Details

Autor(en) / Beteiligte

• Xie, Shaocheng
• Liu, Xiaohong
• Zhao, Chuanfeng
• Zhang, Yuying

Titel

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

Ist Teil von

• Journal of climate, 2013-08, Vol.26 (16), p.5981-5999

Ort / Verlag

Boston, MA: American Meteorological Society

Erscheinungsjahr

2013

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• 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.