Evaluation of simulated cloud phase in EAMv2 at high latitudes
Liu, Xiaohong — Texas A&M University
Area of research
General Circulation and Single Column Models/Parameterizations
Mixed-phase clouds, in which liquid droplets and ice particles coexist at temperatures between 0 C and −40 C, play an essential role in modulating the surface energy budget and impacting future climate change. In this study, researchers used a satellite simulator to consistently evaluate model-simulated high-latitude clouds in the first and second versions of the Energy Exascale Earth System Model atmosphere model (EAMv1 and EAMv2) with satellite observations. They found that the modification of the Wegner-Bergeron-Findeisen (WBF) process is mainly responsible for the increased ice clouds in the central Arctic in EAMv2, improving the model agreements with observations. The new deep convective trigger in EAMv2 contributes to the better cloud phase over the Norwegian Sea and Barents Sea in the Arctic and the Southern Ocean, where large errors are found in EAMv1. However, the overestimation of supercooled liquid clouds near the surface in both hemispheres, and the underestimation of ice clouds over Antarctica in EAMv1, persist in EAMv2.
Through a consistent comparison between the models and satellite observations using the satellite simulator in EAMv1 and EAMv2, researchers identified that the simulated cloud phase has substantially improved in EAMv2. The impact of individual physics parameterization changes on simulated high-latitude clouds was examined with carefully designed sensitivity experiments. This study highlights the impact of deep convection parameterization changes on high-latitude mixed-phase clouds, which received little attention before. This study also suggests the importance of continuous development of cloud microphysics in climate models to represent the cloud phase at high latitudes accurately.
This study evaluated the simulated cloud phase in EAMv1 and EAMv2 by comparing with the GCM-Oriented Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation Cloud Product (CALIPSO-GOCCP) observations. The CALIPSO simulator was used to facilitate the consistent comparison of cloud quantities between the models and observations. The impact of individual new physics features incorporated into the EAMv2 model was also examined through sensitivity experiments. This study showed that the overestimated low-level supercooled liquid clouds largely contribute to the positive total cloud bias in the Arctic in EAMv2, which is the same as in EAMv1. On the other hand, the negative biases in ice-phase clouds in EAMv1 are much improved in EAMv2 due to the modified Wegner-Bergeron-Findeisen (WBF) process and the new convective trigger in EAMv2. This study highlights the impact of the changed convection scheme on high-latitude mixed-phase clouds and the need to further improve cloud microphysics for a better cloud phase simulation in Earth system models.