HR: 0800h
AN: A31A-0011    [Abstracts]
TI: Low Cloud Climate Feedback Mechanisms in Idealized Simulations with the Community Atmospheric Model (CAM3)
AU: * Zhang, M
EM: mzhang@notes.cc.sunysb.edu
AF: ITPA, Stony Brook University, Stony Brook, NY 11794,
AU: Bretherton, C
EM: breth@washington.edu
AF: Depart of Atmospheric Sciences, University of Washington, Seattle, WA 351640,
AB: This study investigates the physical mechanism of low cloud feedback in the Community Atmospheric Model (CAM3) through idealized experiments over the subtropical eastern oceans. Negative cloud feedback is simulated from stratus and stratocumulus that is consistent with previous diagnostics of cloud feedbacks in CAM3 and its predecessor versions. The negative feedback is attributed to the increased lower-level convective instability due to the Clausius-Clapeyron dependence of surface moisture on temperature, and the relatively small sensitivity of cloud water to temperature than rain production. The former is responsible for the larger amount of in-cloud water in stratiform clouds, while the latter is responsible for a longer life time of clouds, both of which contributed to the negative cloud feedback. The feedback is materialized through the interaction of a suite of parameterized processes rather than from any single process. These include convection, boundary layer turbulence, radiation, cloud fraction, and the cloud macrophysical and microphysical schemes. The thermodynamic effect is found to dominate the negative cloud feedback in the model. The dynamic effect of weaker subsidence in a warmer climate also contributes to the negative cloud feedback, but with about one quarter of the magnitude of the thermodynamic effect.
DE: 3310 Clouds and cloud feedbacks
DE: 3314 Convective processes
DE: 3337 Global climate models (1626, 4928)
DE: 3374 Tropical meteorology
DE: 3379 Turbulence (4490)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting