Three-Dimensional Wind Field Retrieval by Combining Measurements from Imager and Hyperspectral Infrared Sounder Onboard the Same Geostationary Platform

The Geosynchronous Interferometric Infrared Sounder (GIIRS) onboard Fengyun-4A (FY-4A) is the first geostationary hyperspectral infrared IR sounder. It can provide continuous three-dimensional (3D) data on atmospheric temperature, water vapor, and atmospheric horizontal wind fields at various altitudes by tracking water vapor movements. In this study, GIIRS data from FY-4A observations at 30-min intervals during Typhoon Maria (2018) were used. Our aim was to test a 3D horizontal wind field algorithm in both clear and partially cloudy skies, emphasizing the enhancement of 3D wind field retrieval from partially cloud-filled GIIRS footprints by incorporating collocated high-spatial resolution cloud products from the Advanced Geostationary Radiation Imager (AGRI) onboard the same platform. Independent ERA5 and CRA40 analyses, as well as radiosonde data, were used as reference data for verifying 3D horizontal wind field retrievals in both clear and partially cloudy skies. The results indicate that tropospheric wind fields can be obtained from GIIRS brightness temperature (BT) measurements from two consecutive times. In clear skies, the root mean square error (RMSE) is less than 1.5 m s⁻¹, with an absolute direction difference between retrievals and reference data of approximately 15° in this case. In partially cloudy skies, the RMSE is 1.5–1.7 m s⁻¹, with an absolute direction difference of approximately 20°. Compared with the traditional optical flow method, the GIIRS BT-based direct retrieval method exhibits superior accuracy, with smaller RMSE and direction absolute difference. When classified by cloud coverage (CC) and cloud-top pressure (CTP), a larger cloud cover or higher cloud top results in a greater RMSE. However, when CC and CTP are included as additional input parameters, RMSE decreased, indicating that high-spatial resolution AGRI cloud products can improve wind field retrieval accuracy in some cloud-covered areas. Finally, wind profile retrievals from the GIIRS BT-based method are consistent with wind profiles obtained through CRA40 analysis and dropsonde data, indicating the feasibility of deriving 3D horizontal wind fields from geostationary hyperspectral IR BT measurements.