Development and evaluation of convective cloud microphysics parameterization in the NCAR CAM5
Authors
Guang Zhang — University of California, San Diego
Xiaoliang Song — Scripps Institution of Oceanography
Category
Modeling
Description
Vertical profiles of cloud IWC (g m-3) in convection core during active monsoon period (19¬–25 January, 2006) of ARM TWP-ICE from (a) satellite, (b) SCM control run (CTL), and (c) SCM experiment including convective microphysics (MPHY), and vertical profiles of cloud LWC (g m-3) from (d) C-POL radar, (e) CTL, and (f) MPHY.
A two-moment microphysics parameterization scheme for convective clouds is developed to improve the representation of convective clouds and their interactions with stratiform clouds and aerosol in GCMs. The scheme explicitly treats mass mixing ratio and number concentration of four hydrometeor species (cloud water, cloud ice, rain, and snow) and describes several microphysical processes, including autoconversion, self-collection, collection between hydrometeor species, freezing, cloud ice nucleation, droplet activation, and sedimentation. This physically based scheme is suitable for investigating the interaction between convection and aerosol and the indirect aerosol effect on climate. An evaluation of the scheme in the single-column version of NCAR Community Atmospheric Model version 3.5 (CAM3.5) with the Tropical Warm Pool-International Cloud Experiment (TWP-ICE) data shows that the simulation of cloud microphysical properties in convective core is significantly improved, indicating that the new parameterization describes the microphysical processes in convection reasonably well. The contribution from convective detrainment to large-scale cloud ice and liquid water budgets is enhanced greatly. With more realistic convective cloud microphysical properties and their detrainment, the surface stratiform precipitation is increased. The scheme is implemented into CAM5 for further tests. Comparison with CloudSat observations of convective cloud ice water content draws similar conclusions on a global scale to those from single-column model simulation. The global simulation of clouds and hydrological cycle in CAM5 shows increased low- and middle-level cloud fraction and large-scale precipitation in the tropics.
