Diurnal Variation of Rain Drop Size Distribution over the Western Ghats of India

Joss-Waldvogel Disdrometer (JWD) measurements at the High-Altitude Cloud Physics Laboratory (HACPL: 17.56°N, 73.4°E, above 1373 m MSL), Mahabaleshwar were investigated for determining the diurnality of the drop size distribution (DSD) associated with the precipitation characteristics over the Western Ghats of India. The JWD data for the period from 2015 to 2019 were collected and examined during the Indian Summer Monsoon (ISM) season. The number concentration of rain droplets of various diameters is considerably varying with the rain rate (R) and type of precipitating cloud. With increasing the value of R, rain droplets having larger diameter concentration significantly increases, and the distribution tail moves towards the biggest droplets. The average value of reflectivity (Z), R, liquid water content (LWC), mass-weighted mean diameter (Dm), and normalized intercept parameter (log10Nw) was found to be higher for the heavy rainfall (Rhigh ≥10 mm h-1) as compared to the low rainfall (Rlow < 10 mm h-1) during the entire study period. The gamma distribution of DSD shows significant differences during the low and heavy precipitation on different time periods (e.g., 00-06, 06-12, 12-18, 18-23 LST). The number of rain events contributing to the total accumulated rain varies with time. The maximum number of rain events occurred during 12-18 LST, with 23.6 % rain events of low rainfall and 4.9% of heavy rainfall. The bimodality is observed in the diurnal variation of Dm, R, and Z, with the largest peak recorded in the late afternoon hour (13-16 LST) and the second crest in the early morning hour (05 LST). At the same time, the log10Nw value drops down, indicating the lowest concentration of rain droplets.