Evaluating Aerosol-Cloud and Cloud-Radiation interaction-simulations with a Single Column Model (SCM) using McRAS cloud physics with ARM data and satellite retrievals

Inclusions of aerosol-cloud radiation interactions are crucial for simulating realistic cloud radiative forcing in response to changes in aerosols. However, the parameterizations involved in linking aerosols with cloud microphysics are complex. We use the Fountoukis/Nenes aerosol activation for Cloud Condensation Nuclei (CCN), and the Liu/Penner and Barahona/Nenes schemes for cloud Ice Nucleation (IN) in the Microphysics of clouds with the Relaxed Arakawa–Schubert scheme (McRAS). These are coupled with the Chou/Suarez radiation algorithm in the GEOS4 GCM in its Single Column Model (SCM) incarnation. ARM Southern Great Plains (ARM-SGP) forcing data are used to drive the SCM while ground-based observations as well as satellite retrievals of MODIS of cloud optical properties data are used to evaluate the simulation. Whereas the SCM simulates realistic liquid clouds and associated optical properties, 20-40% biases in the ice clouds are found. The Liu/Penner parameterization produces relatively thinner clouds compared to Barahona/Nenes, which agrees with the ARM in-situ observations better. The observations indicate winter (summer) ice cloud optical thicknesses of 10 (20), whereas the corresponding simulated values are 3 (14) for Liu/Penner and 13 (32) for Barahona/Nenes. We will explore the cause of this discrepancy and present our findings in the meeting.