A31D-0062: Atmospheric Methane over the Arctic Ocean: Satellite Data
Authors: Leonid Yurganov1, Xiaozhen (Shawn) Xiong2, 3, Steven C Wofsy4
Author Institutions: 1. Physics, JCET, Baltimore, MD, USA; 2. I.M.Systems Group, Rockville, MD, USA; 3. NOAA/NESDIS/STAR, Camp Springs, MD, USA; 4. School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
Global increase of methane (CH4) that started in 2007-2008 after a decade of stability, requires investigation and explanation. Location and nature of growing methane source(s) is still under discussion. In this report methane satellite data of two instruments for the Arctic Ocean are analyzed. The US grating spectrometer Atmospheric InfraRed Sounder (AIRS), version 5, standard data, at the Aqua satellite has been delivering CH4 data for the upper troposphere (around 350-400 hPa) since 2002. The European Infrared Atmospheric Sounding Interferometer (IASI) is operational since 2008; methane mixing ratios are retrieved by NOAA; CH4 profiles averaged between the surface and the altitude ~4 km are analyzed here. The IASI satellite data were validated with the aircraft in situ measurements during the Arctic campaigns of the Hiaper Pole-to-Pole Observations (HIPPO) project. Long-term monthly global and hemispheric means records obtained by AIRS show a relative stability before 2007 and methane growth afterwards. Generally, Northern and Southern hemispheric methane averages have been growing similarly; however, in 2009 and in 2011-2012 Northern Hemisphere methane was increasing faster. IASI data for the autumn months (October-November) clearly indicate Eurasian shelf areas of the Arctic Ocean as a significant methane emitter. The maximal methane concentrations were found over Kara and Laptev Seas. According to IASI data, during the last three years in autumn time, methane over Eurasian shelf has been increased by 25 ppb, over the N. American shelf, by 23 ppb, and over the land between 50 N and 70 N for both Eastern and Western hemispheres, by 20 ppb.