Vertical Profiling of Precipitation Characteristics for GPM Ground Validation

Characterization of the vertical structure/variability of precipitation and resultant microphysics is critical in providing physical validation of space-based precipitation retrievals. In support of NASAs Global Precipitation Measurement (GPM) mission Ground Validation (GV) program, a Precipitation Research Facility (PRF) has been established at NASA Goddard Space Flight Center Wallops Flight Facility (WFF) at Wallops Island, Virginia. The GPM PRF has deployed numerous precipitation measuring instruments including rain gauges, disdrometers, profilers and ground-based radars, including NASAs dual-polarization (NPOL) S-band radar. The NPOL radar is located in Newark, MD, approximately 38 km north-northeast of WFF, and provides Plan Position Indicator (PPI) scans over a high-density gauge network and other instruments, as well as multiple high-resolution Range Height Indicators (RHI) scans over the WFF main base. These RHI scans are made over several deployed rain gauges and disdrometers (Parsivel-2and Two-Dimensional Video Disdrometer (2DVD)). Temporal resolution is on the order of 3 minutes, while the spatial resolution is 125 m along each range gate and approximately 0.2 degrees in the vertical. When precipitation is present, NPOL obtains very high-resolution vertical profiles of radar observations (e.g. reflectivity (ZH) and differential reflectivity (ZDR)), from which important particle size distribution parameters are retrieved such as the mass-weight mean diameter (Dm) and the intercept parameter (Nw). These data are then averaged horizontally to match the nadir resolution of the dual-frequency radar (DPR; ~5 km) on board the GPM satellite. The GPM DPR, Combined, and radiometer algorithms (such as GPROF) rely on functional relationships built from assumed parametric relationships and/or retrieved parameter profiles and spatial distributions of particle size (PSD), water content, and hydrometeor phase within a given sample volume. Thus, the NPOL-retrieved profiles provide an excellent tool for characterization of the vertical profile structure and variability during GPM overpasses. In this study, we will use many such overpass comparisons to quantify an estimate of the true sub-IFOV variability as a function of hydrometeor and rain type (convective or stratiform).