Decadal changes in the Southern Hemisphere sea surface temperature in association with El Niño–Southern Oscillation and Southern Annular Mode

Abstract

The spatial structure of El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM), which are the two most important climate modes affecting sea surface temperature (SST) variability in the Southern Hemisphere (SH), appear to have changed since 1999. The characteristic features of the ENSO- and SAM-related atmospheric and oceanic variability in the SH are compared between two sub-periods (1979–1998 and 1999–2012) using cyclostationary empirical orthogonal function analysis. During the earlier period of 1979–1998, the ENSO is characterized by conventional eastern Pacific type, in which the signals in the SH constitute the Pacific South America teleconnection pattern. In contrast, due to a shift of the active center of ENSO to the central Pacific in the later period (1999–2012), atmospheric circulation and SST variability over the SH significantly vary. Moreover, the SAM-related SST variability also shows remarkable differences before and after 1998–1999. This difference is primarily attributed to differences in the non-annular spatial component of the SAM between the two periods. Due to the changes in the spatial structure of the SAM, as well as those of the ENSO, SST variability in the SH displays a marked change between the two periods. Detailed descriptions of the decadal changes of the SH SST in terms of interaction in the oceanic and atmospheric variability are presented along with the possible implications of this change.