Preprints
https://doi.org/10.5194/acpd-15-20395-2015
https://doi.org/10.5194/acpd-15-20395-2015
 
28 Jul 2015
28 Jul 2015
Status: this preprint has been withdrawn by the authors.

The imprint of stratospheric transport on column-averaged methane

A. Ostler1, R. Sussmann1, P. K. Patra2, P. O. Wennberg3, N. M. Deutscher4,5, D. W. T. Griffith4, T. Blumenstock6, F. Hase6, R. Kivi7, T. Warneke5, Z. Wang5, M. De Mazière8, J. Robinson9, and H. Ohyama10,a A. Ostler et al.
  • 1Karlsruhe Institute of Technology, IMK-IFU, Garmisch-Partenkirchen, Germany
  • 2Research Institute for Global Change, JAMSTEC, Yokohama, 236–0001, Japan
  • 3California Institute of Technology, Pasadena, USA
  • 4University of Wollongong, New South Wales, Wollongong, Australia
  • 5Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 6Karlsruhe Institute of Technology, IMK-ASF, Karlsruhe, Germany
  • 7Finnish Meteorological Institute, Arctic Research Center, Sodankylä, Finland
  • 8Belgian Institute for Space Aeronomy, BIRA-IASB, Brussels, Belgium
  • 9National Institute of Water and Atmospheric Research, NIWA, Omakau, New Zealand
  • 10Earth Observation Research Center, EORC, Aerospace Exploration Agency, JAXA, Tsukuba, Japan
  • anow at: Solar-Terrestrial Environment Laboratory, Nagoya University, Nagoya, Japan

Abstract. Model simulations of column-averaged methane mixing ratios (XCH4) are extensively used for inverse estimates of methane (CH4) emissions from atmospheric measurements. Our study shows that virtually all chemical transport models (CTM) used for this purpose are affected by stratospheric model-transport errors. We quantify the impact of such model transport errors on the simulation of stratospheric CH4 concentrations via an a posteriori correction method. This approach compares measurements of the mean age of air with modeled age and expresses the difference in terms of a correction to modeled stratospheric CH4 mixing ratios. We find age differences up to ~ 3 years yield to a bias in simulated CH4 of up to 250 parts per billion (ppb). Comparisons between model simulations and ground-based XCH4 observations from the Total Carbon Column Network (TCCON) reveal that stratospheric model-transport errors cause biases in XCH4 of ~ 20 ppb in the midlatitudes and ~ 27 ppb in the arctic region. Improved overall as well as seasonal model-observation agreement in XCH4 suggests that the proposed, age-of-air-based stratospheric correction is reasonable.

The latitudinal model bias in XCH4 is supposed to reduce the accuracy of inverse estimates using satellite-derived XCH4 data. Therefore, we provide an estimate of the impact of stratospheric model-transport errors in terms of CH4 flux errors. Using a one-box approximation, we show that average model errors in stratospheric transport correspond to an overestimation of CH4 emissions by ~ 40 % (~ 7 Tg yr−1) for the arctic, ~ 5 % (~ 7 Tg yr−1) for the northern, and ~ 60 % (~ 7 Tg yr−1) for the southern hemispheric mid-latitude region. We conclude that an improved modeling of stratospheric transport is highly desirable for the joint use with atmospheric XCH4 observations in atmospheric inversions.

This preprint has been withdrawn.

A. Ostler et al.

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Interactive discussion

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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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A. Ostler et al.

A. Ostler et al.

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This preprint has been withdrawn.

Short summary
We find that stratospheric model-transport errors are common for chemical transport models that are used for inverse estimates of CH4 emissions. These model-transport errors cause latitudinal as well as seasonal biases in simulated stratospheric and, hence, column-averaged CH4 mixing ratios (XCH4). Such a model bias corresponds to an overestimation of arctic and mid-latitude CH4 emissions if inversion studies do not apply an ad hoc bias correction before inverting fluxes from XCH4 observations.
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