SST-Rainfall Relationship

SST-rainfall relationship within the realms of the Asian Monsoon, in a changing climate
It was thought that the monotonous increase of precipitation with respect to sea surface temperature (SST) is limited to an upper threshold of 28-29°C, over the monsoon basins. Based on this assessment it has often been presumed that, since the mean SSTs over the Asian monsoon basins (Indian Ocean and north-west Pacific, Fig. 1) are mostly above the threshold, SST does not play an active role on the summer monsoon variability.

Mean SSTs over Arabian Sea, Bay of Bengal and the South China Sea, during June-SeptJune-September mean summer SST over the Indian Ocean and the west Pacific

Revised SST-rainfall relationship
The current study shows that the response of precipitation to SST has a time lag, that too with a spatial variability over the monsoon basins. Taking this lag into account, the study finds that there is no upper threshold, and that precipitation continues to increase, even at the highest possible SSTs over the tropical monsoon basins (Fig. 2). This helps in quantifying the SST-precipitation relationship – a 1°C rise in SST corresponds to a 2 mm/day increase in precipitation. The quantification and the process study is useful in understanding the fate of the Asian monsoon in future climate scenarios, with warmer SSTs over the tropical oceans.

 SST-rainfall relationship over the tropical oceans and the monsoon domain 
Media Highlights: The study was highlighted in the Science & Technology section of a leading newspaper [article]

Roxy M., 2013: Sensitivity of precipitation to sea surface temperature over the tropical summer monsoon region—and its quantification. Climate Dynamics, 43, 5-6, 1159-1169 [pdf]