Double-moment cloud microphysics scheme for the deep convection parameterization in the GFDL AM3

Poster PDF

Description

A double-moment cloud microphysical scheme originally developed by Morrision and Gettelman (2008) for the stratiform clouds and later adopted for the deep convection by Song and Zhang (2011) is being implemented in to the Geophysical Fluid Dynamics Laboratory's atmospheric general circulation model AM3. The scheme treats cloud drop, cloud ice, rain, and snow number concentrations and mixing ratios as diagnostic variables and incorporates processes of autoconversion, self-collection, collection between hydrometeor species, sedimentation, ice nucleation, drop activation, homogeneous and heterogeneous freezing, and the Bergeron-Findeisen process. Such detailed representation of microphysical processes makes the scheme suitable for studying the interactions between aerosols and convection, as well as aerosols' indirect effects on clouds and their roles in climate change.

As the first step of implementation, the scheme is tested in the single column version of the GFDL AM3 using forcing data obtained at the U.S. Department of Energy Atmospheric Radiation Measurement Climate Research Facility's Southern Great Plains and Tropical Western Pacific sites. In the future, tests with the full atmospheric GCM will be conducted. In addition, sensitivity of the scheme to the parameterizations of some collection processes that were originally obtained for the stratiform cloudiness regime will be investigated. Specifically, these are formulations for autoconversion of cloud water and its accretion by rain as well as the formulation for self-collection of rain and self-collection of snow.

Morrison, H, and A Gettelman. 2008. “A new two-moment bulk stratiform cloud microphysics scheme in the Community Atmosphere Model, version 3 (CAM3). Part I: Description and numerical tests.” Journal of Climate 21: 3642–3659.

Song, X, and GJ Zhang. 2011. “Microphysics parameterization for convective clouds in a global climate model: Description and single-column model tests.” Journal of Geophysical Research 116: D02201, doi:10.1029/2010JD014833.