A Unified Parameterization of Clouds and Turbulence using CLUBB and Subcolumns in the Community Atmosphere Model

TitleA Unified Parameterization of Clouds and Turbulence using CLUBB and Subcolumns in the Community Atmosphere Model
Publication TypeJournal Article
Year of Publication2015
JournalGeoscientific Model Development
Volume8
Pages3801-3821
Date Published12/2015
Abstract / Summary

Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.

URLhttp://www.geosci-model-dev.net/8/3801/2015/gmd-8-3801-2015.html
DOI10.5194/gmd-8-3801-2015
Journal: Geoscientific Model Development
Year of Publication: 2015
Volume: 8
Pages: 3801-3821
Date Published: 12/2015

Most global climate models parameterize separate cloud types using separate parameterizations. This approach has several disadvantages, including obscure interactions between parameterizations and inaccurate triggering of cumulus parameterizations. Alternatively, a unified cloud parameterization uses one equation set to represent all cloud types. Such cloud types include stratiform liquid and ice cloud, shallow convective cloud, and deep convective cloud. Vital to the success of a unified parameterization is a general interface between clouds and microphysics. One such interface involves drawing Monte Carlo samples of subgrid variability of temperature, water vapor, cloud liquid, and cloud ice, and feeding the sample points into a microphysics scheme. This study evaluates a unified cloud parameterization and a Monte Carlo microphysics interface that has been implemented in the Community Atmosphere Model (CAM) version 5.3. Model computational expense is estimated, and sensitivity to the number of subcolumns is investigated. Results describing the mean climate and tropical variability from global simulations are presented. The new model shows a degradation in precipitation skill but improvements in shortwave cloud forcing, liquid water path, long-wave cloud forcing, precipitable water, and tropical wave simulation.

DOI: 10.5194/gmd-8-3801-2015
Citation:
Thayer-Calder, K, A Gettelman, S Goldhaber, PA Bogenschutz, C Chen, H Morrison, J Höft, et al.  2015.  "A Unified Parameterization of Clouds and Turbulence using CLUBB and Subcolumns in the Community Atmosphere Model."  Geoscientific Model Development 8: 3801-3821.  https://doi.org/10.5194/gmd-8-3801-2015.