Sensitivity of CAM5-Simulated Arctic Clouds and Radiation to Ice Nucleation Parameterization

• Published in: Journal of Climate
• Main Authors: Xie, S., Liu, Xiaohong, Zhao, C., Zhang, Y.
• Format: Other Non-Article Part of Journal/Newspaper
• Language: English
• Published: University of Wyoming. Libraries 2013
• Subjects: Aerosol properties; Cloud radiative forcing; Community atmospheric model; Ground based measurement; Liquid water paths; Mid-latitude storms; Number concentration; Top of the atmospheres; Atmospheric radiation; Light polarization; Nucleation; Sensitivity analysis; Ice; aerosol; cloud microphysics; comparative study; ground-based measurement; satellite data; supersaturation; Arctic; Engineering
• Online Access: https://hdl.handle.net/20.500.11919/714; https://doi.org/10.1175/JCLI-D-12-00517.1

©2013 American Meteorological Society. 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. Issues with the observations and the model- observation comparison in the Arctic region are discussed.