Convective Meteorology (Mesoscale Dynamics)

Comparison of Polarimetric Signatures Simulated using Two-Moment Bulk Microphysics Schemes in WRF in Idealized Supercell Storms

Marcus Johnson
OU School of Meteorology

06 March 2015, 2:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Numerical weather prediction models contain several microphysics parameterization options, the choice of which becomes increasingly important as the model resolution increases toward convection-resolving scales. The performance of several partially or fully two-moment (2M) schemes, chosen because of their well-documented advantages over one-moment (1M) schemes, is evaluated using the presence and magnitude of well-known supercell thunderstorm polarimetric radar signatures: the ZDR and KDP columns, the ZDR arc, the midlevel ZDR and ρHV rings, the hail signature in the forward flank downdraft, and the KDP foot. Idealized supercell thunderstorm simulations are performed using the WRFV3.5.1 model, while polarimetric variables are computed from model output using a polarimetric radar simulator. It is found that microphysics schemes with a 1M rimed-ice category were unable to simulate the ZDR arc, despite containing a 2M rain category. It is also found that a hail hydrometeor category was necessary to replicate the low- ZDR hail signature. In the majority of the microphysics schemes evaluated, only small amounts of wet graupel were able to reach the surface, which did not reduce ZDR. The most realistic signatures overall were found with microphysics schemes that were fully 2M with a separate hail hydrometeor category.

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