Uncertainties in simulated Z-S relationships due to ice particle model and particle size distribution variations with application to active spaceborne remote sensing of snowfall

CloudSat's Cloud Profiling Radar (CPR) is currently providing routine observations of clouds and precipitation and offers an unprecedented opportunity to study the distribution and intensity of snowfall at higher latitudes on a global basis. The upcoming Global Precipitation Measurement (GPM) mission will feature a dual-frequency radar platform that will also provide global snowfall observations. In order to transform reflectivity observations from active microwave instruments into useful geophysical parameters like snowfall rates, appropriate reflectivity (Z) to snowfall rate (S) conversions are needed and increased understanding of their attendant uncertainties must be gained. This study explores the potential uncertainty in Z-S relationships due to the assumed ice particle model chosen to represent backscattering properties of frozen hydrometeors. Over twenty different ice particle models - comprised of both non-spherical and spherical representations of frozen particles – are used to demonstrate the possible variability of Z-S relationships due to the assumed ice particle model. Additionally, different ice particle size distribution (PSD) parameterizations are utilized to illustrate another potentially large source of uncertainty in Z-S relationships. Comparisons between commonly used exponential PSD relationships to parameterizations that more effectively model the non-exponential behavior of typical frozen PSD's at smaller particle sizes will be shown with special emphasis placed on applications to CloudSat and GPM radar observations.