Satellite chartography of atmospheric methane from SCIAMACHY on board ENVISAT: Analysis of the years 2003 and 2004

Abstract

[1] The UV/Vis/near infrared spectrometer SCIAMACHY on board the European ENVISAT satellite enables total column retrieval of atmospheric methane with high sensitivity to the lower troposphere. The vertical column density of methane is converted to column averaged mixing ratio by using carbon dioxide retrievals as proxy for the probed atmospheric column. For this purpose, we apply concurrent total column measurements of CO 2 in combination with modeled column-averaged CO 2 mixing ratios. Possible systematic errors are discussed in detail while the precision error is 1.8% on average. This paper focuses on methane retrievals from January 2003 through December 2004. The measurements with global coverage over continents are compared with model results from the chemistry-transport model TM4. In the retrievals, the north-south gradient as well as regions with enhanced methane levels can be clearly identified. The highest abundances are found in the Red Basin of China, followed by northern South America, the Gangetic plains of India and central parts of Africa. Especially the abundances in northern South America and the Red Basin are generally higher than modeled. Further, we present the seasonal variations within the investigated time period. Peak values in Asia due to rice emissions are observed from August through October. We expand earlier investigations that suggest underestimated emissions in the tropics. It is shown that these underestimations show a seasonal behavior that peaks from August through December. The global measurements may be used for inverse modeling and are thus an important step towards better quantification of the methane budget.

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.…”

Sensitivity of wetland methane emissions to model assumptions: application and model testing against site observations

“…In addition, the spatial distribution of methane emissions from wetlands is still unclear. For instance, some recent studies suggest that tropical regions (20 N-30 S) release more than 60 % of the total wetland emissions (Bergamaschi et al, 2007;Chen and Prinn, 2006;Frankenberg et al, 2006), whereas other studies argue that northern wetlands contribute as much as 60 % of the total emissions (Matthews and Fung, 1987). For tropical regions, methane emissions are highly uncertain because (1) tropical wetlands have a large area that fluctuates seasonally (Aselmann and Crutzen, 1989;Matthews and Fung, 1987;Page et al, 2011) and (2) methane fluxes vary significantly across different wetland types (Nahlik and Mitsch, 2011).…”

The global methane budget 2000–2012

“…Different retrievals of methane based on TANSO-FTS/GOSAT products are made available to the community Schepers et al, 2012;Parker et al, 2011) based on two retrieval approaches: proxy and full physics. The proxy method retrieves the ratio of methane column (XCH 4 ) and carbon dioxide column (XCO 2 ), from which XCH 4 is derived after multiplication with transport model-derived XCO 2 Peters et al, 2007;Frankenberg et al, 2006). It intends mostly to remove biases due to light scattering on clouds and aerosols and is highly efficient owing to the small spectral distance between CO 2 and CH 4 sunlight absorption bands (1.65 µm for CH 4 and 1.60 µm for CO 2 ).…”