Microphysical Modeling

Research activities related to microphysical modeling are designed to improve the simulation of cloud water (including supercooled cloud water), rain and drizzle, freezing rain and freezing drizzle, snow, snow pellets, ice pellets and hail in RUC and WRF models. Supercooled cloud water and freezing drizzle are emphasized due to their importance to the FAA-sponsored In-Flight Icing program at RAL. This research also is designed to improve forecasts of winter weather conditions at the ground, as well as improving Quantitative Precipitation Forecasting (QPF).  Current sources of funding are the FAA and NSF.

FY06 Accomplishments:

Figure 1. Schematic showing the structure of the WRF model with urban-canopy parameterization. Application of the WRF/Noah/Urban coupled modeling system over Salt Lake City and surrounding complex terrain.

A new bulk microphysical parameterization (BMP) has been developed for WRF (and MM5). The new scheme incorporates a large number of improvements to both physical processes and computer coding. In general, the new snow treatment reduces ice supersaturation at high altitudes (low temperatures) and within deep glaciated clouds but enhances supercooled liquid water in shallow, relatively warm clouds. This aspect, combined with a rain size distribution intended to mimic both classical and non-classical precipitation-formation mechanisms, results in improved forecasts of freezing drizzle and aircraft icing. Another unique feature of the new scheme is the use of a single hydrometeor category to simulate both graupel and hail. Initial simulations of convective squall lines indicate improved representation of leading convection with trailing stratiform.  The new scheme has been adapted to both numerical cores of the WRF model (ARW and NMM) and was run for nearly 240 simulations (one month from four seasons, run at 0000 and 1200 UTC each day).  Results of these simulations will be investigated in 2007.  

FY07 Plans:

A number of improvements will be made to the new bulk microphysics scheme:  prediction of second moment (number concentration) for cloud water and rain will be added, as will a variable for aerosols and their activation (into cloud water  and/or cloud ice).  The new bulk scheme will also be compared with I. Geresdi's bin microphysics scheme and other 2-moment schemes.  Analysis of field project data from IMPROVE, AIRS2 will continue, and support for the ICE-L field project (March 2007) will be provided. Case studies from ICE-L will be investigated with regard to sensitivity to ice initiation.