Evaluation of Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR) Heavy Ice Precipitation Products

Abstract In version 7 of the Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) released in December 2021, several parameters are related to solid precipitation, such as flagHail, flagGraupelHail, and the MSindex. The flagHail detects hail and/or graupel, whereas the MSindex detects multiple scattering that can be used for hail detection because multiple scattering tends to occur with hail. In this study, four products related to solid precipitation were compared and evaluated, including the product named flagHeavyIcePrecip introduced in version 6 (V06) and the three previously mentioned products from V07. Stratiform precipitation contamination was recorded by flagGraupelHail and the MSindex. Given that flagHeavyIcePrecip allows stratiform precipitation because it targets large snowflakes, hail, and graupel, the separation of snowflake and hail/graupel types is conducted by applying a simple method to convective precipitation. The number of detections was small for flagHail and MSindex, which were less than 0.07% and 0.04% of total precipitation pixels, respectively. Meanwhile, the number of occurrences of flagGraupelHail and flagHeavyIcePrecip was 10 times larger. There was relatively little overlap between products. Multiple scattering appeared as a knee structure of the dual-frequency ratio from the measured radar reflectivity factor (DFRm) that can be seen in the MSindex, flagHail, and flagHeavyIcePrecip of convective precipitation. This indicates that each algorithm detects similar precipitation types including when the overlapping pixel numbers are relatively limited. The flagHeavyIcePrecip was distributed in the tropical region and midlatitudes, indicating the potential detection of graupel from the winter shallow convective system. Significance Statement This study evaluated large solid precipitation products from a dual-frequency precipitation radar onboard the Core Observatory of the Global Precipitation Measurement mission. Solid precipitation products contain information on hail and graupel, which are important for assessing the effects of climate change. Therefore, it is beneficial for users to evaluate these products in terms of their occurrence, the vertical precipitation profile, and the overlap between products. In this study, we examined the occurrence and vertical distribution of the radar reflectivity factor and the dual-frequency ratio of each product and have proposed algorithm improvements.