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Abstract
Fengyun4A is the first geostationary satellite with payload of the infrared hyperspectral sounder. The geostationary platform-based instrument can provide observational 3-dimensional fields of temperature and humidity with high scanning frequencies and spatial resolutions. The IR instrument-observed temperature (T) and relative humidity (RH) profiles are closely related to the cloud states. Radiosonde observations are used to validate the Fengyun4A T and RH profiles under different cloud-type sky conditions. The cloud-type information comes from the Himawari-8 satellite which has substantial observing overlap with Fengyun4A over Asia. Taking the radiosonde observation as the reference, Fengyun4A T profile has uncertainty of 2.1 K under clear sky, and 3.7 K under cloudy sky. When cloudy sky is divided into cloud-type skies, the categories have disparities in temperature biases, varying from positive to negative. It is found that most of cloud-type categories have uncertainties of 2.5–3.0 K. The RH profiles have an uncertainty of 18% under clear sky and 21% under cloudy sky in absolute value. On average, the RH biases show neural but positively biased at the dry side and negatively biased at the wet side in the scatter plot. The International Satellite Cloud Climatology Project (ISCCP) cloud type can help to extend the quality flag of the Fengyun4A temperature profile. The impacts from cloud types on IR sounding profiles should be considered in product development or applications.
Highlights
The variations of temperature, humidity, and clouds are interwoven in the Earth atmosphere system
Three independent datasets are used in the study: the temperature and humidity profiles of Geostationary Interferometric Infrared Sounder (GIIRS) onboard of FY4A, the ground-based radiosonde data and Himawari-8 cloud-type product, which contains the International Satellite Cloud Climatology Project (ISCCP) cloud-type variable
The data quality of FY4A temperature and humidity profile products is suggested with a quality flag by the Fengyun science team
Summary
The variations of temperature, humidity, and clouds are interwoven in the Earth atmosphere system. IR sounder at this spectral range can be used to measure temperature and humidity profile because of the absorption by CO2 and water. For the area focused on in this study, the average cloud fraction is about 61% over China region [20] Cloud properties such as phase, height, and optical depth impact the IR sounding retrieval. Physically-based radiative transfer models such as DISORT [24] are used to estimate the cloud radiative property at IR band so that the hyperspectral IR soundings can gather radiances data to estimate profiles under partial cloudy sky [25,26]. Three independent datasets are used in the study: the temperature and humidity profiles of GIIRS onboard of FY4A, the ground-based radiosonde data and Himawari-8 cloud-type product, which contains the ISCCP cloud-type variable. Radiosonde observation is used to validate the performance of GIIRS under the clear sky and ISCCP cloud-type skies
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