Modeling of Rain Drop Size Distribution in Association With Convective and Cloud Parameter Over a Tropical Location

Abstract

The difference in raindrop size distribution (DSD) characteristics between convective and stratiform rain and in monsoon and pre-monsoon season have been investigated over a tropical location, Kolkata, using seven years data collected from a Joss-Waldvogel disdrometer. During the Indian Summer Monsoon (ISM) and the pre-monsoon season, Kolkata gets substantial rain. Interannual variability of DSD has been evident. The normalized drop size distributions of DSD show double peak at 20-50 mm/h rain rate due to drop break up and coalescence process. For convective rain, concentration of higher drops (>3 mm) are more significant compared to stratiform rain. In the pre-monsoon period, significant contribution of normalized DSD in the afternoon to late evening has been evident due to nor’westers. Contribution of normalized DSD of higher drops (>3 mm) are more in the pre-monsoon convective rain compared to monsoon convective rain. The larger slope of μ-Λ relationship has been observed in pre-monsoon convective period which corresponds to higher <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> values. The relationship between radar reflectivity ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> ) and rain rate ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> ) distinguishes the monsoon and pre-monsoon seasons. Radiometric measurements have been used to examine the effects of the atmospheric instability parameter CAPE and cloud base height (CBH) on the formation of larger drop sizes. This study will be useful for understanding precipitation microphysics and improving the quantitative precipitation estimation algorithm.