Towards Ice Formation Closure in Mixed-phase Boundary Layer Clouds During ISDAC

Alexander Avramov Columbia University
Andrew Ackerman NASA - Goddard Institute for Space Studies
Ann Fridlind NASA - Goddard Institute for Space Studies
Alexei Korolev Environment Canada
Sarah Brooks Texas A&M University
Andrew Glen Texas A&M University

Category: Modeling

Working Group: Cloud-Aerosol-Precipitation Interaction

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Level 1 (1 km at nadir) radiances in MODIS band 20 (3.7 um) during flight 16 with flight track and coastline overlaid respectively in black and white.

Mixed-phase stratus clouds are commonly found during winter and transition seasons in the Arctic and through various feedback mechanisms exert a strong influence on Arctic climate. Despite their important role, however, they are still difficult to represent correctly in cloud models. In particular, models of all types experience difficulties reproducing observed ice concentrations and liquid-ice water partitioning in these clouds. Previous modeling studies of arctic mixed-phase clouds have shown that simulated ice concentrations and ice water content are very sensitive to ice nucleation modes and ice crystal habit assumed in simulations. Here we use large-eddy simulations with size-resolved microphysics to determine whether uncertainties in ice nucleus concentrations, ice nucleation mechanisms, ice crystal habits, and large-scale forcing are sufficient to account for the difference between simulated and observed quantities. We focus on a case study from the Indirect and Semi-Direct Aerosol Campaign (ISDAC)—April 8, 2008 (Flight 16)—in which the full suite of instrumentation on the Convair-580 was operational (including the Nevzorov probe, which measures ice water content) and during which the aircraft overflew the Barrow ground site. We present analysis of the consistencies (and lack thereof) between the measurements and an extensive comparison of model results with the in situ observations and remote sensing measurements.

http://acrf-campaign.arm.gov/isdac/

This poster will be displayed at ASR Science Team Meeting.

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