Extremely high levels of column-averaged dry-air mole fractions of atmospheric methane (XCH₄) were detected in August and September 2013 over Northeast Asia (~ 20 ppb above the averaged summertime XCH₄ over 2009–2012, after removing a long-term trend), as being retrieved from the Short-Wavelength InfraRed (SWIR) spectral data observed with the Thermal And Near-infrared Sensor for carbon Observation-Fourier Transform Spectrometer (TANSO-FTS) onboard Greenhouse Gases

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... g Satellite (GOSAT). Similar enhancements of XCH₄ were also observed by the ground-based measurements at two Total Carbon Column Observing Network (TCCON) sites in Japan. <br><br> The analysis of surface CH₄ concentrations observed at three monitoring sites around the Japan islands suggest that the extreme increase of XCH₄ has occurred in a limited area. The model analysis was conducted to investigate this anomalously high XCH₄ event, using an atmospheric transport model. The results indicate that the extreme increase of XCH₄ is attributed to the anomalous atmospheric pressure pattern over East Asia during the summer of 2013, which effectively transported the CH₄-rich air to Japan from the strong CH₄ source areas in East China. The two Japanese TCCON sites, ~ 1000 km east-west apart each other, coincidentally located along the substantially CH₄-rich air flow from East China. The GOSAT orbiting with three-day recurrence successfully observed the synoptic-scale XCH₄ enhancement in the comparable accuracy to the TCCON data. This analysis demonstrates the capability of GOSAT to monitor an XCH₄ event on a synoptic scale.