Articles | Volume 16, issue 14
Research article
26 Jul 2016
Research article |  | 26 Jul 2016

Large XCH4 anomaly in summer 2013 over northeast Asia observed by GOSAT

Misa Ishizawa, Osamu Uchino, Isamu Morino, Makoto Inoue, Yukio Yoshida, Kazuo Mabuchi, Tomoko Shirai, Yasunori Tohjima, Shamil Maksyutov, Hirofumi Ohyama, Shuji Kawakami, Atsushi Takizawa, and Dmitry Belikov

Abstract. 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 Observing 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.

The analysis of surface CH4 concentrations observed at three monitoring sites around the Japan archipelago 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. This analysis demonstrates the capability of GOSAT to monitor an XCH4 event on a synoptic scale. We anticipate that the synoptic information of XCH4 from GOSAT data contributes to improve our understanding of regional carbon cycle and the regional flux estimation.

Short summary
Greenhouse gases Observing SATellite (GOSAT) was launched to monitor CO2 and CH4 concentrations from the space. This paper analyses an extremely high XCH4 event over Northeast Asia observed by GOSAT in the summer of 2013. Results indicate that the high XCH4 event was caused by fast transport of CH4-rich air from East China to Japan due to anomalies of north Pacific high-pressure system over East Asia. This study demonstrates the capability of GOSAT to detect an XCH4 event on a synoptic scale.
Final-revised paper