Entangled Impacts of Large-Scale Monsoon Flows and Terrain Circulations on the Diurnal Cycle of Rainfall over the Himalayas

Abstract

The diurnal features of rainfall over the Himalayas have been widely investigated, but their triggers remain unclear. In this work, we divided the Himalayas and surroundings into four regions, including the plains, foothills, slopes, and plateau, and investigated the above issues. The results show that the rainfall total is controlled by large-scale monsoon flows while its meridional distribution is regulated by terrain circulations. The afternoon rainfall peak in the plains and foothills is linked with the intersection of two monsoon flows. The southward-shifting rainfall peak, which occurs from midnight to early morning in the slopes and foothills, is affected by the nighttime downslope flow and the strong Bay of Bengal monsoon flow in the morning. The evening rainfall peak in the plateau and high-altitude slopes is thought to be a result of the atmospheric layer being at its moistest at that time.