Statistical characteristics of raindrop size distribution over Western Ghats of India: wet versus dry spells of Indian Summer Monsoon

Abstract. The nature of raindrop size distribution (DSD) is analyzed during wet and dry spells of the Indian Summer Monsoon (ISM) in the Western Ghats (WGs) region by using Joss-Waldvogel Disdrometer (JWD) measurements. The observed DSDs are fitted with gamma distribution, and the DSD characteristics are studied during ISM season (June–September) of 2012–2015. The DSD spectra show distinct diurnal variation during the wet and dry spells. The dry spells exhibit a strong diurnal cycle with two peaks, while the diurnal cycle is not so prominent in the wet spells. Results reveal the microphysical characteristics of warm rain during both the wet and dry periods. Even though the warm rain processes are dominant in the WGs region, the underlying dynamical processes cause the differences in DSD characteristics during the wet and dry spells. In addition, the differences in DSD spectra with different rain rates are also observed. The DSD spectra are further analyzed by separating into stratiform and convective types. Finally, an empirical relationship between the slope parameter, Λ and shape parameter, µ is derived by best fitting the quadratic polynomial for the observed data during both wet and dry spells as well as for the stratiform and convective types of rain. The µ-Λ relations obtained in the present study are slightly different in comparison with the previous studies.