CESM cloud feedback: connections to the storm tracks and tropical circulation

Monday, 15 December 2014
Benjamin M Wagman and Charles S Jackson, University of Texas, Institute for Geophysics, Austin, TX, United States
Differences in the way that climate models simulate changes in low tropical clouds account for the majority of the inter-model spread in cloud feedback. However, the Community Earth System Model (CESM1) and its predecessors CCSM4 and CCSM3 show uncommon sensitivity to the shortwave cloud feedback in the storm tracks rather than the tropics. The storm track feedback is coupled to aspects of the meridional overturning circulation in both CESM and its predecessors, so these effects are somehow linked but the connection is poorly understood. In order to further explore the connection between climate sensitivity and circulation in CESM, an ensemble is being conducted using a slab ocean, perturbed atmospheric convection parameters, and the spectral element dycore. The ensemble is controlled by the Multiple Ensemble Control System (MECS), which stochastically samples the uncertainty in convection parameters using very fast simulated annealing (VFSA) to converge on an approximation of the posterior probability distribution of uncertain parameters.