A Comparison of CAM5/CARMA Tropical Tropopause Layer Cirrus Cloud Simulations with ATTREX 3 and Satellite Observations

Cirrus clouds in the TTL have been observed to impact the dehydration of air transported from the upper troposphere to the lower stratosphere as well as influence Earth’s radiation budget. As a result, improving the ability of global climate models to properly represent high cirrus clouds in the Tropical Tropopause Layer (TTL) is important to furthering our ability to properly characterize climate in model simulations. Here we present work using three separate observational platforms to assess the treatment of high cirrus clouds in the NSF/DOE Community Earth System Model’s atmospheric model, CAM5, coupled with a sectional microphysics model, CARMA. For a more direct comparison with satellite observations, the CFMIP Observations Suite Package (COSP) is utilized. The COSP simulator package reproduces satellite observations by mimicking satellite retrieval algorithms within the model. The three observational data sets used in this study are a set of in-situ aircraft observations from the ATTREX 3 field mission which occurred over the Western Pacific in early 2014, and the long running CALIPSO and MODIS satellite observations. Based on initial comparisons between simulations and data we have made a number of model adjustments to better represent water vapor and thin cirrus clouds near the tropical tropopause. The results from our model improvements and comparisons with observations are presented here.