A Study of hailstorm of 19th April 2010 over Delhi using Doppler Weather Radar observations

Hailstorm of 19th April 2010 over Delhi has been studied using observations from Doppler Weather Radar (DWR) installed at Palam. The data was analysed at Central Server located at India Meteorological Department HQ using IRIS software (of M/s SIGMET-VAISALA, Finland) installed in the server. Reflectivity of 45 dBZ level was found to be 6.3 km above freezing level at the time of hailstorm which corresponds to 100% (obtained from probability function diagram of Witt et al. (1998)) probability of hail. Reflectivity was more than 55 dBZ upto 10 km and 7 km at 1110 UTC and 1120 UTC respectively which exceeds the hail threshold limit adopted in NEXRAD (USA). Maximum of 62 dBZ was observed at about 3 km at 1110 UTC and 64 dBZ at 3.5 km at 1120 UTC in Radar Data. Very high values of Vertical Integrated Liquid (VIL) ranging from 58.7 kg/m2 to 64.1 kg/m2 were observed between 1040 UTC and 1120 UTC which is higher than 43 kg/m2, the threshold value for occurrence of hail. Severe Hail Index (SHI), Probability of Severe Hail (POSH) and Maximum Expected Hail Size (MEHS) were computed to verify the applicability of enhancedHail Detection Algorithm (HDA) outlined by Witt et al. (1998) to Indian conditions. The Maximum Expected Hail Size (MEHS) computed using Doppler Weather Radar observations were 2.5 cm, 2.6 cm and 2.0 cm respectively at 1050 UTC, 1100 UTC and 1110 UTC which are in close agreement with the reported hail size. The study confirms that HDA and other thresholds of reflectivity and VIL used for hail detection and warnings in NEXRAD (USA) can be used in Indian conditions also.