
^{1}IMKIFU, Forschungszentrum Karlsruhe, GarmischPartenkirchen, Germany ^{2}Institute of Environmental Physics (iup), University of Bremen FB1, Bremen, Germany Abstract. Methane totalvertical column retrievals from groundbased solar FTIR measurements at the Permanent GroundTruthing Station Zugspitze (47.42° N, 10.98° E, 2964m a.s.l.), Germany are used to validate column averaged methane retrieved from ENVISAT/SCIAMACHY spectra by WFMDOAS (WFMD) version 0.4 and 0.41 for 153 days in 2003. Smoothing errors are estimated to be below 0.10% for FTIR and 0.14% for SCIAMACHYWFMD retrievals and can be neglected for the assessment of observed bias and daytodayscatter. In order to minimize the altitudedifference effect, dryair column averaged mixing ratios (XCH_{4}) have been utilized. From the FTIRtime series of XCH_{4} an atmospheric daytoday variability of 1% was found, and a sinusoidal annual cycle with a ≈1.6% amplitude. To obtain the WFMD bias, a polynomial fitted to the FTIR series was used as a reference. The result is WFMD v0.4/FTIR=1.008±0.019 and WFMD v0.41/FTIR=1.058±0.008. WFMD v0.41 was significantly improved by a timedependent bias correction. It can still not capture the natural daytoday variability, i.e., the standard deviation calculated from the dailymean values is 2.4% using averages within a 2000km radius, and 2.7% for a 1000km radius. These numbers are dominated by a residual timedependent bias in the order of 3%/month. The latter can be reduced, e.g., from 2.4% to 1.6% as shown by an empirical timedependent bias correction. Standard deviations of the daily means, calculated from the individual measurements of each day, are excluding timedependent biases, thus showing the potential precision of WFMD daily means, i.e., 0.3% for a 2000km selection radius, and 0.6% for a 1000km selection radius. Therefore, the annual cycle as well as possibly the daytoday variability could be captured under the prerequisite of further advanced timedependent bias corrections, or the use of other channels, where the icing issue is less prominent. Citation: Sussmann, R., Stremme, W., Buchwitz, M., and de Beek, R.: Validation of ENVISAT/SCIAMACHY columnar methane by solar FTIR spectrometry at the GroundTruthing Station Zugspitze, Atmos. Chem. Phys., 5, 24192429, doi:10.5194/acp524192005, 2005. 
