Aerosol Specification in Single-Column Community Atmosphere Model Version 5

TitleAerosol Specification in Single-Column Community Atmosphere Model Version 5
Publication TypeJournal Article
Year of Publication2015
JournalGeophysical Model Development
Volume8
Pages817-828
Date Published03/2015
Abstract / Summary

Single-column model (SCM) capability is an important tool for general circulation model development. In this study, the SCM mode of version 5 of the Community Atmosphere Model (CAM5) is shown to handle aerosol initialization and advection improperly, resulting in aerosol, cloud-droplet, and ice crystal concentrations which are typically much lower than observed or simulated by CAM5 in global mode. This deficiency has a major impact on stratiform cloud simulations but has little impact on convective case studies because aerosol is currently not used by CAM5 convective schemes and convective cases are typically longer in duration (so initialization is less important). By imposing fixed aerosol or cloud-droplet and crystal number concentrations, the aerosol issues described above can be avoided. Sensitivity studies using these idealizations suggest that the Meyers et al. (1992) ice nucleation scheme prevents mixed-phase cloud from existing by producing too many ice crystals. Microphysics is shown to strongly deplete cloud water in stratiform cases, indicating problems with sequential splitting in CAM5 and the need for careful interpretation of output from sequentially split climate models. Droplet concentration in the general circulation model (GCM) version of CAM5 is also shown to be far too low (~ 25 cm−3) at the southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site.

URLhttp://www.geosci-model-dev.net/8/817/2015/gmd-8-817-2015.html
DOI10.5194/gmd-8-817-2015
Journal: Geophysical Model Development
Year of Publication: 2015
Volume: 8
Pages: 817-828
Date Published: 03/2015

Single-column model (SCM) capability is an important tool for general circulation model development. In this study, the SCM mode of version 5 of the Community Atmosphere Model (CAM5) is shown to handle aerosol initialization and advection improperly, resulting in aerosol, cloud-droplet, and ice crystal concentrations which are typically much lower than observed or simulated by CAM5 in global mode. This deficiency has a major impact on stratiform cloud simulations but has little impact on convective case studies because aerosol is currently not used by CAM5 convective schemes and convective cases are typically longer in duration (so initialization is less important). By imposing fixed aerosol or cloud-droplet and crystal number concentrations, the aerosol issues described above can be avoided. Sensitivity studies using these idealizations suggest that the Meyers et al. (1992) ice nucleation scheme prevents mixed-phase cloud from existing by producing too many ice crystals. Microphysics is shown to strongly deplete cloud water in stratiform cases, indicating problems with sequential splitting in CAM5 and the need for careful interpretation of output from sequentially split climate models. Droplet concentration in the general circulation model (GCM) version of CAM5 is also shown to be far too low (~ 25 cm−3) at the southern Great Plains (SGP) Atmospheric Radiation Measurement (ARM) site.

DOI: 10.5194/gmd-8-817-2015
Citation:
Habtezion, BL, and PM Caldwell.  2015.  "Aerosol Specification in Single-Column Community Atmosphere Model Version 5."  Geophysical Model Development 8: 817-828.  https://doi.org/10.5194/gmd-8-817-2015.