CGILS: Results from the first phase of an international project to understand the physical mechanisms of low cloud feedbacks in single column models
M. Zhang; Bretherton, C. S.; Blossey, P. N.; Austin, P. H.; Bacmeister, J. T.; Bony, S.; Brient, F.; Cheedela, S. K.; Cheng, A.; Del Genio, A. D.; de Roode, S. R.; Endo, S.; Franklin, C. N.; Golaz, J. C. and others – 2013
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 = {Zhang, M. and Bretherton, C.~S. and Blossey, P.~N. and Austin, P.~H. and Bacmeister, J.~T. and Bony, S. and Brient, F. and Cheedela, S.~K. and Cheng, A. and {Del Genio}, A.~D. and {de Roode}, S.~R. and Endo, S. and Franklin, C.~N. and Golaz, J.~C. and Hannay, C. and Heus, T. and Isotta, F.~A. and Dufresne, J.~L. and Kang, I.~S. and Kawai, H. and Köhler, M. and Larson, V.~E. and Liu, Y. and Lock, A.~P. and Lohmann, U. and Khairoutdinov, M.~F. and Molod, A.~M. and Neggers, R.~A.~J. and Rasch, P. and Sandu, I. and Senkbeil, R. and Siebesma, A.~P. and {Siegenthaler-Le Drian}, C. and Stevens, B. and Suarez, M.~J. and Xu, K.~M. and {von Salzen}, K. and Webb, M.~J. and Wolf, A. and Zhao, M.},
title = {CGILS: Results from the first phase of an international project to understand the physical mechanisms of low cloud feedbacks in single column models},
journal = {Journal of Advances in Modeling Earth Systems},
volume = {5},
number = {4},
pages = {826-842},
year = {2013}
}