Brian Soden (PI)
University of Miami
bsoden@rsmas.miami.edu

Testing Model Simulations of Cloud Lifecycles Using NASA A-Train Measurements

Understanding the processes which control the water budget of the tropical upper troposphere is essential for the successful modeling of the Earth’s climate. The feedbacks from upper tropospheric water vapor and cirrus represent some of the most important and most controversial within the climate system. Prediction of these feedback effects ultimately requires understanding the full lifecycle of tropical cloud systems and their impact on the moisture budget of the upper troposphere - from generation in deep convection to horizontal spreading and ultimate dissipation and conversion to vapor.   The basic premise of this proposal is that differences in cloud feedback between various versions the GFDL and NCAR global climate models are manifest in their contrasting cloud lifecycles. By integrating NASA A-Train retrievals with Lagrangian trajectories from geostationary satellites we intend to test and ultimately improve the representation of tropical cloud lifecycles in these models and, in so doing, reduce uncertainty in their simulations of cloud feedback.   The proposed research involves an innovative method of combining NASA A-train and geostationary satellite data to quantitatively describe the lifecycle of tropical cloud systems and their subsequent impacts on the radiative and moisture budgets of the upper troposphere. The resulting Lagrangian data set will then be used to test different versions of the new GFDL and NCAR models which have been shown to exhibit a wide range of climate sensitivities and cloud feedbacks. The primary tasks to be accomplished under this proposal are: (1) Develop Lagrangian-based products to compliment the more traditional Eulerian data streams by providing forward / backward trajectories and related Lagrangian diagnostics for cloud systems observed by the NASA A-Train satellites. (2) Use Lagrangian-based composites of NASA A-Train retrievals to characterize the radiative, macrophysical, and microphysical evolution of tropical cloud systems.  (3) Use the Lagrangian information to assess the dependence of the detrained cirrus cloud properties upon the characteristics of the convective sources which generate them. (4) Evaluate the ability of the GFDL and NCAR Global Climate Models (GCMs) to simulate the relevant physical processes governing the observed lifecycle of tropical convective systems and their impact on the moisture and radiation budgets.

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