Ice Nucleation in Mixed-phase Clouds: Parameterization Evaluation with the ISDAC Data and Climate Implication

Category: Aerosol-Cloud-Radiation Interactions

Working Group: Cloud-Aerosol-Precipitation Interaction

There are still large uncertainties about ice nucleation mechanisms and ice crystal numbers in mixed-phase clouds, which affect modeled cloud phase, cloud lifetime, and radiative properties in the Arctic clouds in global climate models. In this study we evaluate model simulations with three mixed-phase ice nucleation parameterizations (Phillips et al. 2008, DeMott et al. 2009, Meyers et al. 1992) against the Atmospheric Radiation Measurement (ARM) Indirect and Semi-Direct Aerosol Campaign (ISDAC) observations using the NCAR Community Atmospheric Model Version 4 (CAM4) running in the single- column mode (SCAM) and in the CCPP-ARM Parameterization Testbed (CAPT) forecasts. It is found that SCAM and CAPT, with the new physically based ice nucleation schemes (Phillips et al. 2008, DeMott et al. 2009), produce a more realistic simulation of the cloud phase structure and the partitioning of condensed water into liquid droplets against observations during the ISDAC than the CAM with an oversimplified Meyers et al. (1992). Both SCAM simulations and CAPT forecasts suggest that the ice number concentration could play an important role in the simulated mixed-phase cloud microphysics, and thereby needs to be realistically represented in global climate models. The global implication of different ice nucleation parameterizations also needs to be studied.

This poster will be displayed at ASR Science Team Meeting.

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