Drivers of Wetter South Asian Summer Monsoon in the 21st Century

Tuesday, May 13, 2014 - 07:00
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We analyze a suite of GCMs from the 5th Phase of Coupled Models Intercomparison Project (CMIP5) archives to understand the mechanisms behind a net increase in the South Asian summer monsoon precipitation in response to stronger radiative forcing during the 21st century despite a robust weakening of the governing thermodynamics. Combining the future changes in the contributions from various moisture sources, which contribute to the moisture supply over South Asian landmass, with those in monsoon thermodynamics and atmospheric moisture content, we establish a pathway of understanding that partly explains these counteracting responses to increase in radiative forcing.  Our analysis suggests South Asian summer monsoon receives moisture from regional (local recycling, Arabian Sea, Bay of Bengal) and remote (rest of the globe) sources that is facilitated over land by monsoon thermodynamics. Increase in radiative forcing fuels an increase in the atmospheric moisture content.  For regional moisture sources, the effects of excessive atmospheric moisture are offset by weaker monsoon thermodynamics as all of them show a net decrease in their relative contribution to the total moisture supply during summer season. However, weakening of monsoon thermodynamics has little effect on the moisture supply from remote sources that not only is a dominant moisture source in the baseline period, but is also the net driver of the positive summer monsoon precipitation response in the 21st century.

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