Sensitivity of a cloud microphysical model to an urban environment.

Abstract

Observations showed increased concentrations of cloud condensation nuclei (CCN) in air samples collected over and downwind of St. Louis when compared to upwind samples. Aircraft observations of urban clouds showed corresponding increased concentrations of cloud base droplets. Observations indicated higher cloud bases and decreased elevations of average first echo base heights in the St. Louis/East St. Louis area as compared with similar clouds over rural areas. The purpose of this paper is to examine the possible role of CCN chemical competition and number concentration in producing the observed phenomena. The results suggest that the observed differences of depth from cloud base to first echo height between urban and rural clouds do not result from concentration differences in any CCN size range.- from Authors