The role of air-sea interaction over the Indian Ocean in the in-phase transition from the Indian summer monsoon to the Australian boreal winter monsoon

Abstract

The Indian Ocean sea surface temperature (SST) can affect the regional climate in the surrounding regions, including the Indian summer monsoon (ISM) and the Australian summer monsoon (ASM) variability. Recently, it was demonstrated that the in-phase ISM-to-ASM transition can be accomplished through monsoon-Indian Ocean interaction solely. To investigate this issue, a long-term simulation of a hybrid coupled model (HCM) is conducted, in which the atmospheric general circulation model is coupled with a slab ocean model in the Indian Ocean only. Air-sea interactions are allowed only in the tropical Indian Ocean, and the climatological sea surface temperature is specified outside the tropical Indian Ocean. Results from the idealized simulation indicate that the Indian Ocean SST itself can induce in-phase ISM-to-ASM transitions. A wet ISM is largely associated with cool SST in the tropical South Indian Ocean in summer. A wet ASM is also associated with cool SST anomalies in summer. These cool SST anomalies persist until fall and lead to anomalous downward flows over the center of the tropical South Indian Ocean. Consequently, anomalous low-level convergences dominates over northern Australia until winter, which induces a wet ASM.