Using Simulated Crystal Aggregates to Represent Snow and Melting Precipitation in the GPM Combined Radar-Radiometer Algorithm

In previous work by the co-authors, pristine ice crystals with different habits were simulated using a 3D particle growth model. A computational method for simulating particle collection was then applied to create nonspherical aggregates of the crystals with liquid-equivalent diameters ranging from 164 μm to 3.1 mm (260 μm to 14.3 mm maximum dimension). These aggregates were characterized by mass-size relationships that covered the range observed in airborne microphysics probe studies. Also, it was demonstrated that much greater consistency between the simulated bulk scattering signatures of the aggregates and coincident airborne radar and radiometer observations could be achieved, relative to what was possible using earlier homogeneous spherical ice/air particle models. Recently, the aggregate particle database was extended to include the geometries and scattering properties of aggregates with diameters up to 5 mm liquid-equivalent (or 22 mm maximum dimension). The extended database made it possible to adequately represent the bulk scattering properties of nonspherical aggregate particles in the Global Precipitation Measurement (GPM) mission's satellite combined radar-radiometer precipitation estimation algorithm. Relative to the bulk scattering signatures derived from spherical ice/air models, the signatures derived from the nonspherical aggregates were much more consistent with coincident radar and radiometer observations from GPM. A subset of the nonspherical aggregates have been computationally melted, and their calculated scattering properties have been introduced into a 1D thermodynamic model that simulates the vertical distributions of mixed-phase particle size spectra and liquid fractions in the melting layers of stratiform precipitation regions. Results of this recent work will be presented at the conference.