Participants can download idealized SCM/CRM/LES forcing data here (login id and passwd are the same as those at UW, NCAR, and GFDL).
Our next plan is to study the impact of the reduced subsidence on the variation of low clouds and their climate feedbacks. This will be carried out in two phases. One is to analyze the variation of subsidence rate and low clouds from different GCM simulations. The second is to use a single-column model with specified large-scale forcing and SST condition. In this second task, we will reduce the rate of subsidence and increase the SST to evaluate the response low clouds in the CAM SCM. Results will be compared with similar experiment from Min Zhao and Isaac Held at GFDL with the AM2 and from other CPT members.
This work has been carried out by Song Hua and Minghua Zhang under the NSF CPT collaborative grant to Stony Brook.
Detailed comparison of simulated clouds from the three models with satellite data, for each ISCCP cloud type, can be found here.
The second theme is to examine the variation of cloud types in climate change experiments, in particular what cloud types contribute the most to the model cloud feedbacks. We hope that results from the first theme on the comparison between model cloud types and ISCCP data can tell us what confidence we can put in the diagnosed cloud feedbacks in the models, and what cloud types need to be improved to improve the confidences.
Two climate change experiments have been carried out with the CAM, in which perturbations of SSTs from other coupled models are used as forcing. In both experiments, the model showed negative cloud feedback due to dominance of the reduction of shortwave cloud forcing. All experiments show increase of low cloud clouds, but decrease of high and middle clouds. The increase low cloud amount however is from the optically thick low clouds, while the decreased middle and high clouds are from the optically thin clouds. Results from these experiments can be found here.
Our next plan is to modify the CAM so that its basic cloud distributions, in particular the optically thick low clouds, become closer to ISCCP measurements, and then carry out similar climate change experiments to study the dependence of the cloud feedback on the model basic cloud climatology.
This work has been carried out by Wuyin Lin and Minghua Zhang
under the NSF CPT collaborative grant to Stony Brook .
Link to CPT at University Of Washington (with links to other CPT members)