Microphysical characteristics of rainfall during different seasons over a coastal tropical station using disdrometer

Abstract

AbstractDrop size distribution (DSD) over the tropical region exhibit pronounced variations during different monsoon seasons. Measurements from an impact type Joss–Waldovgel disdrometer is used for characterization of drop size distribution and its integral parameters over a tropical coastal station (Thiruvananthapuram, 8.31°N, 76.54°E, 20 m asl). Rain events were identified during the winter, premonsoon, summer monsoon and postmonsoon seasons from 8 years, computed rain duration (min) and accumulated rain water (mm). Rain intensity (mm h−1), mean drop diameter (Dm, mm) and total number concentration of raindrops (NT, m−3) were calculated on each sampling interval and classified in to different bins.The different range bins of rain intensity and their relative contributions towards total rainfall are different for different seasons. Maximum events were reported on the R2 (heavy drizzle/light rain) type, but the contribution of rainfall (mm) is mainly registered on R4 (heavy rain) type. Similarly, the NT and Dm are also showing different characteristics during different monsoon seasons. Frequency of occurrence of Dm is higher in Dm2 (1–2 mm) followed by Dm1 (Dm < 1 mm) and then Dm3 (2–3 mm) with difference in magnitudes for different seasons. On analysing relative rainfall contribution from different mean diameter bins, it can be observed that Dm2 and Dm3 (1–3 mm) are the major contributors to the total rainfall. In the case of NT, both frequency and accumulated water are almost same or comparable for the different bins during all the seasons. The Dm and NT are positively related with different intensity bins. The lower rainfall intensity bins show higher duration during the summer monsoon season and lower duration during the premonsoon season, the higher intensity range bins show lower duration for the premonsoon season and higher duration for the postmonsoon season.