The Influence of Sub‐Footprint Cloudiness on Three‐Dimensional Horizontal Wind From Geostationary Hyperspectral Infrared Sounder Observations

Radiance measurements from a geostationary hyperspectral infrared sounder (GeoHIS) with high temporal resolution not only provide a continuous weather cube of atmospheric temperature and moisture information at different pressure levels, but also enable derivation of three-dimensional (3D) horizontal winds by tracking atmospheric water vapor features. However, GeoHIS radiances are influenced by sub-footprint cloudiness, which needs to be considered in tracking the moisture features for deriving the atmospheric wind fields. By combining the collocated high spatial resolution cloud information from an imager onboard the same platform, the 3D horizontal wind retrievals can be improved, and the influence of sub-footprint cloudiness on winds can be quantified for better applications. Using data from the Advanced Geostationary Radiation Imager (AGRI) and Geostationary Interferometric Infrared Sounder onboard the same experimental geostationary satellite Fengyun-4A, it is found that 3D horizontal wind retrievals can be derived under both clear and partially clear skies with reasonable accuracy. Sub-footprint cloud information provides noticeable improvement in wind retrievals; higher/lower clouds have more/less influence while thicker/thinner clouds have more/less influence, respectively, on the wind product. The sub-footprint cloudiness (cloud-top pressure and cloud coverage) provides a good indication of the quality flag for quantitative applications of the 3D horizontal wind product.