Interannual Variability of the Australian Summer Monsoon Sustained through Wind-Evaporation Feedback in the Tropical Southeastern Indian Ocean

In austral summer, interannual variability of convection is centered around Indonesia and northern Australia, representing significant variability in the Australian summer monsoon (AUSM). It is known that interannual variability of seasonal-mean AUSM activity is hardly forced locally and remotely by tropical sea surface temperature (SST) variability, which results in lower seasonal predictability of precipitation around northern Australia. This study reveals that internal variability unforced by tropical SST anomalies is dominant in seasonal mean strength of the AUSM system. Our analysis suggests that under the climatological monsoonal westerlies in austral summer, the wind-evaporation feedback in the tropical southeastern Indian Ocean sustains anomalous convection despite a counteracting local effect by weak SST anomalies. The wind anomalies induced by the anomalous AUSM modify the subsurface southeastern Indian Ocean, which can contribute to the maintenance of the anomalous convection through weakening the damping effect by SST anomalies. The anomalous AUSM activity also forces a distinct wavetrain pattern from the MC toward the extratropical North Pacific to modulate the East Asian winter monsoon, limiting seasonal predictability for wintertime East Asia.