Global column-averaged methane mixing ratios from 2003 to 2009 as derived from SCIAMACHY: Trends and variability

Abstract

After a decade of stable or slightly decreasing global methane concentrations, ground‐based in situ data show that CH4 began increasing again in 2007 and that this increase continued through 2009. So far, space‐based retrievals sensitive to the lower troposphere in the time period under consideration have not been available. Here we report a long‐term data set of column‐averaged methane mixing ratios retrieved from spectra of the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument onboard Envisat. The retrieval quality after 2005 was severely affected by degrading detector pixels within the methane 2ν3 absorption band. We identified the most crucial problems in SCIAMACHY detector degradation and overcame the problem by applying a strict pixel mask as well as a new dark current characterization. Even though retrieval precision after the end of 2005 is invariably degraded, consistent methane retrievals from 2003 through 2009 are now possible. Regional time series in the Sahara, Australia, tropical Africa, South America, and Asia show the methane increase in 2007–2009, but we cannot yet draw a firm conclusion concerning the origin of the increase. Tropical Africa even seems to exhibit a negative anomaly in 2006, but an impact from changes in SCIAMACHY detector degradation cannot be excluded yet. Over Assakrem, Algeria, we observed strong similarities between SCIAMACHY measurements and ground‐based data in deseasonalized time series. We further show long‐term SCIAMACHY xCH4 averages at high spatial resolution that provide further insight into methane variations on regional scales. The Red Basin in China exhibits, on average, the highest methane abundance worldwide, while other localized features such as the Sudd wetlands in southern Sudan can also be identified in SCIAMACHY xCH4 averages.

A multi-year methane inversion using SCIAMACHY, accounting for systematic errors using TCCON measurements

“…Artificial jumps in the retrieval due to variations in the dead and bad pixel mask are avoided in the retrieval by using only those pixels that were functioning properly throughout the whole analysed period. The instrumental damage nevertheless had an impact on the retrieval, as indicated by a marked increase in the variability of the data after November 2005 reported by Frankenberg et al (2011).…”

“…We use SCIAMACHY retrievals from the IMAPv5.5 proxy retrieval reported by Frankenberg et al (2011). The retrieved CH 4 / CO 2 ratios have been converted into XCH 4 using CarbonTracker-derived XCO 2 (Peters et al, 2007).…”

“…In the past, these techniques have most commonly been applied to ground-based measurements from global monitoring networks (Bousquet et al, 2006Houweling et al, 1999;Hein et al, 1997). In recent years, measurements from satellites have become available, such as from SCIAMACHY (Bovensmann et al, 1999;Frankenberg et al, 2005Frankenberg et al, , 2008aFrankenberg et al, , 2011Schneising et al, 2011) and more recently also from GOSAT (Yokota et al, 2009;Kuze et al, 2009;Butz et al, 2011;Schepers et al, 2012), and significant efforts have been spent to investigate their use in inverse modelling Bergamaschi et al, 2009Bergamaschi et al, , 2013Fraser et al, 2012).…”

Renewed methane increase for five years (2007–2011) observed by solar FTIR spectrometry

“…Satellite retrievals (Crevoisier et al, 2009;Frankenberg et al, 2011;Schneising et al, 2011Schneising et al, , 2012) complement these surface observations with a higher spatial coverage, but at the cost of lower precisions (≈2 %). Several studies have focused on how column observations can complement surface networks and help further reduce uncertainties associated with sources and sinks in atmospheric inversions (e.g., Olsen andRanderson, 2004 or Bergamaschi et al, 2009, and references therein).…”

WRF-Chem simulations in the Amazon region during wet and dry season transitions: evaluation of methane models and wetland inundation maps

“…Backward calculations using the STILT model indicate that most of the air at 3000-4000 m altitude in that region originates from the northwestern part of the Amazon. For this region also observations from SCIAMACHY suggest high CH 4 emissions (Frankenberg et al, 2006(Frankenberg et al, , 2011. This potential source region might not be properly represented in the flux distribution of the outer domain (d01), leading to an additional underestimation of the observations in the lower free troposphere besides vertical mixing.…”