Deposition ice nuclei observations during CAIPEEX

A thermal gradient diffusion chamber (TGDC) designed to process the ice nuclei (IN) sample is illustrated with unique airborne observations. IN samples collected during the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) have been analyzed using the TGDC. The TGDC is able to activate the IN by deposition mode over ice supersaturation of 6-24% and at a temperature range of 18.5 to 13.5 C. These samples correspond to first observations at several vertical levels including the cloud layer and over several geographically distinct locations in India during the monsoon season. Vertical profile of IN concentration shows that at a given level, there is large spatial and temporal variation in IN concentration. Maximum IN concentrations are observed below 3 km at all ice supersaturation. Highest IN concentrations are noted over inland continental regions. Spatial variation in IN concentration was observed in the range 0 to 5 L-1 with an average of 1.12 L-1 at highest ice supersaturation (20-25%) interval. Large variation in IN concentration at a single temperature is also observed. Our observation shows that there is a significant increase in IN concentrations with supersaturation over ice. Elemental chemical analysis of the collected aerosol samples by Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectrometry (EDX) showed that copper, silica, aluminium and zinc are the most abundant elements. (C) 2014 Elsevier B.V. All rights reserved.