea surface temperature in the Tropical Atlantic

Abstract

Tropical Atlantic (TA) sea surface temperature (SST) variability is studied using the Continuous Wavelet Transform (CWT) of the SST indices in the Tropical North Atlantic (TNA), Tropical South Atlantic (TSA), and Equatorial Atlantic (EQA). CWT of the difference index (TNSD) between the TNA and TSA indices and the cross‐wavelet spectrum for the TNA and TSA indices are also examined. The analyses focus the short‐interannual, interannual, and decadal scales. The Global Wavelet Power of the TNA, TSA, and EQA indices confirm previous findings on the dominant scales of the SST variability in different TA sectors. The decadal peaks are dominant for the TNA and TSA indices while the interannual peaks are significant only for the EQA index. The scale averaged ΔΦ series for all scales feature a number of abrupt reversals of ±180° which depends on the scale, with larger number for smaller scales. The ΔΦ during the period between two subsequent abrupt reversals remains close to ±180° or varies within sub‐intervals of the −180° to +180° range, thus the dipole‐like, cross‐equatorial SST anomaly gradient, monopole, and equatorial patterns are established as evolving modes. For all scales, the periods of abrupt ΔΦ reversals of ±180° occur within the periods with change in the meridional propagation directions of the SST anomalies or with reduced SST anomalies. This result strongly suggests that the establishment of the SST anomaly patterns in the TA depends crucially on the meridional propagation of the SST anomalies. This is a new aspect not discussed before.