Role of interaction between dynamics,thermodynamics and cloud microphysics on summer monsoon precipitating clouds over the Myanmar Coast and the Western Ghats

Indian summer monsoon circulation can be characterized by mean tropospheric temperature (TT) gradient between ocean and land. Two major heat sources, one near the Myanmar Coast and the other near the Western Ghats play seminal role in defining this TT gradient. While both regions are characterized by very similar orographic features, there are significant differences in frequency of occurrence of precipitating clouds and their characteristics even when the amount of rain in June–July months is almost same in the two regions. Deeper (shallower) clouds appear more frequently over the Myanmar Coast (the Western Ghats). There is a sharp decrease in amount of rainfall from June–July to August–September in both the areas. Rather counter intuitively, during the June–July–August–September season, low and moderate rains contribute more to the total rain in the Myanmar Coast while heavy rains contribute more to the total rain in the Western Ghats. Western Ghats also gets more intense rains but less frequently. With significant differences in moisture availability, updraft, amount and characteristics of cloud condensate in the two regions, this study proposes that the nontrivial differences in features between them could be explained by linkages between cloud microphysics and large scale dynamics. Presence of more cloud liquid water and the role of giant cloud condensation nuclei reveals dominance of warm rain process in the Western Ghats whereas more cloud ice, snow and graupel formation in the Myanmar Coast indicates stronger possibility of cold rain coming from mixed phase processes. Stronger heating caused by mixed phase process in the mid and upper troposphere in the Myanmar Coast and its feedback on buoyancy of air parcel explains the appearance of deeper clouds. Thus, our study highlights importance of mixed phase processes, a major cause of uncertainty in GCMs.