The dependence of arctic mixed-phase stratus ice cloud microphysics on aerosol concentration using observations acquired during ISDAC

 
Poster PDF

Authors

Greg McFarquhar — University of Oklahoma
Robert Jackson — Argonne National Laboratory
Alexei Korolev — Environment Canada
Michael Earle — Environment Canada
Peter Liu — Environment Canada
Paul Lawson — SPEC, Inc.
Sarah D. Brooks — Texas A&M University
Mengistu Wolde — National Research Council
Alexander Laskin — Purdue University
Matt Freer — University of Illinois, Urbana

Category

Field Campaigns

Description

Data acquired by the National Research Council of Canada (NRC) Convair-580 equipped with cloud and aerosol probes during five sorties through single-layer arctic stratocumulus on 8, 18, and 26 April 2008 during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) were used to test three aerosol indirect effects hypothesized to act in mixed-phase clouds: the riming indirect effect, the glaciation indirect effect, and the cold second indirect effect. The data showed a correlation of R2 = 0.75 between liquid drop number concentration Nl inside cloud and ambient aerosol number concentration NPCASP below cloud. This, combined with an increase of liquid water content LWC with height above cloud base and the nearly constant profile of Nl, showed that liquid drops were likely nucleated from aerosol at cloud base. No strong evidence of a riming indirect effect was observed for the ISDAC single-layer stratus. A strong correlation of R2 = 0.69 between ice crystal number concentration Ni and NPCASP above cloud was noted for ISDAC. Increases in ice nuclei (IN) concentration with NPCASP above cloud combined with the subadiabatic LWC profiles suggest possible mixing of aerosol and IN from cloud top consistent with the glaciation indirect effect for ISDAC. The higher Ni and lower rel observed for the more polluted ISDAC cases compared to the cleaner M-PACE cases is consistent with the operation of the cold second indirect effect.