Application and Evaluation of A Dual-polarization Radar Rainfall Algorithm in Complex Terrain during NASA IPHEx Field Campaign

In order to characterize warm season orographic precipitation regimes, and the relationship between precipitation regimes and hydrologic processes in regions of complex terrain, the U.S. National Aeronautics and Space Administration (NASA) Global Precipitation Measurement (GPM) ground validation (GV) team had conducted the Integrated Precipitation and Hydrology Experiment (IPHEx) in the southern Appalachian Mountains from May 1 to June 15, 2014. A large number of ground instruments and advanced dual-polarization radars were deployed to collect detailed measurements of surface precipitation while simultaneously collecting data from satellites passing overhead.

Dual-polarization radar measurements offer a number of advantages for quantitative precipitation estimation (QPE) over traditional single-polarization radar by revealing more characteristics about raindrop size distribution (DSD) and different hydrometeor types. However, it is still challenging to determine the most appropriate rainfall relation to employ for a given set of dual-polarization observations. In addition, the complex terrain in southern Appalachian has made QPE in this region more difficult, due to the sampling issues. In particular, radar beams are often blocked or scan above the melting layer while rain gauge density is often too low to capture the complex distribution of precipitation.

In this paper, a dual-polarization radar rainfall methodology is developed for accurate precipitation estimation. In this method, radar beam blockage cause by terrain will be corrected based on the self-consistency of dual-polarization measurements. The vertical profiles of reflectivity will be identified that takes into account the radar sampling. Specific rainfall relations are then selected based on hydrometeor classification algorithm. Dual-polarization data collected from NASA POLarimetric weather radar (NPOL) and National Weather Service (NWS) Weather Surveillance Radar -1988 Doppler (WSR-88DP) during IPHEx will be used for deriving rainfall products for this complex terrain region. The NASA dual tipping-bucket rain gauges deployed for this field experiment will be used for evaluation purposes.