[A-CG37] Satellite Earth Environment Observation

[ACG37-10] The Insights from Twenty Years of AIRS Radiances and an Outlook for the Incoming Decade: a Climate Perspective

*Xianglei Huang¹, Xiuhong Chen¹, L. Larrabee Strow², Chongxing Fan¹, Norman Loeb³, Seiji Kato³ (1.University of Michigan at Ann Arbor, 2.University of Maryland at Baltimore County, 3.NASA Langley Research Center)

Keywords:hyperspectral sounding, climate trend, radiative feedback, radiative forcing

Atmospheric Infrared Sounder (AIRS) aboard the NASA Aqua satellite has been operating since September 2002. Its information content, superb instrument performance, and dense sampling pattern make the AIRS radiances an unprecedentedly invaluable data set for climate studies. We use two studies here to illustrate its merit in climate studies. First, the trends of global-mean, nadir-view, and clear-sky radiances from two decades of AIRS observations are studied, together with the counterparts of synthetic radiances based on two reanalyses, ECMWF ERA5 and NASA GEOS V5.4.1. The AIRS observation shows statistically significant negative trends in most of its CO₂ channels, positive but non-significant trends in the channels over the window regions, and statistically significant positive trends in some of its H₂O channels. The best agreements between observed and reanalysis radiance trends are seen over the CO₂ tropospheric channels, while the trends over the CO₂ stratospheric channels are opposite between the observations and reanalyses. ERA5 results largely agree with the AIRS observation over the H₂O channels, but this is not the case for GEOS V5.4.1. Second, using ERA5 reanalysis data, other A-Train observations, and greenhouse gas measurements from NOAA, we derived the spectral radiative forcing due to greenhouse gas increases in the last 20 years, and short-term spectral radiative feedbacks of lapse rate, water vapor, and cloud over the same period. The combined spectral radiative forcings and radiative feedbacks agree well with the spectral flux trend derived from the AIRS L3 spectral OLR product. The most significant discrepancies happened in the far-IR region, a spectral region with no actual AIRS coverage (so its spectral flux has to be estimated using the mid-IR spectral flux directly inferred from AIRS radiance observations). The implications of two forthcoming far-IR missions, PREFIRE by NASA and FORUM by ESA, for resolving such far-IR discrepancies are then discussed.