School of Meteorology (Defense)

A Comparison of Microphysical Parameterization Sensitivities in Three Comma-Head Snow Events and Evaluation of Scheme Solutions with PIREPs

Kristen Cassady
OU School of Meteorology

13 September 2013, 9:00 AM

National Weather Center, Room 4140
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Numerical model experiments are conducted to assess how the presence of supercooled liquid water (SLW) is dependent on the choice of microphysical parameterization for select winter storms that were observed to have elevated regions of SLW. The schemes considered include the Thompson, Milbrandt-Yau, Morrison, and National Severe Storms Laboratory (NSSL) microphysics parameterizations. The Thompson scheme routinely produces less SLW than the other three schemes. Sensitivity experiments reveal this difference is in large part a consequence of aggressive scavenging of cloud water from snow. In some environments, the Morrison scheme produces considerably more SLW than the other parameterization schemes. It is unclear why this happens. The output from each experiment is compared to aviation pilot reports of aircraft icing to determine which scheme yields the most accurate results. According to all statistical measures that were tried, the Morrison scheme performs the best. However, the results are not drastically different between the schemes.

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