Gerald Potter (PI)
Lawrence Livermore National Laboratory
gpotter@llnl.gov

Use of Satellite Data to Assess Tropical Clouds in Climate Models

The varying representation of clouds in climate models leads to varying predictions of the nature and magnitude of climate change. Clouds and the associated convection over the tropical ocean can play a large role in determining the sensitivity of climate. In this project, we plan to use both recent and future satellite datasets to assess the nature of tropical clouds in several climate models when run in a forecast mode. This bypasses the need to acquire very long records to assess climatological characteristics. At the Program for Climate Model Diagnosis and Intercomparison (PCMDI), the DOE sponsored Climate Change Prediction Program (CCPP) and the Atmospheric Radiation Measurements (ARM) have combined resources to create the CCPP-ARM Parameterization Testbed (CAPT) to facilitate climate model parameterization testing in a weather forecast mode. The CAPT project is running the NCAR Community Atmosphere Model version 3 (CAM3) and is adding the capability to run the GFDL AM2 model as well as prospectively the NASA GISS Model E.   We plan to focus on two related studies. The first will focus on the characteristics of the clouds, precipitation, and radiative forcing associated with the 1997/98 El Nino using satellite data from several platforms including CERES, TRMM, and SAGE. Climate models have trouble simulating the response of circulation, convection, and clouds to the anomalous sea-surface temperature in the tropical Pacific for this unusual period. Of interest is whether these same models will have difficulty simulating the response of convection and clouds when they are give the observed atmospheric state as initial conditions for forecasts.   In the second focus, we will examine the vertical characteristics of tropical clouds using data from CloudSat and humidity structures from AIRS and compare that to those simulated by climate models when run in forecast model. Previous work has demonstrated rather large differences between the NCAR CAM3 and GFDL AM2 vertical distributions of cloud fraction and condensate; contrasting these models’ cloud representation with the satellite observations will presumably highlight deficiencies in the heights of tropical anvils associated with convection and implications for the detrainment levels of deep convection. A period of particular interest will be the upcoming DOE/NASA sponsored Tropical Warm Pool – International Cloud Experiment to be held at Darwin, Australia in January 2006.

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