Resolving the mesospheric nighttime 4.3&thinsp;µm emission puzzle: comparison of the CO2(ν3) and OH(ν) emission models

Panka, Peter A.; Kutepov, Alexander A.; Kalogerakis, Konstantinos S.; Janches, Diego; Russell, James M.; Rezac, Ladislav; Feofilov, Artem G.; Mlynczak, Martin G.; Yiğit, Erdal

doi:https://doi.org/10.5194/acp-17-9751-2017

Articles | Volume 17, issue 16

https://doi.org/10.5194/acp-17-9751-2017

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

https://doi.org/10.5194/acp-17-9751-2017

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

Articles | Volume 17, issue 16

Research article

|

18 Aug 2017

Research article |

| 18 Aug 2017

Resolving the mesospheric nighttime 4.3 µm emission puzzle: comparison of the CO₂(ν₃) and OH(ν) emission models

Peter A. Panka, Alexander A. Kutepov, Konstantinos S. Kalogerakis, Diego Janches, James M. Russell, Ladislav Rezac, Artem G. Feofilov, Martin G. Mlynczak, and Erdal Yiğit

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Final revised paper (published on 18 Aug 2017)
Preprint (discussion started on 22 Nov 2016)

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

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RC1: 'Review of "Resolving the mesospheric nighttime 4.3 μm emission puzzle: New model calculations improve agreement with SABER observations"', Anonymous Referee #2, 19 Dec 2016
- AC2: 'Final Response', Alexander Kutepov, 10 Mar 2017
RC2: 'Referee comments', Anonymous Referee #3, 20 Dec 2016
- AC3: 'Final Response', Alexander Kutepov, 10 Mar 2017

Peer-review completion

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

AR by Alexander Kutepov on behalf of the Authors (10 Mar 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (13 Mar 2017) by Franz-Josef Lübken

RR by Anonymous Referee #2 (14 Mar 2017)

RR by Anonymous Referee #3 (25 Mar 2017)

Suggestions for revision or reasons for rejection

The authors have addressed my comments and suggestions but very little changes have been taken into account in the revised version, eluding the most important calculations. Also, I do not like the tone of the response, e.g. sentences like "We suggest the referee read more carefully the LP04 paper ..." or "... his/her strange way of thinking..." or "We invite the referee and his/her group to make their own research contributions, given the new knowledge" are completely out of place and should be omitted. That said, I have tried to be as objective as possible.

I think the paper deserves to be published. I am making the less possible comments and are divided in: a) essentials (without which I would not recommend the publication) and b) important (highly recommendable). I also include a comment on the authors' comment at the end that do not affect the manuscript but, since this report will be public, I feel I should reply.

One of the major points comes from the interpretation of the sentence in LP04 of
“...We have investigated the SABER 4.3 µm radiances with the help of a non-LTE radiative transfer model for CO2 and found that the large radiances can be explained by a fast and efficient energy transfer rate from OH(v) to N2(1) to CO2(v3), whereby, on average, 2.8–3 N2(1) vibrational quanta are excited after quenching of one OH(v) molecule."
We may question if this mechanism is realistic or not but it is a mechanism and LP04 were able to reproduce the radiances for essentially all conditions (e.g. for 4 orbits of 4 days covering equinox and solstice (Figs. 12-14)) within +/-20%, that is, equally or better than with the new mechanism. True that so far there is no evidence of such a "direct" energy transfer process and this is why this manuscript is relevant, because it gives a plausible "indirect" way of such an energy transfer, even though the actual reaction rates have not been measured (only estimated) and the efficiency of OH(v) to O(1D) has not been measured either. Hence, I do appreciate this qualitative new mechanism. That is why I suggested to focus (title, abstract, etc.) on the new pathway more than on if it is able to reproduce better or not the measured SABER CO2 4.3 µm radiances. Then, my comments:

1) Title: (important). I would still recommend changing the part "New model calculations improve agreement with SABER observations".

2) Abstract (important): If with the "previous study" the authors refer to "Kumer et al." it is correct. However if to LP04, it is also correct but not complete (see above). My recommendation would be to give the whole story not only part of it.

3) Motivation of the work (clarification, not relevant for the manuscript). I tried to say that this work is important itself and does not need the additional justification of retrieving CO2 at night. Of course, in no way I meant to discourage the authors in pursuing such research.

