The role of water vapor in driving the centennial-scale oscillation in monsoon

Abstract:

Various proxies and climate model experiments have documented the impact of abrupt fluctuations in the strength of Atlantic Meridional Overturning Circulation (AMOC) on the Indian monsoon. Using the energetic framework of monsoons, we have proposed a new diagnostic model to unravel a mechanism. This diagnostic model delineates the variations in precipitation into a contribution from water vapor, net energy flux into the atmosphere, and vertical moist stability (VMS). VMS is the difference in the moist static energy between the upper and lower troposphere. Hence it represents the vertical energy stratification. This model accounts for the two different effects of water vapor on precipitation: as a source of moisture and its effect on vertical stability. We find that the impact of AMOC on the Indian monsoon is primarily through the influence of water vapor on the vertical stability of the atmospheric column. These variations in water vapor are due to variations in sea surface temperature (SST) in the Indian Ocean, which are linked to SST in the North Atlantic. This mechanism is consistent with that indicated by other studies. Thus, elucidating the convenience of the diagnostic model in analyzing the output of long transient simulations.