Understanding the Monthly Variation in the Upstream Enhancement of Indian Summer Monsoon Precipitation Near the Western Ghats

Located along the western coast of the Indian subcontinent, the Western Ghats mountain range exhibits strong spatiotemporal variability in precipitation. During the summer monsoon season, the Western Ghats experience the heaviest rainfall in the tropics, enhancing regional precipitation along the western coast of India and the adjacent Arabian Sea. Through analysis of satellite and reanalysis data, we found that precipitation enhancement upstream of the Western Ghats is more widespread over the Arabian Sea in June, while precipitation in July and August is more intense but concentrated along the western coastal region. The reason for this monthly variation within the seasonal cycle is unclear. To advance understanding of this precipitation along and upstream of the Western Ghats, we explore a few possible mechanisms for the precipitation seasonality: 1) variability in monsoon onset, 2) the interaction between cross-slope monsoon winds and orography, using new theories for tropical orographic precipitation, and 3) intrusion of climatological low pressure air north of the Arabian Sea. The results from this work will help us disentangle the complex interactions between orography, buoyancy, and convective precipitation that dominate the regional climate of India. A deeper understanding of the drivers of precipitation in this region is crucial to developing robust expectations for how regional precipitation will change in a warmer future climate.