Global HCFC-22 measurements with  MIPAS: retrieval, validation, global  distribution and its evolution over 2005–2012

Chirkov, M.; Stiller, G. P.; Laeng, A.; Kellmann, S.; von Clarmann, T.; Boone, C. D.; Elkins, J. W.; Engel, A.; Glatthor, N.; Grabowski, U.; Harth, C. M.; Kiefer, M.; Kolonjari, F.; Krummel, P. B.; Linden, A.; Lunder, C. R.; Miller, B. R.; Montzka, S. A.; Mühle, J.; O'Doherty, S.; Orphal, J.; Prinn, R. G.; Toon, G.; Vollmer, M. K.; Walker, K. A.; Weiss, R. F.; Wiegele, A.; Young, D.

doi:https://doi.org/10.5194/acp-16-3345-2016

Articles | Volume 16, issue 5

https://doi.org/10.5194/acp-16-3345-2016

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

Special issue:

Limb observations of the middle atmosphere by space- and airborne...

https://doi.org/10.5194/acp-16-3345-2016

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

Articles | Volume 16, issue 5

Research article

|

15 Mar 2016

Research article |

| 15 Mar 2016

Global HCFC-22 measurements with MIPAS: retrieval, validation, global distribution and its evolution over 2005–2012

M. Chirkov, G. P. Stiller, A. Laeng, S. Kellmann, T. von Clarmann, C. D. Boone, J. W. Elkins, A. Engel, N. Glatthor, U. Grabowski, C. M. Harth, M. Kiefer, F. Kolonjari, P. B. Krummel, A. Linden, C. R. Lunder, B. R. Miller, S. A. Montzka, J. Mühle, S. O'Doherty, J. Orphal, R. G. Prinn, G. Toon, M. K. Vollmer, K. A. Walker, R. F. Weiss, A. Wiegele, and D. Young

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Final revised paper (published on 15 Mar 2016)
Supplement to the final revised paper
Preprint (discussion started on 27 May 2015)

Interactive discussion

Status: closed

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

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RC C4691: 'Referee comment on Chirkov et al.', Anonymous Referee #1, 09 Jul 2015
RC C4828: 'Referee comment', Anonymous Referee #2, 13 Jul 2015
AC C7510: 'Final response', Gabriele Stiller, 02 Oct 2015

Peer-review completion

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

AR by Gabriele Stiller on behalf of the Authors (20 Nov 2015)

ED: Referee Nomination & Report Request started (03 Dec 2015) by Patricia Liebing

RR by Anonymous Referee #3 (09 Dec 2015)

Suggestions for revision or reasons for rejection

General Comments

The paper of Chirkov et al. presents HCFC-22 measurements from Envisat MIPAS. It shows validation with ACE-FTS, cryosampler, balloon interferometer, and surface network measurements. The global distributions and temporal evolution from 7 years of data are discussed. I found that the paper presents an interesting topic, that the scientific quality is good, and that the revised manuscript is concise and clearly written. Hence, I would recommend the paper for publication in ACP. A few minor comments and suggestions for possible consideration in the final revision are provided below.

Specific Comments

line 118: The reference to Fischer et al. (2008) could be shifted to the other references for the MIPAS instrument (lines 112-114)? It looks a bit misplaced behind the sentence discussing the Envisat orbit.

lines 195-201 / Fig. 1: Which atmospheric conditions were used for the radiative transfer calculations (mid-latitudes, polar summer/winter, tropics)?

lines 260-263: From Fig. 3 it seems the averaging kernels at 30-50 km do not peak at the nominal altitudes, but a few kilometers below?

lines 306-310 and lines 428-432: Another option to perform a comparison considering resolution effects would be to estimate smoothing errors for the MIPAS retrieval. (However, I guess that this option is not favored in Karlsruhe.)

lines 363-364: Are the differences at the top-end of the ACE-FTS profiles possibly related to uncertainties in top-column data used for the ACE-FTS retrievals?

lines 433-445: Here it is argued that a sampling radius of 1000 km and a coincidence time of +/- 24 hours are fine for the MIPAS / cryosampler comparison (based on findings from other work). However, this seems to contradict to some extent the statement that atmospheric variability within 500 km radius could contribute to differences between MIPAS and ACE-FTS (lines 336-338 and 356-358)?

lines 478-480: The retrieved profiles have even coarser vertical resolution (up to 10 km from Fig. 2) than the width of the field of view.

