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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Dec 2016
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Contributions of the troposphere and stratosphere to CH4 model biases
Zhiting Wang1, Thorsten Warneke1, Nicholas Deutscher1,2, Justus Notholt1, Ute Karsten3, Marielle Saunois4, Mattias Schneider5, Ralf Sussmann6, Harjinder Sembhi7, Dave W. T. Griffith2, Dave F. Pollar8, Rigel Kivi9, Christof Petri1, Voltaire A. Velazco2, Michel Ramonet10, and Huilin Chen11,12 1Institute of Environmental Physics, University of Bremen, Bremen, Germany
2Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Wollongong, New South Wales, Australia
3Max Planck Institute for Biogeochemistry, Jena, Germany
4Laboratoire des Sciences du Climat et de l'Environnement, Université Paris-Saclay 91191 Gif-sur-Yvette, France
5Karlsruhe Institute of Technology, IMK-ASF, Karlsruhe, Germany
6Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
7Earth Observation Science, Department of physics and Astronomy, University of Leicester, Leicester, UK
8National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
9Finnish Meteorological Institute Arctic Research Center, FMI-ARC, Sodankylä, Finland
10Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris Saclay, 91191, Gif-Sur-Yvette, France
11Center for Isotope Research (CIO), University of Groningen, Groningen, the Netherlands
12Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA
Abstract. Inverse modeling is a useful tool to retrieve CH4 fluxes; however, evaluation of the applied chemical transport model is an important step before using the inverted emissions. For inversions using column data one concern is how well the model represents stratospheric and tropospheric CH4 respectively when assimilating total column measurements. In this study atmospheric CH4 from three inverse models is compared to FTS (Fourier Transform Spectrometry), satellite and in situ measurements. Using the FTS measurements the model biases are separated into stratospheric and tropospheric contributions. When averaged over all FTS sites the model bias amplitudes (absolute model to FTS differences) are 7.4 ± 5.1 ppb, 6.7 ± 4.8 ppb, and 8.1 ± 5.5 ppb in the troposphere for the models TM3, TM5-4DVAR, LMDz-PYVAR, respectively, and 4.3 ± 9.9 ppb, 4.7 ± 9.9 ppb, and 6.2 ± 11.2 ppb in the stratosphere. The tropospheric model biases show a latitudinal gradient for all models, however there are no clear latitudinal dependencies for stratospheric model biases visible except with the LMDz-PYVAR model. The latitudinal gradient is not present in a comparison with in situ measurements, which is attributed to the different longitudinal coverage of FTS and in situ measurements. Similarly, a latitudinal pattern exists in model biases in vertical CH4 gradients in the troposphere, which indicates vertical transports of tropospheric CH4 is not represented correctly in the models.

Citation: Wang, Z., Warneke, T., Deutscher, N., Notholt, J., Karsten, U., Saunois, M., Schneider, M., Sussmann, R., Sembhi, H., Griffith, D. W. T., Pollar, D. F., Kivi, R., Petri, C., Velazco, V. A., Ramonet, M., and Chen, H.: Contributions of the troposphere and stratosphere to CH4 model biases, Atmos. Chem. Phys. Discuss.,, in review, 2016.
Zhiting Wang et al.
Zhiting Wang et al.
Zhiting Wang et al.


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Short summary
In this paper we separate the biases of atmospheric methane models into stratospheric and tropospheric parts. It is observed in other studies that simulated total columns of atmospheric methane present a latitudinal bias compared to measurements. The latitudinal gradients are considered to be from the stratosphere. However, our results show that the latitudinal biases could come from the troposphere in two of three models evaluated in this study.
In this paper we separate the biases of atmospheric methane models into stratospheric and...