Testing ice microphysics parameterizations in the NCAR CommunityAtmospheric Model Version 3 using Tropical Warm Pool—International Cloud Experiment data

摘要

Cloud properties have been simulated with a new double-moment microphysicsscheme under the framework of the single-column version of NCAR CommunityAtmospheric Model version 3 (CAM3). For comparison, the same simulation was made with the standard single-moment microphysics scheme of CAM3. Results from bothsimulations compared favorably with observations during the Tropical WarmPool—International Cloud Experiment by the U.S. Department of Energy AtmosphericRadiation Measurement Program in terms of the temporal variation and verticaldistribution of cloud fraction and cloud condensate. Major differences between the twosimulations are in the magnitude and distribution of ice water content within themixed-phase cloud during the monsoon period, though the total frozen water (snow plusice) contents are similar. The ice mass content in the mixed-phase cloud from the newscheme is larger than that from the standard scheme, and ice water content extends 2 kmfurther downward, which is in better agreement with observations. The dependence of thefrozen water mass fraction on temperature from the new scheme is also in betteragreement with available observations. Outgoing longwave radiation (OLR) at the top ofthe atmosphere (TOA) from the simulation with the new scheme is, in general, larger thanthat with the standard scheme, while the surface downward longwave radiation issimilar. Sensitivity tests suggest that different treatments of the ice crystal effective radiuscontribute significantly to the difference in the calculations of TOA OLR, in addition tocloud water path. Numerical experiments show that cloud properties in the newscheme can respond reasonably to changes in the concentration of aerosols and emphasizethe importance of correctly simulating aerosol effects in climate models for aerosol-cloudinteractions. Further evaluation, especially for ice cloud properties based on in situdata, is needed.