Why Does the Monsoon Rainfall Increase Over South Asia and Decrease Over the Indian Ocean in a Warming Planet?


Climate models project an increase in the mean precipitation over south Asia under global warming. This increase in continental rainfall over Asia is associated with a decrease over the equatorial Indian Ocean rainfall. With a simplified atmospheric model, DOE funded scientist, Dr. Annamalai, highlights processes involved in the connection between the equatorial Indian Ocean and south Asian precipitation. A diagnosis of the moisture and energy budgets reveals that the transport of moisture by winds contributes the most to the budget of moisture over south Asia. Specifically, the anomalous (deviation from the climatological mean) winds that originate in the equatorial Indian Ocean transport air of higher moisture content from the equatorial Indian region, to south Asia, increasing precipitation over South Asia. Consequently, the two regions are connected by a thermally driven circulation pattern. These results imply that in coupled models, realistic representation of the climatology and details of the moist processes are necessary for successful monsoon prediction.


H Annamalai, 2010: Moist dynamical linkage between the equatorial Indian Ocean and the South Asian Monsoon Trough, J. Atmos. Sci., Vol. 67, 589-610.