Role of Narrow Mountains in Large-Scale Organization of Asian Monsoon Convection*

Abstract The Asian summer monsoon is organized into distinct convection centers, but the mechanism for this organization is not well understood. Analysis of new satellite observations reveals that narrow mountain ranges are an important organizing agent anchoring monsoon convection centers on the windward side. The Bay of Bengal convection, in particular, features the heaviest precipitation on its eastern coast because of orographic lifting as the southwest monsoon impinges on the coastal mountains of Myanmar (also known as Burma). This is in contrast to the widely held view that this convection is centered over the open ocean as implied by coarse-resolution datasets, a view that would require an entirely different explanation for its formation. Narrow in width and modest in height (≤1 km), these mountains are hardly mentioned in conceptual depictions of the large-scale monsoon and poorly represented in global climate models. The numerical simulations of this study show that orographic rainbands are not a local phenomenon but exert far-reaching effects on the continental-scale monsoon. The realization that these overlooked geographical features are an important element of the Asian monsoon has important implications for studying the monsoon in the past, present, and future.