Atmospheric composition observed from a constellation of LEO and GEO hyperspectral infrared sounders onboard FengYun satellites

In recent years, a constellation of hyperspectral infrared sounders has been successfully launched into LEO and GEO orbits on board China’s FengYun meteorological satellites. The Geostationary Interferometric Infrared Sounder (GIIRS) on board the FengYun-4 (FY-4) satellites scans the East Asian region every two hours. The Hyperspectral Infrared Atmospheric Sounder (HIRAS) on board the FengYun-3 (FY-3) series of satellites forms a constellation in dawn-dusk, mid-morning and afternoon sun-synchronous orbits. This provides six global thermal infrared observations per day, with equatorial overpass times of 5:30 am/pm (FY-3E), 10:00 am/pm (FY-3F) and 2:00 am/pm (FY-3H) respectively.

In the first half of this presentation, we will introduce the ozone products (total columns and profiles) from GIIRS which are retrieved from the 9.6 μm absorption band via optimal estimation algorithm. These retrievals have been rigorously validated against ground-based measurements, multi-satellite retrievals, and reanalysis datasets. Importantly, GIIRS exhibits peak vertical sensitivity in the upper troposphere/lower stratosphere (UTLS) region, providing unique capabilities for investigating stratosphere-troposphere transport (STT). In theory, FY-4B/GIIRS's 2-hourly ozone data can provide detailed information about ozone changes during STT events, enabling STT's impact on tropospheric ozone to be measured more accurately.

In the second half of this presentation, we will introduce the ammonia (NH₃) retrieval data products from FY-3E, the world's first operational meteorological satellite in a dawn-dusk orbit for civil use. FY-3E provides global observations twice daily, at around 05:30 and 17:30 local solar time. Using the optimal estimation method, we have retrieved daily global NH₃ maps from January 2023 to the present. Our retrievals reveal significantly elevated total columns of NH₃ during dawn and dusk in several major source regions. These regions exhibit spatial patterns and seasonal variability that are similar to those observed by IASI and CrIS. Notably, higher total columns are retrieved at dusk over some important source regions compared with mid-morning and afternoon observations, potentially due to more intense emissions and diurnal temperature variations. Combining these observations with data from mid-morning (e.g. IASI) and afternoon (e.g. CrIS) satellites will significantly enhance our understanding of the nitrogen cycle.