CGILS: Results from the first phase of an international project to understand the physical mechanisms of low cloud feedbacks in single column modelsReport as inadecuate




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1 SUNY Stony Brook, Inst Terr & Planetary Atmospheres, Sch Marine & Atmospher Sci, Stony Brook, NY 11794 USA 2 Univ Washington, Dept Atmospher Sci, Seattle, WA 98195 USA 3 Univ British Columbia, Dept Earth & Ocean Sci, Vancouver, BC V5Z 1M9, Canada 4 Natl Ctr Atmospher Res, Earth Syst Lab, Boulder, CO 80307 USA 5 LMD - Laboratoire de Météorologie Dynamique 6 MPI-M - Max-Planck-Institut für Meteorologie 7 NASA, Goddard Inst Space Studies, New York, NY 10025 USA 8 Delft Univ Technol, Dept Geosci & Remote Sensing, Delft, Netherlands 9 Brookhaven Natl Lab, Dept Environm Sci, Upton, NY 11973 USA 10 NOAA, Geophys Fluid Dynam Lab, Princeton, NJ USA 11 ETH Zürich - Swiss Federal Institute of Technology in Zürich 12 CSIRO, Ctr Australian Weather & Climate Res, Aspendale, Vic, Australia 13 LaRC - NASA Langley Research Center Hampton 14 Seoul Natl Univ, Sch Earth & Environm Sci, Seoul, South Korea 15 Meteorol Res Inst, Tsukuba, Ibaraki 305, Japan 16 ECMWF - European Centre for Medium-Range Weather Forecasts 17 Met Off Hadley Ctr, Exeter, Devon, England 18 NASA, Global Modeling & Assimilat Off, Goddard Space Flight Ctr, Greenbelt, MD USA 19 KNMI - Royal Netherlands Meteorological Institute 20 Pacific NW Natl Lab, Richland, WA 99352 USA 21 Univ Wisconsin, Dept Math Sci, Milwaukee, WI 53201 USA 22 Columbia Univ, Goddard Inst Space Studies, New York, NY USA 23 Canadian Ctr Climate Modelling & Anal, Victoria, BC, Canada

Abstract : CGILS-the CFMIP-GASS Intercomparison of Large Eddy Models LESs and single column models SCMs-investigates the mechanisms of cloud feedback in SCMs and LESs under idealized climate change perturbation. This paper describes the CGILS results from 15 SCMs and 8 LES models. Three cloud regimes over the subtropical oceans are studied: shallow cumulus, cumulus under stratocumulus, and well-mixed coastal stratus-stratocumulus. In the stratocumulus and coastal stratus regimes, SCMs without activated shallow convection generally simulated negative cloud feedbacks, while models with active shallow convection generally simulated positive cloud feedbacks. In the shallow cumulus alone regime, this relationship is less clear, likely due to the changes in cloud depth, lateral mixing, and precipitation or a combination of them. The majority of LES models simulated negative cloud feedback in the well-mixed coastal stratus-stratocumulus regime, and positive feedback in the shallow cumulus and stratocumulus regime. A general framework is provided to interpret SCM results: in a warmer climate, the moistening rate of the cloudy layer associated with the surface-based turbulence parameterization is enhanced; together with weaker large-scale subsidence, it causes negative cloud feedback. In contrast, in the warmer climate, the drying rate associated with the shallow convection scheme is enhanced. This causes positive cloud feedback. These mechanisms are summarized as the -NESTS- negative cloud feedback and the -SCOPE- positive cloud feedback Negative feedback from Surface Turbulence under weaker Subsidence-Shallow Convection PositivE feedback with the net cloud feedback depending on how the two opposing effects counteract each other. The LES results are consistent with these interpretations.





Author: Minghua Zhang - Peter N. Blossey - Marat F. Khairoutdinov - Phillip H. Austin - Julio T. Bacmeister - Sandrine Bony - Florent Bri

Source: https://hal.archives-ouvertes.fr/



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