Intriguing aspects of rainfall initiation over rainshadow region during boreal summer monsoon

Abstract

This novel study explains a plausible physical mechanism for rainfall initiation over the southeast peninsular India (SEPI, referred to be a ‘rain shadow’ region) during the southwest monsoon season. Further, the contrasting rainfall patterns between the rain shadow region and central India (CI) are also elucidated through the response of the maritime continent (MC) convection. MC is found to be a prominent source for the initiation of wet spells over the rain shadow region (during which CI is in dry phase), with the rainfall anomalies over MC leads SEPI by ~5–7 days. Evolution of convective anomalies resembles a classical Gill-type response, with a pair of Rossby waves on the poleward side of the convection center and Kelvin waves on the eastern side. Thus, the combined effect of large-scale circulation and moisture anomalies over MC contributes to the preconditioning and subsequent positive rainfall anomalies over the rain shadow region.