Microphysical characteristics of shallow precipitating systems in the southwest monsoon season: An analysis using in-situ and remote sensing observations

Abstract

The present study examined the microphysical features of the shallow precipitating systems at low (10.04°N, 76.33°E, 20 m above MSL) and mid-altitude (8.45°N, 77.5°E; 400 m above MSL) locations situated on the windward side of the Western Ghats in southwest monsoon 2019. A total of 226 and 336 shallow precipitating systems were identified using radar reflectivity and surface rain rate from the co-located measurements using the micro rain radar and disdrometer instruments in both locations. The average cloud base height of shallow precipitating systems is ∼1 km. An elevated cloud layers (0.8–3.8 km) during long-duration shallow precipitating systems are more prevalent in low-altitude location. Shallow events in the mid-altitude region are characterized by long durations and high surface rain rates. Based on the duration and rain rates, the shallow systems are further classified for in-depth microphysical analysis. The broader raindrop size distribution spectra are clearly observed for the shallow events having higher duration and intensity. The concentration of small size raindrops are higher across all rain categories in the low-altitude location, while the concentration of mid-sized raindrops is notably higher in the heavy rain category indicating an active collision-coalescence process. Light rain events are predominantly characterized by small raindrops (D < 1 mm), whereas moderate and heavy rainfall events are primarily composed of midsize raindrops (1 ≤ D < 3 mm). The Nw-Dm relation for the shallow events in wet (dry) spells suggests that, isolated events mainly occur due to the local orographic effects of the elevated terrains.