Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

Remsberg, E. E.

doi:https://doi.org/10.5194/acp-15-3739-2015

Articles | Volume 15, issue 7

https://doi.org/10.5194/acp-15-3739-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/acp-15-3739-2015

© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 15, issue 7

Research article

|

07 Apr 2015

Research article |

| 07 Apr 2015

Methane as a diagnostic tracer of changes in the Brewer–Dobson circulation of the stratosphere

E. E. Remsberg

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Final revised paper (published on 07 Apr 2015)
Preprint (discussion started on 18 Sep 2014)

Interactive discussion

Status: closed

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

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- Supplement

RC C8932: 'Review acpd-14-24183-2014', Anonymous Referee #1, 08 Nov 2014
- AC C10387: 'Response to Anonymous Reviewer #1', Ellis Remsberg, 19 Dec 2014
RC C9398: 'Review', Anonymous Referee #2, 21 Nov 2014
- AC C10386: 'Response to Reviewer #2', Ellis Remsberg, 19 Dec 2014

Peer-review completion

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

AR by Ellis Remsberg on behalf of the Authors (15 Jan 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (31 Jan 2015) by Peter Haynes

RR by Anonymous Referee #2 (13 Feb 2015)

Suggestions for revision or reasons for rejection

I recommend the manuscript to be accepted basically as is, but have some minor comments that may require slight re-wording of a few sentences:

(Page-Line)

P2-L3/4: Prone for misunderstanding; should read "The dynamically forced circulation ...
is balanced by differential radiative heating between Equator and Pole."

P4-L10/11: Linear trend of CH4 not quite correct ...
I see that you later clarify this point (page 14); perhaps say
here that you will discuss this in detail later.

P5-L1-8: The loss function L(r,t') may also change over time. Given the
various complications, it may be useful to state that:
- to first approximation, both the path and loss function L()
can be assume stationariy, such that methane in the stratosphere
is a fraction "f" of the tropospheric methane, where "f" is a function
of latitude/height and season. (Which can be further simplified to
latitude/potential temperature outside the vortex.)
(That's used in Fueglistaler 2012).
- In the present study, deviations from this scenario are interpreted
as being indicative of changes in the age spectra G, rather than L.
I think this is the correct order for the importance of changes
in G and L, but I am actually not sure whether anyone ever has shown
how robust this is; but it seems plausible to me that the chemical
influence of changes in stratospheric composition on methane oxidation
rates (i.e. basically via changes in OH-concentrations) is small.

P5-L12: "CH_4is"

P9-L14: It may be helpful if stated explicitly that the assumption is that
the age spectrum G is invariant in pressure space if the dynamical
forcing is invariant in pressure space.

P9-L25: As in opening sentence, I think this is not quite correctly formulated;
the BD-circulation is not forced by differential heating, the differential
heating is a consequence of variations in dynamical forcing.

Additional paragraphs provided to editor: For both paragraphs, I did not understand the conclusions
stated in the last ~3 sentences; other than that I have no objection to including them in the paper.

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RR by Anonymous Referee #1 (14 Feb 2015)

ED: Reconsider after minor revisions (Editor review) (15 Feb 2015) by Peter Haynes

AR by Ellis Remsberg on behalf of the Authors (24 Feb 2015) Author's response Manuscript

ED: Publish as is (22 Mar 2015) by Peter Haynes

AR by Ellis Remsberg on behalf of the Authors (23 Mar 2015)

Short summary

Time series of the satellite-observed stratospheric tracer, CH4, are analyzed to see whether they indicate a significant trend for the hemispheric Brewer--Dobson circulation (BDC) for 1992-2005. Trends in CH4 for the lower stratosphere are generally positive and equivalent to those of the troposphere. However, the Northern Hemisphere BDC is clearly accelerated in the mid-stratosphere (20 to 7hPa). Corresponding trends for the Southern Hemisphere are smaller and less significant.