Revised retrieval of methane and nitrous oxide from MIPAS-ENVISAT

Zonal mean distributions of methane for MIPAS reduced resolution spectra, measured between June 5th and August 18th 2010. White areas show regions with no valid data at all. On the first panel absolute values of methane (new version) are shown, on the second panel the difference of the new data minus the old version.

Various improvements were applied to the retrieval of methane and nitrous oxide from MIPAS spectra, to help eliminate a positive bias in the lower altitudes of the profiles. We use a newer spectroscopic data-set, an improved handling of the radiometric offset and continuum absorption profiles, revised microwindows, slight changes in the retrieval constraint and a joint fit of water vapour and nitric acid. These changes lead to significantly lower mixing ratios of methane and nitrous oxide in regions where the older dat-sets measured higher values than other instruments and surface measurements.