A study on morphology and microphysics of clouds during southwest monsoon over Western Ghats, India, using multi-platform observations

Abstract

Clouds play a significant role in the dynamics and thermodynamics of the atmosphere. To understand the impact of clouds on climate and for better representation of these in the global models, accurate information about the temporal, spatial and vertical distribution of cloud properties such as microphysical, morphological and types are essential. In the present work, vertical structure and microphysics of clouds during southwest (SW) monsoon has been studied from a high altitude site (Mahabaleshwar (17.92°N, 73.66°E, and 1348 m above mean sea level (MSL)) and within ± 0.1 degrees) over Western Ghats, India. Vertical structure of the clouds has been detailed using radiosonde observations. Warm cloud microphysics was investigated using in-situ ground and aircraft cloud measurements. Radiosonde profiles showed the presence of single and multi-layered clouds over the observational site. Higher occurrence frequency for cloud layers below 2 km and above 6 km altitude compared to mid-level clouds (2 to 6 km) during SW monsoon were noticed. Higher occurrences of single layer clouds during June and September (transition period) were noticed whereas frequency of two-layer was higher in July and August (core period). Low (~30%) and high-level (~60%) clouds were dominantly seen compared to mid-level clouds over the observational site during SW monsoon. Warm cloud microphysics was investigated using collocated ground and airborne in situ measurements. Cloud microphysical properties such as cloud droplet number concentration (CDNC), liquid water content (LWC), droplet effective diameter (ED), droplet mean radius (Rm) respectively were analyzed. The cloud liquid water content and the effective droplet diameter showed increase with altitude. Analyzed cloud droplet size distribution (DSD) showed a steep decrease in number concentration of droplets above 25 µm diameters at altitudes above 1800 m, suggesting active collision-coalescence. This is the first such report combining in situ observations from two different platforms to study the vertical structure of monsoon clouds over a complex terrain like the Western Ghats in India.