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The accomplishments in addressing Objective 1 include:

  • Documentation of the regional aerosols, including pollutants from urban and industrial sources, and the effects of these aerosols on cloud structure and behavior.

  • Demonstration that CCN aerosols, on which cloud droplets form, constitute about 10% of the overall regional atmospheric aerosols

  • Documentation that the Sierra Nevada often receives precipitation from shallow pristine clouds as long as they do not ingest pollutants from the atmospheric boundary layer.

  • Demonstration that high concentrations of tiny CCN aerosols inhibit precipitation when they are ingested from the boundary layer due to either convective transport or orographic lift.

The accomplishments in addressing Objective 2 include the following:

  • Validation of the satellite inferences of cloud microstructure using the in-cloud measurements from the cloud physics aircraft on two days of measurement (February 7 and March 4, 2005).

  • Verification that pollution aerosols are instrumental in altering the internal structure of the clouds and their resultant precipitation.

    The use of the cloud physics aircraft has made possible the documentation of dramatic differences in cloud microstructure associated with differences in CCN, measured by the airborne CCN counter that were visibly related to air pollution. It was determined further that these differences were related to the satellite retrievals, which were validated by the aircraft measurements. Pollution is certainly affecting Sierra clouds and precipitation detrimentally. Through the aircraft and satellite measurements in SUPRECIP it has been noted that much of the Sierra precipitation was produced by surprisingly shallow pristine clouds. This suggests that pollution will act detrimentally on such clouds and may help explain the long-term losses in Sierra orographic precipitation.


Copyright © 2005