Orographic Controls on Precipitation Along the Western Ghats during the Indian Summer Monsoon

This study uses fine-scale meteorological simulations to investigate 1) the role of orography in precipitation along and upstream of the Western Ghats, and 2) a diurnal cycle of precipitation in western India during the summer monsoon. The Weather Research and Forecasting model (WRF-ARW) was used to simulate the 2008, 2009, and 2010 summer monsoons down to 5 km horizontal grid spacing, with initial and boundary conditions provided by ERA-Interim. Preliminary results show that heaviest precipitation in the region is tied to the steep escarpment of the Western Ghats. This finding is in agreement with several recent studies using high spatial resolution TRMM precipitation data, and is at odds with previous studies which suggested an offshore maximum. To determine the role of orography in along-slope and offshore precipitation during active and break periods within the monsoon, metrics such as the low-level cross-barrier wind speed, wind shear, Froude number, and upstream low-level static stability will be evaluated. Output from the WRF-ARW at time increments of 30 minutes allows for analysis of temporal patterns of rainfall and insights into governing mechanisms. Analysis of rainfall rates over these three monsoon seasons reveals a clear diurnal pattern along the escarpment of maximum rates in the early afternoon. Timing of maximum precipitation rates translates into later afternoon and evening hours eastward onto the plateau. No coherent pattern in timing of maximum precipitation is observed in offshore regions.