Satellite-based insights into the detrimental impact of smoke and air pollution on precipitation (Invited Presentation)

A new generation of satellites with new sensors is providing new capabilities for simultaneous measurements of the necessary ingredients for monitoring the cloud-aerosol interactions and their impact on precipitation. The Tropical Rainfall Measuring Mission (TRMM) has on board Visible and IR sensor (VIRS), used for obtaining the evolution of cloud particle size with cloud top temperature (T). The TRMM Microwave Imager (TMI) is used for obtaining cloud water contents and precipitation. The TRMM Precipitation Radar (PR) is used for direct measurements of the precipitation radar reflectivity. Other satellites and sensors, such as NOAA/AVHRR, Terra and Seawifs, provide products of aerosols and cloud parameters. The methodology making use of these measurements to obtain insights into cloud microstructure and precipitation forming processes is reviewed. Application of this methodology has revealed that smoke from burning vegetation, urban and industrial air pollution affects clouds by reducing their droplet size and suppressing coalescence. The minimum cloud depth for the onset of precipitation was considerably higher in polluted clouds as compared to nearby pollution-free clouds. Furthermore, the pollution was shown to suppress also ice precipitation processes. The satellite methodology has been used also to infer the existence of supercooled water in vigorous convective clouds with suppressed coalescece down to nearly -38oC. These satellite inferences have been validated by in situ aircraft measurements. This underscores the profound impact that the intensity and extent of coalescence has on cloud microstructure and precipitation, not only from shallow clouds, but also from deep cumulonimbus clouds. The implications of these findings for both inadvertent and advertent weather modification are discussed.