Representing the competition between various ice formation processes in CAM5

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Thursday, 6 February 2014: 8:45 AM
Room C207 (The Georgia World Congress Center )
Kai Zhang, PNNL, Richland, WA; and X. Liu and H. Wan

Ice crystals form in the atmospheric mainly by freezing of super-cooled liquid water droplets with ice nuclei as a catalyst, and by homogeneous/heterogeneous freezing of certain types of aerosol particles. Because cloud droplets and aerosols freeze at different temperatures and supersaturation, certain ice formation processes can happen earlier and consequently prohibit the happening of other processes.

Newer generation global climate models, such as the Community Atmospheric Model version 5 (CAM5), have started to consider several ice formation mechanisms simultaneously, although the coupling between these processes has not been well addressed. In this work, we use the global aerosol-climate model CAM5 and its single column version (SCAM5) to investigate the impact of process coupling on the formation and development of cold clouds. We first carry out a convergence test and establish the reference solution. Different coupling methods are then evaluated by performing detailed ice water budget analysis. Results show that the simulated ice crystal concentrations and cloud forcing are sensitive to the coupling method and some empirical treatments applied in the model. We will also discuss possible ways to remove modeling artifacts and obtain robust simulations of ice clouds in the CAM5 model.