Structure and evolution of organized precipitation bands: C-band doppler weather radar observations over Thumba (8.5o N, 77o E)

Abstract

In the present communication, C-band polarimetric Doppler Weather Radar (C-DWR) observations are used to investigate the structure and evolution of organized precipitation bands during the Indian summer monsoon (ISM) of 2017, 2018 and 2019 over Thumba (8.50 N, 770 E), a coastal location in south India. The C-DWR observations show organized high radar reflectivity structures of ∼50 dBZ that organized into narrow bands of ∼200 km (North-South) in length and 10–20 km (East-West) in width with vertical extent of ∼6–8 km. These narrow bands of precipitation structures are observed to be formed over the Arabian Sea and subsequently propagating towards the radar site. The observed differential radar reflectivity (Zdr) and the correlation co-efficient values indicate the horizontally oriented droplets and non-uniform hydrometeors. The potential formation mechanisms of the precipitation bands are investigated using reanalysis winds. The results show that blocking effect induced by the Western Ghats around the radar site play a key role in the formation of organized precipitation bands. It is noted that the location of the blocking effect induced convergence (conducive for the formation of precipitating clouds) with respect to the orography is proportional to the intensity of the low-level winds. The significance of the present study lies in understating the structure and evolution of organized precipitation bands and discussing their potential formation mechanisms during the ISM using C-DWR observations.