Fig. 10: Perhaps mention in the caption or another place which altitude coordinate is used (geometric, log-pressure)?

Section 5.1: The polar maximum at 25-30 km in austral summer is another prominent feature in the zonal mean cross-sections, which is not discussed in this section, it seems?

Technical Corrections

line 1084: "the reference" -> "reference" (?)

line 1113: remove white space before "decade"

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RR by Anonymous Referee #1 (16 Dec 2015)

Suggestions for revision or reasons for rejection

There are improvements to this manuscript and there is valuable content that should be published. The most useful parts of the paper are validation, the comparison with ACE, discussion of the high HCFC22 values filling the subtropics at 16 km and how it affects zonal means (Figs. 10-12), the global distributions and temporal evolution (Fig. 13-16), and comparison with surface networks. These sections alone would make a solid paper. I recommend publishing a paper of reduced scope, but not the current version.

The primary problem with this version remains the writing. The authors’ response to my original comments on the writing placed the burden of writing issues on the journal:
‘We have tried to improve the language of the manuscript and the paper has been proofread by native English speakers. However, language editing is now routinely done by professional language editors of ACP as part of the journal publishing process. Thus, such issues should not affect the acceptance of the paper.’
The problems are beyond proofreading. The problems include syntax, odd word choice, misuse of terminology, lack of clarity, poorly organized explanations, and failure to put new findings in the abstract and summary. The writing quality is such that it does affect acceptance. This is my primary reason for not accepting the manuscript in its current form. There are also a few science issues – detailed below. Directly below are some examples of the writing problems; they are not meant as a comprehensive list.

Example of writing Issues

Section 5.5 is a single paragraph of nearly 60 lines. Poorly organized writing is a symptom of poorly organized thoughts.

The authors did not like my comment about use of the word ‘sounded’ with respect to measurements. Their response (‘In the manuscript we have never written that measurements are sounded.’) was not to search the document for the problem areas but to deny they exist. Please see line 122 (“MIPAS sounded the atmosphere…”) and lines 393 (“…is caused by difference in the air masses sounded by each instrument…”). One could say that MIPAS remotely senses the atmosphere or that it measures thermal emissions in the limb. A passive measurement (MIPAS) does not ‘sound’ the atmosphere.

An example of confusing statements is found lines 153-161. First it is stated that the retrieval uses components relevant to non-LTE, and the next sentence says those components aren’t relevant and are not used. So which way there the measurements retrieved?

Lines 602-606. So hard to extract the meaning (about description of a feature in Figs 10 and 11). After reading the paragraphs that follow, I think I understood what you were getting at. If you discussed Figure 12 (before Fig. 10 and 11) then you could more easily explain the features in Figs. 10 and 11.

Avoid subjective adverbs ‘nicely’ and ‘perfectly’.

Section 5.2, lines 684-701. There are several occurrences of the phrase ‘numerical mixing’ used to refer to the effect of taking zonally asymmetric features and viewing them in the zonal mean. This is not what numerical mixing means! First, there is no actual mixing going on, and second, ‘numerical mixing’ is a widely used expression that refers to subgrid scale mixing in models. Similarly, the phrase ‘tropical pipe’ is erroneously used in the discussion of vertical transport in the tropical troposphere. The ‘tropical pipe’ refers to the isolation of the tropical stratosphere.

Line 690. Wave activity does affect the polar latitudes but the waves originate in the midlatitudes. They are not referred to as polar stratospheric waves.

Line 718. While the QBO has phases, the Brewer Dobson circulation does not. It has a seasonal cycle.

Line 802. The ‘semi-annual’ variation in northern midlats at 30 km. What variation is this? The SAO was previously mentioned, are you implying that’s what you see here? The SAO is a tropical upper stratospheric phenomenon and has a very weak effect outside the tropics at this altitude.

Line 920. “This reason is roughly this.” Try phrases such as ‘this can be explained by…’ or just delete.

