Evaluation of satellite based rain rate retrieval during OLYMPEX

This study examines how well satellite retrievals capture the variability of rainfall under a wide-range of meteorological and topographic conditions during the 2015-2016 Olympic Mountains Experiment (OLYMPEX). First of all, we develop the best possible rain rate retrieval from ground-based polarimetric radars (including NASA’s NPOL and the KLGX NEXRAD) to create precipitation maps for the entire OLYMPEX field campaign. Rainmaps and rain statistics are developed over land and water sectors. A Z-R relationship is developed using the rain gauge network, NASA disdrometer array, and possibly the DOW X-band data. We also test and apply S-band polarimetric data for rain rate estimation. Accordingly, rain maps of a nominal spatial resolution of 1 km and temporal resolution of 10 mins are generated. During OLYMPEX, GPM overflew the experimental area a good number of times (12-13 for DPR and 20-25 for GMI) under different weather conditions, providing excellent opportunities for validating the GPM core satellite data against ground based observations. GPM DPR (2ADPR, 2Aku) and GMI (GPROF) near surface rain rate PDFs are compared to our derived rain maps over common areas. Our derived rain maps are also degraded to 4 km resolution to examine effects of the coarser GPM DPR observations. The retrieved DPR reflectivities are further validated against NPOL reflectivities at different levels, above and below freezing, using the CFAD technique (correcting for wavelength differences). DPR-NPOL and GMI-NPOL rain rate differences are then quantified as a function of location (ocean, coast, and mountains) and stage of frontal system (pre-frontal, frontal, and post-frontal sectors, determined by synoptic weather maps and the OLYMPEx sounding data obtained at NPOL). Hydrometeor retrievals from NPOL will be used to understand microphysical properties contributing to biased satellite retrieval scenarios.