Global simulations of thin cirrus in the TTL with sectional ice microphysics

We use CAM/CARMA, a three-dimensional climate model based upon the latest version of the Community Atmosphere Model (CAM) General Circulation Model (GCM) with sectional microphysics from the Community Aerosol and Radiation Model for Atmospheres (CARMA) to investigate the importance of thin cirrus clouds in the Tropical Tropopause Layer (TTL). The new Morrison-Gettelman (MG) two-moment microphysics parameterization is used for liquid clouds, which allows for supersaturation with respect to ice within the model; however, the MG ice microphysics is replaced with a bin model based upon CARMA that separately tracks size distributions for both detrained and in-situ ice particles. Using simulations with an increased vertical resolution of ~300 m in the TTL, we explore the ability of the model to reproduce the geospatial distribution of clouds, temperature and water observed by several satellite instruments, including CloudSat, the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite (CALIPSO), the Constellation Observing System for Meteorology Ionosphere & Climate (COSMIC), the Microwave Limb Sounder (MLS) and the Atmospheric Infrared Sounder (AIRS). The sensitivity of the model to changes in the convective and microphysical parameterizations is also studied.