Are winds and moisture necessary to cause Indian summer monsoon extremes?

The extremes of Indian summer monsoon rainfall (ISMR) are largely driven by the modulation of vertically integrated moisture flux over the Arabian sea (70^oE) and the Bay of Bengal (90^oE). The droughts and floods are resulted due to strong divergence and convergence of the moisture-laden winds over India associated with various external forcings. Therefore, identifying the association of the zonal moisture flux with ISMR in the observation and Climate Forecast System version 2 (CFSv2) model is essential to improve the prediction of the ISMR extremes. We find that, unlike observation, ISMR extremes in CFSv2 are all ENSO-related and mainly driven by the moisture flux over the Bay of Bengal and remain unresponsive to eastward boundary flux at 70^oE. Further decomposition of the fluxes into dynamical (winds) and thermodynamical (moisture) components shows that both moisture and winds terms over the Arabian sea are necessary for determining extremes. However, in CFSv2, only the winds component of the eastern boundary (90^oE) flux plays a significant role in driving the ISMR extremes. It is due to the presence of strong heating over the Western Pacific which results in strong eastward moisture flux over the Bay of Bengal through a Gill-type response.