Journal
JOURNAL OF CLIMATE
Volume 26, Issue 16, Pages 5981-5999Publisher
AMER METEOROLOGICAL SOC
DOI: 10.1175/JCLI-D-12-00517.1
Keywords
Aerosols; Cloud microphysics; Ice crystals; Climate models; Cloud parameterizations; Model evaluation; performance
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Funding
- Earth System Modeling Program of the Office of Science at the U.S. Department of Energy (DOE)
- Atmospheric Radiation Measurement Program of the Office of Science at the U.S. Department of Energy (DOE)
- DOE Office of Science Atmospheric System Research (ASR) Program
- DOE Office of Science Earth System Modeling Program
- DOE, Office of Science, Office of Biological and Environmental Research by Lawrence Livermore National Laboratory [DE-AC52-07NA27344]
- Battelle Memorial Institute [DE-AC06-76RLO 1830]
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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.
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