Contributions of the troposphere and stratosphere to CH<sub>4</sub> model biases

Wang, Zhiting; Warneke, Thorsten; Deutscher, Nicholas M.; Notholt, Justus; Karstens, Ute; Saunois, Marielle; Schneider, Matthias; Sussmann, Ralf; Sembhi, Harjinder; Griffith, David W. T.; Pollard, Dave F.; Kivi, Rigel; Petri, Christof; Velazco, Voltaire A.; Ramonet, Michel; Chen, Huilin

doi:https://doi.org/10.5194/acp-17-13283-2017

Articles | Volume 17, issue 21

https://doi.org/10.5194/acp-17-13283-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-17-13283-2017

© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 17, issue 21

Research article

|

09 Nov 2017

Research article |

| 09 Nov 2017

Contributions of the troposphere and stratosphere to CH₄ model biases

Zhiting Wang, Thorsten Warneke, Nicholas M. Deutscher, Justus Notholt, Ute Karstens, Marielle Saunois, Matthias Schneider, Ralf Sussmann, Harjinder Sembhi, David W. T. Griffith, Dave F. Pollard, Rigel Kivi, Christof Petri, Voltaire A. Velazco, Michel Ramonet, and Huilin Chen

Download

Final revised paper (published on 09 Nov 2017)
Preprint (discussion started on 23 Dec 2016)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

- Printer-friendly version

- Supplement

RC1: 'referee comments', Anonymous Referee #2, 20 Jan 2017
- AC1: 'Response to referee #1', Zhiting Wang, 31 Mar 2017
RC2: 'referee comments', Anonymous Referee #1, 01 Feb 2017
- AC2: 'Response to referee #2', Zhiting Wang, 31 Mar 2017
  - AC3: 'further reply to refree #2', Zhiting Wang, 05 May 2017

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Zhiting Wang on behalf of the Authors (31 Mar 2017) Author's response Manuscript

ED: Reconsider after major revisions (12 May 2017) by Ilse Aben

AR by Zhiting Wang on behalf of the Authors (12 May 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 May 2017) by Ilse Aben

RR by Anonymous Referee #1 (28 May 2017)

ED: Reconsider after minor revisions (Editor review) (20 Jun 2017) by Ilse Aben

AR by Zhiting Wang on behalf of the Authors (10 Jul 2017) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (12 Jul 2017) by Ilse Aben

AR by Zhiting Wang on behalf of the Authors (14 Jul 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Jul 2017) by Ilse Aben

RR by Anonymous Referee #1 (21 Jul 2017)

Suggestions for revision or reasons for rejection

Following the correspondence about my review I have analyzed the whole discussion to find the origin if our misunderstanding regarding General point 2 of my review, which had to do with the impact of the scaling of the tropospheric and stratospheric sub columns that is applied.

In my opinion the discussion is confused because the authors do not distinguish between the following:

1) The contribution of the modelled tropospheric sub column to a bias in the total column averaged mixing ratio

2) A bias in the modelled tropospheric sub column averaged mixing ratio

If scaling is applied [as mentioned in the caption of figure 3] this is appropriate for 1) but not for 2). However, in the language that is used in the paper there is no distinction between 1) and 2). In many instances the language suggests 2) [e.g. in the abstract: ‘the tropospheric model biases show a latitudinal gradient for all models’], referring to numbers that are derived using the scaling method, which doesn’t apply to that case and therefore causes confusion.

Special care should be taken when comparing results of 1) to comparisons of the model with in situ data. In situ data can only represent local CH4 mixing ratios. If they are compared to 2) this is problematic already because of the vertical gradient in the troposphere as pointed out by the coauthors. However, they cannot be compared to 1).

I my original review I tried to explain this point using an example of how the mixing up of 1) and 2) could go wrong: “According to the caption of Figure 3, the tropospheric and stratospheric model biases are scaled with the corresponding contributions of the troposphere and the stratosphere to the total column air mass. However, there is a danger in doing so. Suppose that the model had a latitudinally and seasonally uniform offset in the tropospheric concentration. Then the scaling with the seasonal and latitudinal varying tropopause pressure would introduce a seasonal and latitudinal variation in the bias >>here I meant in XCH4<<. In that case, when you look for varying biases within the troposphere in comparison with in situ data you wouldn’t find any. This is exactly what seems to be happening here.”
A good way (and even necessary I would say) way to analyze whether or not the troposphere has a latitudinal/seasonal bias would be to assess the bias between the model and the tropospheric columns derived from TCCON (e.g. in a way similar to what is done in Figure 3, but for tropospheric columns and therefore without scaling).

In my opinion, this manuscript can only be accepted for publication in ACP if this confusion, which is integral to the entire document, is taken care of by clearly separating between 1) and 2) in method and language. In the second iteration of my review I had marked this issue as a minor revision. However, since the authors fail to provide an appropriate solution I have changed it into major to make clear that I am against publication unless this issue is satisfactorily resolved.

Hide

ED: Reconsider after major revisions (21 Jul 2017) by Ilse Aben

AR by Zhiting Wang on behalf of the Authors (12 Sep 2017) Author's response Manuscript

ED: Publish subject to technical corrections (03 Oct 2017) by Ilse Aben

AR by Zhiting Wang on behalf of the Authors (05 Oct 2017) Author's response Manuscript

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.

Contributions of the troposphere and stratosphere to CH4 model biases

Download

Interactive discussion

Peer-review completion

Contributions of the troposphere and stratosphere to CH₄ model biases