Monday, 10 January 2005: 10:45 AM
Urban and Industrial Aerosols Impacts on Precipitation
The recent satellite observations of “pollution tracks” devoid of precipitation in clouds downwind of urban and major industrial areas provided the first evidence on the role of pollution aerosols on suppressing precipitation. Subsequent analyses of rain gauge time series quantified these effects in winter orographic precipitation downwind of urban areas, and showed decreases ranging from 10 to 25% on an annual basis. The effects are more complicated for precipitation from thermally drivel (convective) clouds. The initial suppression of precipitation delays the onset of precipitation and allows the clouds to grow larger and more vigorous before start precipitating. This leads to more intense showers and thunderstorms. The enhanced precipitation over and downwind major urban areas such as Houston may be a combined result of this aerosol effect and the heat island effect. The evidence will be reviewed, as obtained from satellite and ground based observations and from model simulations.