Cloud radar observations of multi-scale variability of cloud vertical structure associated with Indian summer monsoon over a tropical location

Abstract

Tropics nurture three different types of convective clouds, i.e., shallow cumulus, cumulus congestus, and deep cumulonimbus. The vertical structure of clouds holds a crucial metric in studying tropical clouds. Ground-based high-resolution cloud radar measurements are the potential candidate in exploring the characteristics of various types of tropical clouds and their evolution. Quality-controlled cloud radar data containing a total of five million vertical profiles of equivalent reflectivity factor (VPR) are used to examine the intra-seasonal variation of cloud vertical structure (VSC) during the Indian summer monsoon (ISM) over Mandhardev (18.04° N, 73.87° E, and ~ 1.3 km AMSL) in the Indian Western Ghats. The cumulus congestus (Cc) in the transition of shallow to deep clouds is investigated for the first time using the hourly VPR data for 60 consecutive ISM days. Mid-level moistening plays a vital role in this non-precipitating shallow to precipitating congestus transformation and increment of the rain accumulation. Low cloud reflectivity distribution can distinguish precipitating and non-precipitating clouds that help to classify the observed monsoon as normal or below normal. More than 150 mm of rain accumulation during ISM is associated with more than 22% of high clouds. This particular aspect indicates that cold rain processes are essential to assess the ISM over the observational site. FFT analysis on the time series of low-, mid-, and high-level cloud regions with the VPR shows prominent intra-seasonal variability of 5–10, 10–20, and 30–60 days periodicities. This study highlights the significance of VSC over tropics pertinent to the monsoon large scale atmospheric condition.