Characterization of raindrop size distributions and its response to cloud microphysical properties

Abstract

Cloud feedbacks continue to alter with climate change, which remains the largest source of uncertainty in global climate. Raindrop size distribution (DSD) is a fundamental characteristic of cloud microphysical and dynamical processes. This study characterizes the DSD and its response to cloud microphysical properties during the Indian Summer Monsoon season (June-October 2013–2015). The derived rain rate varied from 0.50 to 395.4 mm/h, which was segregated into stratiform rain (mean and standard deviation of 2.12 ± 1.24 mm/h) and convective rain (13.10 ± 14.45 mm/h). We found that as the convective DSD mode diameter gradually shifts to a larger drop size with increasing rain rate, the number concentration of small-sized rain drops decreased by about three orders of magnitude. While the mass-weighted mean diameter and normalized DSD scaling parameter were significantly higher for convective rain than stratiform rain, the normalized DSD scaling parameter was lowest for both convective and stratiform rain compared to previous studies over this region. The stratiform DSD was more skewed towards large raindrop size at a high cloud effective radius compared to a low cloud effective radius. However, the opposite response of the DSD for convective rain suggests the predominance of small-sized cloud/ice hydrometeors. This finding was further corroborated by the presence of narrower DSD at high cloud droplet number concentration compared to a low cloud droplet number concentration for the convective rain. The low wind shear and high convective available potential energy for convective rain further substantiated the persistent convective cores during monsoon accompanied by the formation of large size raindrops in the convective systems. Such a distinct response of DSD to different rain regimes could help in the short-term prediction of extreme rainfall events.