Clouds and Convection in Extra-Tropical Cyclones over the Southern Ocean in GFDL AM4
Abstract
Climate-model biases in shortwave absorption over the Southern Ocean have been attributed to deficiencies in the simulation of clouds in the cold sectors of extra-tropical cyclones. We composite cloud patterns in GFDL AM4's Southern Hemisphere extra-tropical cyclones and evaluate these patterns against MODIS, Cloudsat, and CALIPSO observations. We find that the dynamics and moisture fields are realistically simulated for the extra-tropical cyclones, as are qualitative relationships among clouds and frontal positions, including large differences detected by Cloudsat and CALIPSO between the vertical extent of clouds in the warm and cold sectors related to warm-front conveyor belts.
Although most of the modeled clouds in the extra-tropical cyclones are stratiform in character, we find differences in both stratiform and convective clouds in all sectors of the extra-tropical cyclones related to the choice of cumulus parameterization. In particular, a variant of AM4 in which multiple plumes are introduced for deep convection with their entrainment rates constrained by observed updraft vertical velocities produces more clouds behind cold fronts when parameters are optimized for global energy balance. These changes in extra-tropical clouds with cumulus parameterization are related to differences in parameterization structure, especially treatment of entrainment, and model tuning.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A13B..07D
- Keywords:
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- 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0321 Cloud/radiation interaction;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3349 Polar meteorology;
- ATMOSPHERIC PROCESSES