The southern tropical Indian Ocean Dipole (STIOD) is a key mode of Indo–Pacific climate variability, distinct from the canonical Indian Ocean Dipole, whose driving mechanisms have changed in recent decades. Here we show that STIOD events occurred nearly twice as often before 2000, reflecting a fundamental shift in their triggering processes. Prior to 2000, STIOD events were jointly triggered by the Australian winter monsoon and El Niño–Southern Oscillation (ENSO). After 2000, ENSO forcing weakened markedly, and STIOD variability became primarily controlled by the Australian winter monsoon. This transition arises from pronounced background SST warming near northern Australia, together with cooling in the tropical eastern Pacific and an increased frequency of late–developing CP El Niño events. The former enhances Australian winter monsoon–induced convection and associated Gill–type atmospheric responses, whereas the latter suppresses ENSO–related convection and weakens the Walker circulation. These results demonstrate how mean–state changes and ENSO diversity jointly reshape Indo–Pacific air–sea coupling.
 

Indian Ocean Dipole,ENSO,Australian monsoon