The Indirect and Semi-Direct Aerosol Campaign (ISDAC): Examining the Influences of Arctic Aerosols on Clouds

Aerosols influence clouds through a variety of mechanisms. Nowhere is this influence more complex than in the Arctic. The Indirect and Semi-Direct Aerosol Campaign (ISDAC), sponsored by the Department of Energy Atmospheric Radiation Measurement (ARM) program, was conducted over Barrow in April 2008 to directly address this complexity. The National Research Council (NRC) of Canada Convair-580 flew a total of 27 sorties during ISDAC, collecting data from 42 cloud and aerosol instruments for more than 100 hours on 12 different days. Several additional instruments were operated at the North Slope of Alaska Barrow facility throughout the campaign. This unprecedented set of in-situ and remote sensing measurements sampled a wide range of aerosol conditions during ISDAC. Data obtained above, below and within single-layer stratus during two golden cases on April 8 and April 26 2008 are allowing for a process-oriented understanding of how cloud-aerosol interactions affects the microphysical and radiative properties of arctic clouds in different surface and aerosol conditions. Data acquired on a heavily polluted day on April 19 are also being used to enhance this understanding.

This presentation will show how the ISDAC data are being used to address the following primary science questions: 1) how do the properties of arctic aerosol during April differ from those measured in October 2004 during the Mixed-Phase Arctic Cloud Experiment?; 2) to what extent do different properties of arctic aerosol produce differences in microphysical and macrophysical properties of clouds and the surface energy balance?; 3) how well can cloud models and parameterizations in large-scale models simulate the sensitivity of arctic clouds and the surface energy budget to differences in aerosol properties?; and 4) how well can long-term surface-based measurements at the ACRF Barrow site provide retrievals of aerosols, clouds, precipitation and radiative heating in the Arctic? The ISDAC data are also being used to examine the composition of ice nuclei and to determine the extent to which shattering of large crystals on protruding components of probes artificially amplifies the measured concentrations of ice crystals with maximum dimensions < 50 micrometers.