Role of Orography, Diurnal Cycle, and Intraseasonal Oscillation in Summer Monsoon Rainfall over the Western Ghats and Myanmar Coast

A key finding from this study is that rainfall maxima over the Western Ghats (WG) and Arakan Yoma (AY) during the Asian summer monsoon are located on the upslope of WG and along the coastline of AY, contrasting with offshore locations reported in prior studies. The research used 16 years of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar data to analyze diurnal cycles and intraseasonal oscillations. It revealed distinct rainfall patterns: continuous rain with slight nocturnal and afternoon–evening peaks over WG, and an afternoon peak on the upslope with a morning peak off the coast in AY. Strong environmental flow perpendicular to coastal mountains correlates with large rainfall amounts and small diurnal amplitudes. Additionally, the boreal summer intraseasonal oscillation (BSISO) introduces a southwest wind anomaly that enhances orographic rainfall over WG, causing a phase lag between rain anomalies and northward-propagating major rainbands—a phenomenon absent in AY due to more closed cyclonic circulations.

Shige, S., Nakano, Y., & Yamamoto, M. K. (2017). Role of Orography, Diurnal Cycle, and Intraseasonal Oscillation in Summer Monsoon Rainfall over the Western Ghats and Myanmar Coast. Journal of Climate, 30(23), 9365–9381. https://doi.org/10.1175/jcli-d-16-0858.1