Impacts of Aerosols on Arctic Mixed-Phase Boundary Clouds During M-PACE and ISDAC Field Campaigns: Implications for Modelling Studies
Comprehensive data on arctic boundary layer aerosol and cloud microphysical and radiative properties were collected during the 2004 Mixed-Phase Arctic Cloud Experiment (M-PACE) and the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC). During M-PACE, the University of North Dakota Citation executed spiral ascents and descents through 27 mixed-phase clouds on 7 separate days over ground-based remote sensing sites at Barrow and Oliktok Point, Alaska. Data from in-situ microphysical sensors have been used to characterize how cloud particle shape, size, phase and bulk properties vary with height. These data have been used extensively to evaluate models that have contributed to our fundamental understanding of microphysical processes in mixed-phase clouds and produced potential explanations about the role of aerosols on observed ice nuclei concentrations.
However, M-PACE data were insufficient to evaluate all model hypotheses on causes of mixed-phase cloud persistence due to uncertainties in the microphysical data, the lack of information on aerosol composition and radiative properties, and the limited range of aerosol, surface and meteorological conditions over which data were obtained. ISDAC overcame these limitations and allows for an examination of the influence of aerosols on clouds influenced by ice. During ISDAC, the National Research Council of Canada Convair-580 flew 27 sorties, collecting data with an unprecedented 42 cloud and aerosol instruments for more than 100 hours on 12 different days. Data obtained above, below and within single-layer stratus during three separate days are allowing for a process-oriented understanding of how aerosols affect the microphysical and radiative properties of arctic clouds. Ultimately these data will be used to improve the representation of cloud and aerosol process in models covering a variety of spatial and temporal scales, and to determine the extent to which long-term surface-based measurements at a ground site at the North Slope of Alaska can provide retrievals of aerosols, clouds, precipitation and radiative heating in the Arctic. The need for future measurement campaigns in the Arctic to enhance the range of conditions sampled will also be discussed.