Toward ice formation closure in Arctic mixed-phase boundary layer clouds during ISDAC

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DOIResolve DOI: http://doi.org/10.1029/2011JD015910
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TypeArticle
Journal titleJournal of Geophysical Research D: Atmospheres
ISSN0148-0227
Volume116
Issue19
Article numberD00T08
SubjectBoundary layer clouds; Cloud layers; Doppler velocity; High density; Ice concentration; Ice formations; Ice nuclei; Ice particles; Ice size distribution; Low density; Microphysical process; Microphysics; Mixed-phase cloud; Modeling studies; Number concentration; Parameterizations; Radar reflectivities; Water saturations; Agglomeration; Clouds; Computer simulation; Reservoirs (water); Uncertainty analysis; Ice; aerosol; boundary layer; Doppler effect; eddy; heterogeneity; ice; measurement method; numerical model; radar; uncertainty analysis; Arctic
AbstractA modeling study of a low-lying mixed-phase cloud layer observed on 8 April 2008 during the Indirect and Semi-Direct Aerosol Campaign is presented. Large-eddy simulations with size-resolved microphysics were used to test the hypothesis that heterogeneous ice nucleus (IN) concentrations measured above cloud top can account for observed ice concentrations, while also matching ice size distributions, radar reflectivities, and mean Doppler velocities. The conditions for the case are favorable for the hypothesis: springtime IN concentrations are high in the Arctic, the predominant ice habit falls slowly, and overlying IN concentrations were greater than ice particle number concentrations. Based on particle imagery, we considered two dendrite types, broad armed (high density) and stellar (low density), in addition to high and low density aggregates. Two simulations with low-density aggregates reproduced observations best overall: one in which IN concentrations aloft were increased fourfold (as could have been present above water saturation) and another in which initial IN concentrations were vertically uniform. A key aspect of the latter was an IN reservoir under the well-mixed cloud layer: as the simulations progressed, the reservoir IN slowly mixed upward, helping to maintain ice concentrations close to those observed. Given the uncertainties of the measurements and parameterizations of the microphysical processes embedded in the model, we found agreement between simulated and measured ice number concentrations in most of the simulations, in contrast with previous modeling studies of Arctic mixed-phase clouds, which typically show a large discrepancy when IN are treated prognostically and constrained by measurements. Copyright 2011 by the American Geophysical Union.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21271744
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Record identifierbb7c6e1d-597a-4621-af54-13c25bfad9b4
Record created2014-03-24
Record modified2016-05-09
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