Evaluation of the Cloud Characteristics in NCAR CAM model over the Southern Ocean and the Arctic Region

Clouds play a crucial role in modifying the Earth's radiation budget. Using observations to validate global climate model simulations over the higher latitudinal regions is important for improving model parameterizations. In this work, an evaluation of the NCAR Community Atmospheric Model version 5 and 6 (CAM5 and CAM6) is conducted by comparing with an in-situ airborne observation over the Southern Ocean and Arctic. The in-situ observations are obtained from the NSF Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) campaign, and the NSF HIAPER Pole-to-Pole (HIPPO) Global campaign.Our evaluation targets cloud characteristics at -40°C - 0°C for the coexistence of supercooled liquid water and ice particles.

There are two typical conditions when clouds containing supercooled liquid water (SLW) are misrepresented in the CAM model, that is, either the model misses the SLW completely, or misrepresents the cloud phase that the SLW is embedded in. Overall, CAM6 has shown an improvement of simulating mixed phase clouds in the temperature range from -40°C to -20°C compared with CAM5. For warmer temperature range from -15°C to 0°C, CAM6 underestimates the frequency of mixed phase segments but overestimates the frequency of liquid phase. By considering snow as part of the ice water content, however, highly increases the occurrence frequency of mixed phase at -15°C - 0°C, resulting in overestimation of mixed phase frequency in CAM6. Our results will highlight the importance of using similar definitions of in-cloud quantities for comparisons between observations and simulations.