Predicting Frigid Mixed‐Phase Clouds for Pristine Coastal Antarctica.

Supercooled water is common in the clouds near coastal Antarctica and occasionally occurs at temperatures at or below −30°C. Yet the ice physics in most regional and global numerical models will glaciate out these clouds. This presents a challenge for the simulation of highly supercooled clouds that were observed at McMurdo, Antarctica during the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE) project during 2015–2017. The polar optimized version of the Weather Research and Forecasting model (Polar WRF) with the recently developed two‐moment P3 microphysics scheme was used to simulate observed supercooled liquid water cases during March and November 2016. Nudging of the simulations to observed rawinsonde profiles and Antarctic automatic weather station observations provided increased realism and much greater cloud water amounts. Sensitivity tests that adjust the ice physics for extremely low ice nucleating particle (INP) concentrations decrease cloud ice and increases the cloud liquid water closer to observed amounts. In these tests, a liquid layer near cloud top is simulated, in agreement with observations. Accurate representation of INP concentrations appears to be critical for the simulation of coastal Antarctic clouds. Plain Language Summary: Liquid water is common in the clouds observed at McMurdo Station located on Ross Island, Antarctica. The liquid water occurs even when the temperature is well below freezing and ice might be expected from the common physics of clouds. The pristine atmosphere there has very few particles that are favorable for the formation of cloud ice. Models with cloud physics set for more populated regions of Earth therefore have difficulty simulating these cold liquid clouds. When we adjust our regional model Polar WRF for the pristine conditions, it improves the simulation of the liquid clouds. Also, our simulations can underrepresent the amount of water substance in vapor form in the coastal Antarctic atmosphere. This error appears to arise from the dry external forcing source we use for the regional simulations. When we adjust the simulations by gradually nudging toward balloon‐based observations at McMurdo and other regional observations the amount of vapor increases toward observed values. This has the beneficial result of improving the simulation of clouds. We believe that atmospheric models need to better represent the particulates in the atmosphere to improve the cloud simulations near Antarctica and elsewhere. Key Points: Data assimilation increases the modeled water vapor closer to observed amounts and improves Antarctic clouds in mesoscale simulationsAdding realistic ice nucleating particle (INP) concentrations in models improves simulated clouds in better agreement with observationsHighly supercooled liquid water extending to cloud tops observed at McMurdo can properly be simulated by specifying sparse amounts of INP [ABSTRACT FROM AUTHOR]