Rain Drop Size Distribution Over a Tropical Indian Station Using Disdrometer

Abstract

Tropical regions can be characterized as large fields of convective clouds of all sizes. Latent heat released is different for different precipitating systems like convective and stratiform. So we need to classify various precipitating systems. In the present study, ground based observations of Joss‐Waldvogel Disdrometer (JWD) which was installed at Thumba (8.5°N, 76.9°E) under Ka band propagation experiment is used extensively to characterize the tropical rain. It can be noticed that the JWD is placed at calm and noise‐free places, in order to make it sensitive to smaller drops. The JWD is a standard tool for precipitation measurements such as Drop Size Distribution (DSD), rainfall intensity, R, rain accumulation and liquid water content, W, reflectivity factor, Z. The range of drop diameters that can be measured spans from 0.3 to 5 mm with an accuracy of 5%. For present study Disdrometer data from June 2005 onwards are collected. The main objective of the present study is to classify precipitation system into Convective, Transition (an intermediate region) and stratiform. Since DSD integral parameters like rain rate (RR), liquid water content (LWC), Reflectivity (Z) are different for different precipitating systems, so we need to classify these systems. There is a dearth of rain drop Size data and distribution models for the tropics, especially over Indian continent. Models for drop size distribution are required for the evaluation of microwave and millimeter wave propagation effects due to rainfall. In the present paper various DSD models namely exponential, gamma and lognormal with different combination of moments for observing the characteristic features of tropical rain are studied. And finally to study the natural variation of DSD with respect to mass weighted mean diameter Dm during stratiform and convective precipitation.