The evolving influence of local and remote sea-surface temperature variability on the Asian monsoon during the last century

During the last century, the warm pools of the tropical oceans have increased substantially in association with global warming. Waters warmer than 28C have increased by almost 70% globally and large changes have occurred in the Indian Ocean. We consider whether these changes to the warm pool are associated with secular changes in precipitation over the monsoon regions. The Simplified Parameterization Primitive Equation Dynamics (SPEEDY) model is used to explore how these changes in sea surface temperature (SST) influence the Asian monsoon dynamics. To gain a better understanding of the interaction between SST and monsoon dynamics, five experiments are designed using different sets of prescribed sea surface temperature. An analysis of the runs reveals that warmer SST in the Indian Ocean and Pacific Ocean basins produce a decrease in precipitation in the eastern Indian Ocean and south eastern China. We also explore how anomalous SST affects the dynamics indexes of the monsoon. Results indicate that the zonal monsoon index (a measure of monsoon intensity) decreases under the warmer SST scenario, implying a weaker monsoon circulation. Additionally, surface winds weaken in both the summer and winter monsoon. The Asian monsoon is found not only to be influenced by local variations of SST but by changes in Pacific Ocean SST as well. Regions most affected by Pacific Ocean SST are the Bay of Bengal, the southern Indian Peninsula, which exhibit stronger monsoon characteristics for cold Pacific Ocean SST anomalies, and the Western Indian Ocean, which shows an increase in the monsoonal circulation and precipitation for warmer Pacific Ocean SST conditions.