Abstract
Abstract. The ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) solar occultation instrument that was launched onboard the Canadian SCISAT-1 satellite in August 2003 is measuring vertical profiles from the upper troposphere to the lower mesosphere for a large number of atmospheric constituents. Methane is one of the key species. The version v2.2 data of the ACE-FTS CH4 data have been compared to correlative satellite, balloon-borne and ground-based Fourier transform infrared remote sensing data to assess their quality. The comparison results indicate that the accuracy of the data is within 10% in the upper troposphere – lower stratosphere, and within 25% in the middle and higher stratosphere up to the lower mesosphere (<60 km). The observed differences are generally consistent with reported systematic uncertainties. ACE-FTS is also shown to reproduce the variability of methane in the stratosphere and lower mesosphere.
Highlights
Methane (CH4) is the most abundant organic trace gas in the atmosphere
We have year-round comparisons with three ground-based stations. The results of these comparisons indicate that the Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) CH4 volume mixing ratio (VMR) profiles are biased negative with respect to Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) in the 8 to 20 km www.atmos-chem-phys.net/8/2421/2008/
The comparisons with MIPAS and g-b Fourier transform infrared (FTIR) seem to be consistent with the observation from Payan et al (2007), mentioned in Sect. 5, that MIPAS has a high bias in this altitude range of the order of 5 to 20%
Summary
Methane (CH4) is the most abundant organic trace gas in the atmosphere. It is the only atmospheric organic compound that has a sufficiently long lifetime (of the order of 8 to 10 years) to be transported from the troposphere to the stratosphere. Available observations of CH4 include the in situ surface networks, in particular, the NOAA/ESRL Global Monitoring Network (http://www.esrl.noaa.gov/gmd/), and the ground-based infrared remote sensing instruments, e.g., in the framework of the Network for Detection of Atmospheric Composition Change (NDACC, http://www.ndacc.org; formerly called NDSC, for Network for the Detection of Stratospheric Change), that have provided long-term systematic high-quality measurements since the early eighties The former ones provide only local surface data. High vertical resolution profile measurements in the stratosphere and mesosphere, sometimes down to the upper troposphere, have been obtained using satellite-borne limb sounding infrared spectral instruments Among such earlier satellite experiments is the Atmospheric Trace Molecule Spectroscopy experiment (ATMOS). The ACE-FTS CH4 data set will constitute a very valuable extension of the time series made up of the ATMOS, HALOE and MIPAS data, starting in 1985, covering more than 20 years of high vertical resolution methane distributions from the upper troposphere to the mesosphere on a global scale
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