Atmos. Chem. Phys. Discuss., 9, 12283-12344, 2009
www.atmos-chem-phys-discuss.net/9/12283/2009/
doi:10.5194/acpd-9-12283-2009
© Author(s) 2009. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Comparison of a global-climate model simulation to a cloud-system resolving model simulation for long-term thin stratocumulus clouds
S. S. Lee, J. E. Penner, and M. Wang
Department of Atmospheric, Oceanic, and Space Science, University of Michigan, Ann Arbor, MI, USA

Abstract. A case of thin, warm marine-boundary-layer (MBL) clouds is simulated by a cloud-system resolving model (CSRM) and is compared to the same case of clouds simulated by a general circulation model (GCM). In this study, the simulation by the CSRM adopts higher resolutions and more advanced microphysics as compared to those by the GCM, enabling the CSRM-simulation to act as a benchmark to assess the simulation by the GCM. Explicitly simulated interactions among the surface latent heat (LH) fluxes, buoyancy fluxes, and cloud-top entrainment lead to the deepening-warming decoupling and thereby the transition from stratiform clouds to cumulus clouds in the CSRM. However, in the simulation by the GCM, these interactions are not resolved and thus the transition to cumulus clouds is not simulated. This leads to substantial differences in cloud mass and radiation between simulations by the CSRM and the GCM. When stratocumulus clouds are dominant prior to the transition to cumulus clouds, interactions between supersaturation and cloud droplet number concentration (CDNC) (controlling condensation) and those between rain evaporation and cloud-base instability (controlling cloud dynamics and thereby condensation) determine cloud mass and thus the radiation budget in the simulation by the CSRM. These interactions result in smaller condensation and thus smaller cloud mass and reflected solar radiation by clouds in the simulation by the CSRM than in the simulation by the GCM where these interactions are not resolved. The resolved interactions (associated with condensation and the transition to cumulus clouds) lead to better agreement between the CSRM-simulation and observation than that between the GCM-simulation and observation.

Citation: Lee, S. S., Penner, J. E., and Wang, M.: Comparison of a global-climate model simulation to a cloud-system resolving model simulation for long-term thin stratocumulus clouds, Atmos. Chem. Phys. Discuss., 9, 12283-12344, doi:10.5194/acpd-9-12283-2009, 2009.
 
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