Testing Climate Model Simulations of Cloud Lifecycle Dynamics
Using NASA A-Train Measurements

PI: Brian J. Soden

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.

This project combines 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 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 project are:

• (i) Develop supplementary products to quantify the Lagrangian properties of tropical cloud sys¬tems observed by the NASA A-Train; e.g., their origin, lifetime, trajectories, etc.
• (ii) Through compositing techniques, characterize the Lagrangian evolution of tropical cloud systems in terms of their radiative and microphysical properties retrieved from NASA A-Train instruments.
• (iii) Analyze the dependence of cirrus anvil properties and upper tropospheric humidity on the char¬acteristics of the convective sources which generate them;
• (iv) Quantify the impact of cirrus detrainment on the moisture budget and humidification of the upper troposphere following a convective event.
• (v) Test the representation of convective-cirrus-humidity lifecycle processes in different versions of the GFDL and NCAR GCMs which are known to have widely varying strengths of high cloud feedbacks.

This project will focus primarily on the analysis of Level 2 retrieved products from the following instruments:

• radiative fluxes from CERES
• cloud property retrievals from CloudSat, CALIPSO, and MODIS
• humidity profiles from AIRS, AMSU, and GOES/GMS/METEOSAT
• precipitation measurements from AMSR-E

GOES, GMS and METEOSAT imagery will be used to construct forward and back trajectories for the cloud systems observed the NASA A-Train satellites. By co-locating the geostationary satellites with the flight swaths from the individual instruments, the Lagrangian history of the particular cloud systems that were observed can be reconstructed and used to address the key questions outlined above. By combining satellite measurements in a format directly tailored for evalu¬ating model simulations, this proposal seeks to enhance our understanding of tropical convection, cirrus clouds and upper tropospheric water vapor and, in so doing, contribute to NASA’s long-term objective of reducing uncertainty in cloud feedbacks.