Precipitation processes in southwest India during the summer monsoon: the Orographic Precipitation and Evolution of Landscapes-Western Ghats project (OPEL-WG)

Mechanisms for heavy precipitation near the Western Ghats range in southwest India are an important control on heating and moisture regulation in the broader Indian Summer Monsoon (ISM), as well as the evolution of landscapes and subsequent controls on precipitation on geologic time scales. Motivated by these issues, our field work, observational analysis, and modeling studies aim to better understand the orographic controls on precipitation along the western coast of India.

This study will address dynamical and microphysical mechanisms for heavy precipitation along and upstream of the Western Ghats, including its spatial and temporal distribution using high resolution satellite data from the Tropical Rainfall Measuring Mission precipitation radar (PR) and preliminary results from our 16-site high-resolution gauge network. It is observed that heavy precipitation, originating largely from clouds with echo tops in the mid-troposphere, falls in extremely narrow (5-30 km) zones that are tightly coupled to the spatial distribution of topography. The dynamical regime for the observed precipitation structures will be discussed in relation to our current understanding for mechanisms for orographic precipitation, including the observed lack of precipitation offshore (according to satellite retrievals) that has long been thought to occur over the near-shore Arabian Sea.

We will also present modeling results from simulations using the Weather Research and Forecasting (WRF) Model to examine the performance of the model in representing observed precipitation processes at climate to meso- to cloud-resolving scales. The modeling studies will also be used to address the role of the small spatial scale precipitation processes on the water and energy budgets of the ISM, as well as the ability of models to simulate relevant processes across scales. The role of the land surface in terms of both the terrain forcing and surface fluxes of energy and moisture along the Western Ghats will also be highlighted.