Unprecedented cross-equatorial southerly wind anomalies during the 2020–2023 triple-dip La Niña: Impacts and mechanisms

The 2020–2023 La Niña event, the third triple-dip occurrence since 1950, stands out for its unique characteristics when compared to the preceding events in 1973–1976 and 1998–2001. Unlike its predecessors, the latest event emerged without a preceding strong El Niño episode, starting from a state of weak discharge. Moreover, the resurgence of cold sea surface temperature (SST) anomalies during 2020–2023 showed a loose link to ocean-atmosphere variability in the northern subtropical Pacific. The spatial pattern of anomalous conditions in this recent event featured persistent SST cooling in the southeast tropical Pacific, accompanied by pronounced meridional southerly wind anomalies. Our comprehensive investigation indicates a minimal role of subsurface ocean dynamics, underscoring the exceptional strength of cross-equatorial meridional southerly wind anomalies as a primary driver of sustained negative sea surface temperature anomalies. By considering the influences of intra-basin and inter-basin factors, we propose that the observed patterns may be the combined outcome of interannual variability within the tropical Pacific and decadal variations beyond the tropics. Noteworthy contributions from the low-frequency components of the South Pacific Meridional Mode and the Atlantic Warm Pool further shape the dynamics of this event. Our findings underline the increasing importance of meridional winds in shaping the evolution of ENSO in recent decades.