Rainfall characteristics and its variability over a high-altitude station in Western Ghats during southwest monsoon of 2015 - A case study

The rainfall characteristics (orographic and convective) over Mahabaleshwar (MBL), a Western Ghat hill station in India, has been studied in this work. In the first part, the role of orography and convective instability in quantifying rainfall over the station has been examined. In the second part, the variability of rainfall over MBL has been analyzed. In order to estimate orographic rainfall using a 3-D dynamical model, a high-resolution ECMWF reanalysis data was utilized to construct wind and thermal fields at a far upstream location. Whereas, for estimating convective rainfall, the ECMWF reanalysis data and in situ radiosonde data over MBL are used. It is seen that the estimated rainfall using the 3-D dynamical model for orographic rainfall is in good agreement with the pattern of observed daily rainfall as compared to the estimated rainfall using the convective model. Also, the estimated rainfall was able to capture the daily fluctuations in the rainfall. However, the rainfall estimated using the convective model shows much difference in the pattern and magnitude compared to the observed rainfall.Large scale synoptic systems along with aerosols and their characteristics were also examined to understand their influence on rainfall variability. The variability of aerosols and the observed rainfall over MBL reveals that they are significantly correlated.