Sensitivity of CAM5-simulated Arctic clouds and radiation to ice nucleation parameterization

• Published in: Journal of Climate
• Main Authors: Xie, Shaocheng, Liu, Xiaohong, Zhao, Chuanfeng, Zhang, Yuying
• Language: unknown
• Published: 2021
• Subjects: 54 ENVIRONMENTAL SCIENCES; Arctic
• Online Access: http://www.osti.gov/servlets/purl/1266669; https://www.osti.gov/biblio/1266669; https://doi.org/10.1175/JCLI-D-12-00517.1

Sensitivity of Arctic clouds and radiation in the Community Atmospheric Model, version 5, to the ice nucleation process is examined by testing a new physically based ice nucleation scheme that links the variation of ice nuclei (IN) number concentration to aerosol properties. The default scheme parameterizes the IN concentration simply as a function of ice supersaturation. The new scheme leads to a significant reduction in simulated IN concentration at all latitudes while changes in cloud amounts and properties are mainly seen at high- and midlatitude storm tracks. In the Arctic, there is a considerable increase in midlevel clouds and a decrease in low-level clouds, which result from the complex interaction among the cloud macrophysics, microphysics, and large-scale environment. The smaller IN concentrations result in an increase in liquid water path and a decrease in ice water path caused by the slowdown of the Bergeron–Findeisen process in mixed-phase clouds. Overall, there is an increase in the optical depth of Arctic clouds, which leads to a stronger cloud radiative forcing (net cooling) at the top of the atmosphere. The comparison with satellite data shows that the new scheme slightly improves low-level cloud simulations over most of the Arctic but produces too many midlevel clouds. Considerable improvements are seen in the simulated low-level clouds and their properties when compared with Arctic ground-based measurements. As a result, issues with the observations and the model–observation comparison in the Arctic region are discussed.