Airborne Radio Occultation Data Retrieved from Multi-Global Navigation Satellite Systems in Atmospheric River Reconnaissance Campaigns over the Northeast Pacific

To better understand and forecast the intense rainfall in the western United States brought by Atmospheric Rivers (ARs), the Atmospheric Rivers Reconnaissance missions deploy aircraft to measure pressure, temperature, moisture, and wind information from dropsondes that are released below the aircraft. This paper describes an Airborne Radio Occultation (ARO) observation system installed on the same aircraft that uses Global Navigation Satellite System (GNSS) signals to retrieve additional profile observations during flights. By collecting data from multiple constellations, including the Global Positioning System (GPS), the European Galileo, Russian Glonass and Chinese Beidou systems, approximately 42 slant profiles are retrieved during each 7-8 hour flight, providing high-quality information about the temperature and moisture in the AR environment below flight level and in the 500 km region surrounding the flight track. The ARO observation system collects complementary data to the conventional dropsondes without additional expendable costs, to help understand the physics and dynamics of ARs, and provide a better link between the point measurements made by the dropsondes and the larger-scale environment. This work describes the sampling characteristics of ~1700 refractivity profiles from four years of campaigns (2018-2021) and describes the data quality in comparison to model reanalyses and dropsondes. The AR is a highly heterogeneous atmospheric structure, therefore to avoid assumptions made in the retrieval process, we are developing a 2D observation operator for use in data assimilation. Results describing the observation errors as quantified by the observation operator will be presented, as well as progress towards data assimilation. The dataset is freely available to contribute to improved AR and rainfall prediction.