Impact of radio occultation data on satellite radiance data assimilation performance in tropical cyclone formation forecast over the western North Pacific

This study explores the potential impact of global navigation satellite system (GNSS) radio occultation (RO) data on the performance of satellite radiance data assimilation for the tropical cyclone formation forecast over the western North Pacific. The forecast experiments of 32 tropical disturbances in September−October 2019 are performed through a regional model. Either assimilation of GNSS RO data, radiance data, or both of them can improve the forecast skill and environmental moisture of tropical cyclone formation. However, the interaction between radiance and GNSS RO data can further increase moisture throughout the forecast period, compared to the experiment with only radiance data assimilation. Moreover, the improved vorticity patterns are different between the experiments with GNSS RO data and with radiance data. When both the GNSS RO and radiance data are assimilated, the improved vorticity pattern tends to the pattern improved by GNSS RO data assimilation. This may be attributed to the anchoring effect of GNSS RO data on satellite radiance data assimilation. Although radiance data volume is much larger than GNSS RO data, the interaction between GNSS RO and radiance data in the data assimilation process can significantly improve forecast performance.