Are thermal infrared measurements of CO 2 from GOSAT andIASI over the Arctic Ocean in summer able to detect climaticchange

The Arctic Ocean is a region where the impact of global change is detected on an annual basis by a wide variety of observations: buoys, research vessels and aircrafts. But the large area involved and the need of frequent sampling make polar orbiting satellites a prime source of observations for documenting the corresponding fast changes, especially in summer. Sun reflected measurements in the shortwave infrared (SWIR) region of the spectrum are not very sensitive because of the elevated solar zenith angle. In these conditions, thermal infrared (TIR) measurements using spectra collected by high spectral resolution nadir sounders are a good complement to document the high latitudes regions. In the present work the spectra acquired by the TANSO-FTS instrument on GOSAT and by the IASI instrument on the MetOp platforms have been used to test the retrieval capabilities of these Fourier transform spectrometers to retrieve the carbon dioxide column averaged mixing ratio XCO 2 as well as the sea surface temperature (SST) used as an inversion diagnostic. Results for 3 observing periods in summer (July, August, September) and 6 years (2010 to 2015) have been obtained in the latitude range 68N to 82N over open water (no pack ice). The retrieved products have been analyzed from a climatologic point of view to assess inter-annual variability and trends of TIR derived XCO 2 and SST zonal averages (3 summer months and 7 bins of 2° in latitude). Results will be described and compared with other sources of information. This type of study is important for preparing future satellite missions like IASI-NG (a follow-on of IASI) and GOSAT-2 (a follow-on of GOSAT). Some specific regional Arctic Ocean basins will be compared to the zonal climatologies.