Short-Range Prediction of Squall-Line-Induced Heavy Rainfall: An Added Impact of GPS RO to FY-4A AGRI Data Assimilation

Abstract The GPS radio occultation technique has prompted a new era as GPS receivers are placed onboard traditional polar-orbiting operational environmental satellites and newly emerging commercial small satellite constellations. With high vertical resolutions of a few hundred meters, GPS radio occultation-observed refractivity profiles effectively complement the geostationary satellite observations of infrared brightness temperatures at high horizontal resolutions (∼2 km) for data assimilation in numerical weather prediction. In this study, numerical experiments are performed to assimilate radio occultation (RO) refractivity observations from FY-3D / FY-3E , MetOp-B/MetOp-C , COSMIC-2 , SPIRE, and GeoOptics and brightness temperature observations at channels 9 (6.25 μ m) and 10 (7.1 μ m) from the Advanced Geosynchronous Radiation Imager (AGRI) onboard FY-4A . The benefits of adding the refractivity to the brightness temperature observations for improving quantitative precipitation forecasts (QPFs) of two squall-line cases over eastern China are shown using the Weather Research and Forecasting Model and the Gridpoint Statistical Interpolation analysis system. In the first case, the squall line was caused by a superposition of cold and dry air advection behind an upper-level trough over low-level warm and humid air by a low-level jet. A combined assimilation of the GPS RO and FY-4A AGRI observations produced a skillful forecast of the squall-line distribution, characterized by a warm zone 100–300-km long ahead of a cold front near the ground; this led to more consistent improvements in the forecast of a narrow band of squall-line thunderstorms than those from two separate assimilations. The threat scores of 24-h QPFs associated with both squall-line cases are significantly improved, especially for heavier rainfall events.