The authors’ response stated that they had 3 new findings in this paper:
“The fact that the mixing of monsoon air into the tropics is instantaneous and not restricted to the time when the monsoon breaks down is to our best knowledge a new finding.
The fact that the temporal development of HCFC-22 in the stratosphere cannot be explained by the trends measured at the surface and the known age of air induced time lag is also a new finding.
The fact that Asian HCFC-22 emission have become the major source of global upper tropospheric HCFC-22 has been plausible but our data are to our best knowledge the first empirical evidence in support of this hypothesis.”
If you have new findings they belong in the abstract and in the summary, not buried in the paper. They don’t appear in the abstract and only 1 appears in the summary.

Science issues

Fig. 6. While I do see two difference colors of points, I do not see that they clearly fall into two clusters with respect to bias. The differences are small.
I agree that Section 4.3 (comparison with MkIV) has some value in the validation exercise, but Section 4.2 does not. The authors’ justification is that the cryosampler comparisons with other MIPAS trace gases are published therefore this comparison should be too. The papers referenced are in fact not published but are under review. The criteria used for the cryosampler data comparison (1000 km co-location) is too broad to be of use. This problem is demonstrated by the near total lack of agreement shown in Fig. 8. This section adds no value to the validation.

(You might be able to use the cryosampler data and avoid the co-location problem by comparing the tracer-tracer correlations found in MIPAS and the cryosampler. The Eckert and Laeng manuscripts use CFC11, CFC12, and CH4 observations, yes? If a goal of these comparisons is to (line 568) identify a bias due to spectroscopic information, you might be able to use the CFC11 & HCFC22 (or CH4 and HFC22) correlations for each instrument to show the bias.)

Table 3 trend comparisons. The surface growth rate of HCFC22 was fairly constant from 1992-2005 then increased. See http://www.esrl.noaa.gov/gmd/hats/graphs/graphs.html. Stratospheric air is typically between 2 and 5 years age. Because of this you cannot expect that a MIPAS trend between 2005-2012 will be the same as trends published from any stratospheric date pre-2007. Also, given the unknown bias (as reported in this paper), a trend of 6.15 +/- 0.24 (for example) shows at least 1 too many significant digits.

Section 5.5. ‘unexplained trends’. Consider these three facts in the context of the claim that this 7 year data set shows ‘an unambiguous sign that the circulation must have changed over the MIPAS period.’ 1. The changes in stratospheric HCFC22 from 2005-2012 are dominated by large increases in emissions. 2. You have measurements that you think are not biased, although you report there are biases at some altitudes with respect to other measurements. In fact, you aren’t sure of the accuracy of these measurements. 3. Studies of mean age using much longer data sets and a more careful assessment of the uncertainties find no indication of a change in stratospheric circulation (except a very slow one in the lowermost stratosphere) (Boenisch et al, ACP 2011, Engel et al., Nature 2009). Regardless of the fit you get to the time series, it is not credible that a 7 year time series of a rapidly growing trace gas could identify a change in the stratospheric circulation. It is extremely unlikely that your method is accounting for all processes affecting stratospheric variability, for the actual growth rates during this period, and that what remains must be an indication of circulation change.

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ED: Reconsider after major revisions (21 Dec 2015) by Patricia Liebing

AR by Gabriele Stiller on behalf of the Authors (29 Jan 2016) Author's response Manuscript

ED: Reconsider after minor revisions (Editor review) (08 Feb 2016) by Patricia Liebing

AR by Gabriele Stiller on behalf of the Authors (25 Feb 2016) Author's response Manuscript

ED: Publish as is (01 Mar 2016) by Patricia Liebing

AR by Gabriele Stiller on behalf of the Authors (02 Mar 2016) Author's response Manuscript

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Short summary

HCFC-22 global distributions from MIPAS measurements for 2005 to 2012 are presented. Tropospheric trends are in good agreement with ground-based observations. A layer of enhanced HCFC-22 in the upper tropospheric tropics and northern subtropics is identified to come from Asian sources uplifted in the Asian monsoon. Stratospheric distributions provide show seasonal, semi-annual, and QBO-related variations. Hemispheric asymmetries of trends hint towards a change in the stratospheric circulation.