Role of Indochina Peninsula topography in precipitation seasonality over East Asia

Stage-wise precipitation evolution over East Asia, primarily from spring to summer, is influenced by nearby monsoons and can be topographically driven. Corresponding to the onset of the Asian summer monsoon circulation, the Meiyu-Baiu occurs rapidly in May, replacing the East Asian spring rains. The Meiyu-Baiu rapidly terminates in late July due to the synchronous development of the subtropical monsoons extending from Africa to the East Asia-Western North Pacific (WNP). In late summer-autumn, the monsoonal circulation gradually retreats, in contrast to the rapid and stepwise transitions of the monsoon. This study reviews the role of the Indochina Peninsula in modulating the seasonality of nearby monsoons, primarily based on previous modeling works, and expands the analysis for a full view of the annual monsoon cycle. The review and additional results highlight the role of the topographical processes of the Indochina Peninsula in driving the rapid monsoonal transitions, which correspond to the early summer vertical circulation coupling over the Bay of Bengal-Indochina Peninsula and the late-July WNP monsoon onset. In the simulation with a flattened topography, the southerly winds disappear over the Indochina Peninsula and the westerly winds gradually expand eastward across the Indochina Peninsula in the lower troposphere.