Start
April 5, 2019 - 3:00 pm
End
April 5, 2019 - 4:30 pm
Categories
Convective Meteorology (Mesoscale Dynamics)Effects of the Representation of Rimed Ice in Bulk Microphysics Schemes on Polarimetric Signatures
Marcus Johnson
Friday, April 5th
3:00pm/NWC 5600
Abstract: Many flavors of multi-category, multi-moment bulk microphysics schemes (BMPs) are available for storm-scale modeling and have various treatments of rimed ice. In this study, we compare three two-moment schemes available in the WRF model – Milbrandt-Yau (MY2), National Severe Storms Laboratory (NSSL), and the two-category configuration of the Predicted Particle Properties (P3) scheme – focusing on differences in rimed-ice representation and their impacts on surface rain and ice. Idealized supercell simulations were performed. A polarimetric radar data simulator is used to evaluate their ability to reproduce the ZDR arc and hail signature in the forward flank downdraft, well-known supercell polarimetric signatures that are potentially sensitive to rimed-ice parameterization.
Both the MY2 and NSSL schemes simulate enhanced ZDR near the supercell’s southern flank, but neither scheme simulates a classic ZDR arc. Surface ZDR in the default P3 scheme is homogenous in the supercell’s forward flank, and is due to the scheme’s restrictive minimum rain particle size distribution (PSD) slope bound preventing the presence of larger drops creating a ZDR arc. Only the NSSL scheme simulates the correct location of the hail signature in the forward flank downdraft. Larger hail in MY2 sediments to the surface compared to previous iterations of the scheme, but creates a ZDR disruption near the storm’s southern edge. The sedimentation of large ice in the default P3 scheme is limited by a restrictive ice mean diameter limiter within the scheme, precluding the scheme’s ability to reduce ZDR near the surface.