Liquid and ice cloud microphysics in the CSU general circulation model. Part III: Sensitivity to modeling assumptions
- Colorado State Univ., Fort Collins, CO (United States)
Climate sensitivity, simulated by a general circulation model, to cloud microphysical process parameters and interactions with cumulus convection and radiative transfer parameters was investigated. Results of 120-day sensitivity experiments were compared with a control simulation. Results are presented in terms of 30-day mean differences. Advection of water species has little influence on geographic distributions and global averages. The simulated climate is unchanged when detrained condensed water at the tops of cumulus towers is a source of rain and snow rather than cloud water and ice. Instantaneously removing detrained cloud water and ice yields strong atmospheric drying and a significant reduction in anvil size. Altering partitioning between cloud ice and supercooled cloud water significantly changes vertical distributions of cloud optical depth and effective cloud fraction, producing significant variations in top-of-the-atmosphere longwave and shortwave cloud radiative forcings. Increasing fall speeds of rain and snow decreases cloudiness and increases stratiform rainfall. Increasing thresholds for autoconversion of cloud water to rain and cloud ice to snow significantly increases middle- and high-level clouds and reduces the cumulus precipitation rate. Collection of supercooled cloud water by snow appeared to be an important microphysical process for mixed-phase clouds. Optical effects of snow have little impact on top-of-the-atmosphere radiation budget. This study illustrates the need for in-depth analysis of spatial and temporal scale dependence of microphysical cloud parameters for general circulation models. 22 refs., 25 figs., 4 tabs.
- OSTI ID:
- 273949
- Journal Information:
- Journal of Climate, Vol. 9, Issue 3; Other Information: PBD: Mar 1996
- Country of Publication:
- United States
- Language:
- English
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