A new perspective on the distribution of clouds over the Western Ghats using Doppler weather radar observations

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Thursday, 8 January 2015
Subrata Kumar Das, Indian Institute of Tropical Meteorology, Pune, Maharashtra, India; and S. M. Deshpande, K. Chakravarty, and M. C. Kalapureddy

The Western Ghats (WGs) located parallel to the west coast of India receives a huge amount of rainfall during the Indian summer monsoon (ISM) where the topography plays a significant role. With a view to understand the dynamics and microphysics of monsoon precipitating clouds over the WGs, a High Altitude Cloud Physics Laboratory (HACPL) has been operational at Mahabaleshwar (17.92 oN, 73.6 oE, ~1.4 km AMSL) since 2012. As a part of this laboratory, a mobile X-band (9.5 GHz) and Ka-band (35.29 GHz) dual-polarization Doppler weather radar system have been installed at Mandhardev (18.04 oN, 73.87 oE, ~1.3 km AMSL, at 26 km radial distance from the HACPL). These experiments gain its importance in this region due to a greater influence of the south-west monsoon and the observations over the radar site can be taken as a representation of the west coast of India. The X-band radar indicates that the dominant cloud movement is from the western side of the WGs to the eastern side, crossing the HACPL and the radar site. The cloud occurrence statistics show a sudden reduction within a distance of ~30 km on the eastern side of WGs which indicates the possibility of a rain shadow area. Further, the vertical structure of cloud over the HACPL has been investigated, and four cloud modes viz., shallow cumulus mode, congestus mode, deep convective mode, and overshooting convection mode have been identified. The frequency distribution of cloud-cell base height (CBH) and cloud-cell top height (CTH) shows that most of the clouds over this region have a base below 2.5 km and tops usually does not exceed 9 km. This indicates the dominance of warm-rain process in the WGs region. The bright band (0oC isotherm level level) has also been detected and it is found to have a top of ~ 5.3 km, bottom ~ 4.8 km with a thickness of 800 m. It is also observed that with increase in 0oC isotherm level and CTH, increase in surface rainfall rates has been observed. The details will be presented in the upcoming symposium.