THE IMPACT OF INDIAN OCEAN SST ON THE LARGE-SCALE ASIAN SUMMER MONSOON AND THE HYDROLOGICAL CYCLE

Abstract

Relationships among the large-scale hydrological cycle, Asian summer monsoon and Indian Ocean sea-surface temperature (SST) anomalies are investigated in a series of numerical experiments. Ensembles of integrations with the National Center for Atmospheric Research community climate model, CCM 1, focusing on the summer months (June, July, and August) provide the basic information for analysis. Impacts of SST anomalies in the southern Indian Ocean are evaluated by intercomparison of experiments with and without these anomalies. Systematic changes in the hydrological cycle and monsoon circulation are demonstrated and summarized in the context of a three-dimensional framework consisting of the basic elements of the Asian summer monsoon system. In the negative SST anomaly case, both the hydrological cycle and circulation processes are enhanced by virtue of their close relationship and especially the inherent coupling between the large-scale water vapour transport and the low-level monsoon flow. The overall intensity of the broad-scale monsoon, in this case, is enhanced. In the positive SST anomaly case, the model response is essentially opposite to that of the negative case and the intensity of the broad-scale monsoon is reduced. These enhanced/weakened monsoon scenarios share many similar features to observed interannual variations of the Asian summer monsoon.