Airborne electrical and microphysical measurements in clouds in maritime and urban environments

A study by Khemani and Ramana Murty (1973) has indicated significant increases of rainfall downwind of the urban industrial complex at Bombay during the period of increased industrialisation. In order to understand the physical processes responsible for the observed increases in rainfall, aircraft measurements of cloud electrical and microphysical parameters and of free-air temperatures were made in the maritime (upwind) and urban (downwind) regions at Bombay.The study has pointed out differences in the electrical and microphysical state of clouds in maritime and urban environments. In the maritime clouds the electric field was both positive and negative and the cloud droplet charges were positive. In urban clouds the electric field was negative and the droplet charge was also negative. The cloud condensation nuclei and the total measured droplet concentrations were higher in the urban environment. In urban clouds the droplet spectra showed a multimodal distribution and in maritime clouds it was unimodal. Also, the concentration of large droplets of diameter 50 μm and above, and the integrated cloud droplet liquid water content were more in the urban environment. The tail of the droplet spectra extended to higher sizes in urban clouds. The free air temperature in the urban environment was higher by about 1°C.