C-band polarimetric Doppler weather radar observations of waterspouts over the southern Indian peninsular coast of the Arabian Sea

Waterspouts are intense, small-scale vortices that develop over water surfaces, typically forming under weak synoptic disturbances combined with localised differential heating. In this study, the three-dimensional structure and dynamical characteristics of two waterspout events observed by the C-band Polarimetric Doppler Weather Radar (C-DWR) at Thumba (8.537°N, 76.865°E) are analysed. The first event occurred near Shangumugham Beach, close to Thumba, during the afternoon of 26 November 2017, two days prior to the passage of Cyclone Ockhi over the region. A second waterspout event, recorded on 24 May 2019, was also clearly captured by the radar system. ERA-5 reanalysis is used to investigate the background characteristics that resulted in the waterspout formation. High spatial and temporal resolution polarimetric radar observations are used to investigate the reflectivity structure and polarimetric characteristics associated with these waterspouts, representing one of the first detailed radar-based analyses of such phenomena over the Indian region. The slanted structure of vortices obtained from the radar reflectivity and velocity measurements provides insights into the three-dimensional evolution of these short-lived microscale circulations. For the first event, the radar observations show a relatively low-reflectivity core surrounding a localised low-pressure centre, producing a hook echo signature. Polarimetric parameters further indicate signatures consistent with convective organisation, including enhanced differential reflectivity and diminished correlation coefficient. Supercell-like characteristics were observed, indicating size sorting and the development of rotational updraft in the storm. These observations highlight the capability of dual-polarimetric radar measurements in identifying structural and microphysical characteristics associated with waterspouts for the first time over the study region.