Modeling of Raindrop Size Distribution Observed Using Micro Rain Radar Over Darjeeling (27.05oN, 88.26oE): An Eastern Himalayan Region

Abstract

Micro rain radar (MRR-2) provides the measurement of the drop size distribution DSD with altitude and rain rates. In this paper, we show a new form of gamma drop size distribution (DSD) model. MRR-2 is based on the principle of Radar spectrum measurement of continuous-wave of frequency modulation. DSD measurements for the rain rates ~ 0–25 mm/h and the height from 150 to 2000 m during the south-west monsoon season for the period 2009 and 2010 are used in this study. From the variance of DSD ( $$\sigma^{2}$$ ) and mass-weighted mean drop diameter as well as after the mathematical calculation, two parameters ( $$\varLambda$$ and µ) are obtained for the use of lower-order moments. Both the moments are utilized for the best suitable of gamma DSD. Measured DSD for the different rain rates and different altitudes below the melting layer height (~ 2–3 km) compared among the exponential, lognormal and gamma DSD model over Darjeeling in the Eastern Himalaya. The correlation between best fit measured DSD and gamma distribution indicate that they correlate well for both lower and higher order moments for the heights 150 m and 1050 m. Whereas they correlated only for higher order moments for the 450 m, 1500 m and 1950 m. Thus, it is found that the observed pattern of DSD agrees well to the gamma DSD model.