P1.57 A novel, multiple liquid and ice hydrometeor species, hybrid- bulk/bin, three-moment microphysics parameterization scheme: Examples

Monday, 28 June 2010
Exhibit Hall (DoubleTree by Hilton Portland)
Matthew S. Gilmore, University of North Dakota, Grand Forks, ND ; and J. Straka

Some of the new features of the new model are summarized in this poster using column models as well as idealized three-dimensional simulations of lake-effect snowfalls, orographic precipitation, and supercells, which generate all of the species. The purpose of the column models is to show examples of how a hybrid-bulk/bin scheme can be joined with a three-moment scheme to better represent time-evolving distribution shapes in the case of graupel accreting rain above the melting level, and evaporation of rain below cloud base. Traditionally the case graupel accreting rain above the melting later is a three-body process where two hydrometeors species interact and produce a third species such as hail. In reality faster falling large graupel can capture small slow falling rain and vice-versa. Better than the Wisner and Mizuno approaches for dealing with the velocity difference in the collection growth equation, the hybrid-bulk/bin parameterization allows for differential collection of particles instead of the whole spectrum of rain collecting graupel and vice-versa. For evaporation of rain below the cloud base, the number concentration and mixing ration lost to evaporation is done in bin space so an accurate accounting of rain loss can be made. Then, for both examples described an accurate accounting of the change in reflectivity also can be made allowing a new shape parameter to be diagnosed for rain. A couple of other idealized studies with the column model involving sedimentation are also shown. These show the importance of the three-moments and the effect in the varying shape parameter on hydrometeor.

In three-dimensional tests the scheme also shows promise for correctly simulating the differences in ice crystal habits and snow aggregates as a function of distance from the shoreline in idealized lake-effect snow cases and orographic snow cases. Early studies show proper ice crystal initialization for given supersaturations over ice. Then aggregation occurs with dendrites being most active in the aggregation process. Other shapes aggregate far less easily than dendrites. The crystals and snow aggregates that fallout of a snow band that develops over a Lake Michigan like lake can be compared with some recent observations made south of Lake Michigan. Other important tests include idealized orographic snowfall and a supercell simulation that is conducive to tornado cyclone development. These will be shown on the poster.

- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner