An Assessment of the Cirrus Cloud Representation in the Tropical Tropopause Layer of the CAM5/CARMA Model Through Comparisons With ATTREX 3 and CALIPSO Observations

Abstract:

Improving the ability of global climate models to properly represent high cirrus clouds is instrumental to furthering our ability to predict future climate. The extensive geographic coverage associated with high cirrus causes these clouds to have a strong impact on Earth’s radiation budget and the distribution of atmospheric water vapor. The influence on the radiation budget is greatest in the Tropical Tropopause Layer (TTL). Here we present work using two separate observational platforms to assess the treatment of high cirrus clouds in the NSF/DOE Community Earth System Model’s atmospheric model, CAM5. In this work CAM5 is coupled with a sectional microphysics model, CARMA. The CFMIP Observations Suite Package (COSP) utilized in our study mimics satellite retrieval algorithms and returns cloud products from the model that can be directly compared to satellite retrievals. The two observational data sets used in this comparison are a set of in situ observations from the ATTREX 3 field mission that took place over the Western Pacific in early 2014 and the long running CALIPSO observations. Based on these comparisons between simulations and data we have made a number of model adjustments to better represent water vapor and thin cirrus clouds near the tropopause. The results of those improvements are presented here.