Balloon-borne Measurements of Cirrus Clouds over Hyderabad during BATAL Campaign.

Clouds significantly impact Earth's radiation budget and hence its climate. Radiative effects of clouds depends on their macrophysical (altitude, coverage and thickness) and microphysical properties (number concentration, size and shape-distributions of cloud droplets/ice-crystals). However, the microphysical representation of clouds, especially the extremely cold and thin cirrus clouds in the global climate model is poor owing to the uncertainties involved in the size distribution and number concentration of ice-crystals having diameter less than 100 µm (Heymsfield et al., 2017). The mechanisms involved in their formation, maintenance and decay are also not well understood.

Under the framework of Balloon measurement campaigns of Asian Tropopause Aerosol Layer (BATAL), size distribution of cloud droplets and ice-crystals inside cloud layers were measured over TIFR Balloon Facility, Hyderabad (17.47˚ N, 78.58˚ E), India by using an optical particle counter called Boulder Counter. Boulder counter can count particles having diameter of 5, 10, 25, 40, 50 and 100 µm. Simultaneous measurements from Boulder counter and a backscatter sonde called COBALD reveal the presence of multi-layered clouds with a cirrus cloud layer located at extremely cold conditions (-86˚ C) of tropopause. Base and top of this cloud layer were mostly composed of small ice-particles having diameters of 5 and 10 µm with particle number concentrations between 80-100 particles per Litre. However, larger ice-crystals of diameters between 25 and 40 µm were also found near cloud base at concentrations of 1-10 particle per Litre indicating towards sedimentation and aggregation. This study also investigates the formation mechanism of different layers of clouds using back-trajectory analyses and their intersection with convection.