Ice and Supercooled Liquid Distributions Based on in Situ Observations and Climate Model Simulations

Abstract

Three climate models are evaluated using in situ airborne observations from the SouthernOcean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) campaign. The evaluation targets cloud phases, microphysical properties, thermodynamic conditions, and aerosol indirect effects from -40°C to 0°C. Compared with 580-s averaged observations (i.e., 100 km horizontal scale), the Community Atmosphere Model version 6 (CAM6) shows the most similar result for cloud phase frequency distribution and allows more liquidcontaining clouds below -10°C compared with its predecessor—CAM5. The Energy Exascale Earth System Model (E3SM) underestimates (overestimates) ice phase frequencies below (above) -20°C. CAM6 and E3SM show liquid and ice water contents (i.e., LWC and IWC) similar to observations from -25°C to 0°C, but higher LWC and lower IWC than observations at lower temperatures. Simulated in-cloud RH shows higher minimum values than observations, possibly restricting ice growth during sedimentation. As number concentrations of aerosols larger than 500 nm (Na500) increase, observations show increases of liquid and ice. Number concentrations of aerosols larger than 100 nm (Na100) only show positive correlations with liquid. CAM6 shows small increases of liquid with Na500 and Na100. E3SM shows small increases of. Overall, CAM6 and E3SM underestimate aerosol indirect effects on ice crystals and supercooled liquid droplets over the Southern Ocean.