Seasonal variability of stratospheric methane: implications for constraining tropospheric methane budgets using total column observations

Saad, Katherine M.; Wunch, Debra; Deutscher, Nicholas M.; Griffith, David W. T.; Hase, Frank; De Mazière, Martine; Notholt, Justus; Pollard, David F.; Roehl, Coleen M.; Schneider, Matthias; Sussmann, Ralf; Warneke, Thorsten; Wennberg, Paul O.

doi:https://doi.org/10.5194/acp-16-14003-2016

Articles | Volume 16, issue 21

Atmos. Chem. Phys., 16, 14003–14024, 2016

https://doi.org/10.5194/acp-16-14003-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Atmos. Chem. Phys., 16, 14003–14024, 2016

https://doi.org/10.5194/acp-16-14003-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 16, issue 21

Research article 11 Nov 2016

Research article | 11 Nov 2016

Seasonal variability of stratospheric methane: implications for constraining tropospheric methane budgets using total column observations

Katherine M. Saad et al.

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Final revised paper (published on 11 Nov 2016)
Preprint (discussion started on 10 May 2016)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of the paper by Saad et al. entitled Seasonal Variability of Stratospheric Methane: Implications for Constraining Tropospheric Methane Budgets Using Total Column Observations', Anonymous Referee #2, 07 Jun 2016
- AC1: 'Author Response to Referee #2, 'Review of the paper by Saad et al. entitled Seasonal Variability of Stratospheric Methane: Implications for Constraining Tropospheric Methane Budgets Using Total Column Observations'', Katherine Saad, 18 Aug 2016
RC2: 'Significant concerns about methodology and analysis', Anonymous Referee #3, 11 Jun 2016
- AC2: 'Author Response to Referee #3, 'Significant concerns about methodology and analysis'', Katherine Saad, 18 Aug 2016

Peer-review completion

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

AR by Katherine Saad on behalf of the Authors (18 Aug 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (02 Sep 2016) by Patrick Jöckel

RR by Anonymous Referee #3 (13 Oct 2016)

Suggestions for revision or reasons for rejection

The authors have responded well to the requests and criticisms of the reviewers. I have only a few very minor comments still, as outlined below. Then I would consider it appropriate for publication in ACP.

P 2, L29-33: I would rephrase the characterization of the Stephens et al. (2007) findings. Saying that the NH sink and tropical source were found to be overestimated "when constraining models with aircraft CO2 profiles" really makes it sound as if the aircraft profiles were assimilated, which isn't the case.

P3, L13: These forward model dependencies of CH4 concentrations *on* vertical transport

P3, L23: emissions -> emission OR emissions fluxes -> emissions OR emissions fluxes -> fluxes

P6, L7-11: Both reviewers commented on the oddness of this approach for deriving pseudo-aseasonal fluxes, which you explained as being due to a technical limitation of the model setup. Please include this justification here as well, and not only in the Conclusions. Perhaps you could refer to Figure 13 in the appendix as well.

P6, L12-15: Reads a bit awkwardly and as a result is a bit unclear. Perhaps break it into two sentences, or rewrite in some way.

P8, L5: in the both the base and -> in both the base and

P12, Figure 7 caption: Reunion is not in the Northern Hemisphere, which is implied here.

P14, L11-12: "The model’s stratospheric response to emissions perturbations differ from that of the troposphere and are subject to different transport and loss errors." -> "The model’s stratospheric response to emission perturbations differs from that of the troposphere and is subject to different transport and loss errors."

P15: in text on Figure 9, change "Emissions Seasonality" to either "Emissions' Seasonality" or "Emission Seasonality"

P15, L2: emissions errors -> emission errors OR emissions' errors

P15, L5-6: "These posterior emissions are scaled for each sector according to their a priori fraction of total emissions in each grid box." Well, it depends a bit on the inversion set-up. Not every system does it quite like this, it depends also on the a prior uncertainties assigned to each sector/process. I don't disagree with the general conclusions, but if you're going to describe a specific inversion approach, please reference it as such. It is possible to not specify the seasonal cycle in the prior, but have it driven by the data alone.

P 15: "derived by calculating the total emissions resulting from an increase of 1 ppb of CH4 in each tropospheric column and scaling". I better understood what you did after reading the response to my comment. Please integrate this information into the manuscript so that other readers may also benefit from this clarification (explaining, for instance, that transport is not considered, which is a critical limitation of the approach). And please, reword this sentence to say "the total emissions required to produce an increase of 1 ppb..."

P17, L35: scaled -> scales

P21, L6: wrong style of reference to Wunch et al. (2015)

P23, L3: as reference -> for reference

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ED: Reconsider after minor revisions (Editor review) (14 Oct 2016) by Patrick Jöckel

AR by Katherine Saad on behalf of the Authors (24 Oct 2016) Author's response Manuscript

ED: Publish as is (25 Oct 2016) by Patrick Jöckel

Short summary

Current approaches to constrain the global methane budget assimilate total column measurements into models, but model biases can impact results. We use tropospheric methane columns to evaluate model transport errors and identify a seasonal time lag in the Northern Hemisphere troposphere masked by stratospheric compensating effects. We find systematic biases in the stratosphere will alias into model-derived emissions estimates, especially those in the high Northern latitudes that vary seasonally.