Polarimetric radar signatures from RAMS microphysics

Recent modelling studies have shown the importance of microphysics in modulating strom structure and precipitation evolution in convective storms. Advances in radar polarimetric methods, on the other hand, have shown its usefulness in studies of some important aspects of precipitation formation and evolution including hydrometeor type classification. The Regional Atmospheric Modeling System (RAMS) has a sophisticated microphysics scheme including 2-moment prognosis of mixing ratio and number concentration of the various hydrometeor species, emulation of a bin-resolving model in terms of collection and sedimentation, and simulation of source/sink functions of CCN and GCCN and their activation in cloudy updrafts.

A polarimetric radar module has been developed that uses the RAMS microphysical predictions to diagnose the radar observables such as reflectivity (Zh), differential reflectivity (Zdr), linear depolarization ratio (LDR), specific differential phase (Kdp) and copolar correlation coefficient . Several case studies of polarimetric radar signatures based on RAMS simulations will be described, in particular, the signatures associated with enhanced aerosol concentrations (CCN and GCCN) associated with convection over urban areas, and the impact of varying hail sizes in supercell simulations. We will also evaluate the current radar-based hydrometeor classification schemes using the RAMS model for validation.