4) (Essential). Since there have been already two papers dealing with this new mechanism (Sharma et al. (2015) and Kalogerakis et al. (2016)), I think this work should make the most accurate and consistent calculations as possible, making use of all available SABER data in a consistent and proper way. That it, in my opinion is not valid the argument that the purpose of this work is to make "estimates" and further work will be done later. Hence:

4a) They should use the retrieved CO2 from SABER (contrary to their reply, CO2 is publically available, (ftp://saber.gats-inc.com/Version2_0/Level2C/) and two of the co-authors are co-authors of the CO2 retrieval papers (Rezac et al., 2015a,b).
4b) My previous major comment on the OH SABER radiances (see below) has not been addressed adequately.
"As the new proposed mechanism affects also to the population of OH(v) and the emissions from these levels were measured by SABER in two different channels, I think it is essential that the authors demonstrate that the new OH(v) model explain very well the measured SABER OH radiances, as LP04 did. Thus, figures for different conditions with the SABER observations and modelled radiances for the two OH SABER channels should be presented in this work."

Thus, their replies of: "... but this is clearly out of the scope of this report."
or "The goal of our study was to estimate, ..."
I think it is crucial for this manuscript (not report), and I think it should be something more than an estimate, the title of the work reads "New model calculations improve agreement with SABER observations"

5) (Essential, in the same line as point 4). Atomic oxygen is key for the new excitation mechanism, therefore all models inputs and SABER radiances should be consistent. Thus, my previous point on this topic has not been adequately addressed. Taking from my previous report:
"About the O(3P) abundance and the OH(v) model, the authors state that they used the O(3P) retrieved from SABER measurements. The SABER O(3P) is derived from the SABER OH radiances but a photochemical OH(v) model is required for such inversion (Mlynczak et al., 2013)."

The authors should use the same photochemical OH(v) model or prove (with calculations and figures) that they are consistent.
Further on this topic, several works have shown that SABER atomic oxygen might be overestimated in a ~30%. It would very important to comment, how would this affect to the simulations of SABER CO2 4.3 µm nighttime radiances with this new mechanism?

6) Sec. 3.2 and Fig. 2 (Essential). I cannot see the reasoning of why using only the partial result of LP04. Do the authors want to validate their model? I see a high risk to misleading the reader as giving the impression that LP04 were not able to explain the SABER radiances when they did (see Figs. 10 and 11 in LP04). I strongly recommend to either show the two LP04 simulations or none.

7) (Essential) About the OH densities.
If the authors calculate OH(v) (does this include also v=0?) from SABER O3 and H, why they need OH (ground state? or total (i.e. OH(v) including v=0) from WACCM? If this is important, my previous argument whereby WACCM should sub-estimate OH still applies.
As mentioned above, the authors should use a consistent model and inputs for all quantities.

8) (important) Conclusions. As mentioned at the beginning I would focus more on the mechanism itself (find the way to transfer so much energy from OH(v) to N2(v) rather than on the "improve agreement" of the SABER radiances.
I do not fully agree with your statement that "(b) everything else that follows in our conclusions is rather measured ..." You need to make "estimates" of key parameters as how much energy is transferred from OH(v) to O(1D), both on the collisional rates and their temperature dependences.

I also do not fully agree either about the advantage of this work over previous work in the sense of making more viable the retrieval of nighttime CO2. True that the physics is known better but this is not superior to the energy efficiency factor derived by LP04 in reproducing the SABER 4.3 µm radiances. After all the two studies agree on that all energy comes from OH(v) and this is measured by SABER, so I cannot see much the advantage of using an "indirectly" derived atomic oxygen (derived from a model with potential uncertainties and that should be consistent with that used in the excitation of O(1D)=>N2(v)) or an empirical energy transfer efficiency.

Just one clarification to your statement:

• LP04 also showed that f=~3 (possible multi-quantum process, but mechanism is not explained) removes about 40% of differences for some selected scans studied. In our very extensive study we found that these differences can reach as high as 80%. Following the LP04 logic it would  require f=6 and higher to remove these differences, which is absolutely unrealistic. In other words, LP04 quantified the energy transfer efficiency that would be required for model calculations and observations to agree (for some limited set of scans), but no detailed mechanism was described, let alone validated by referring to theoretical or experimental investigations.

This is not fully true. LP04 showed, not only for some limited scans but for 4 orbits of 4 different days covering equinox and solstice conditions, that SABER measurement with f=2.8-3 could be reproduced within +/-20% (see Figs. 12-14). I would not be surprised to need larger f-values for the polar regions, where auroral excitation is prone and frequent. Also, if you analysed so many data, it would be very useful to the reader to show more than just only 2 days (Fig. 3).

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ED: Reconsider after major revisions (27 Mar 2017) by Franz-Josef Lübken

AR by Alexander Kutepov on behalf of the Authors (28 May 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (29 May 2017) by Franz-Josef Lübken

RR by Anonymous Referee #2 (01 Jun 2017)

Suggestions for revision or reasons for rejection

The revised manuscript includes important new analysis relevant to the topic. However, I'm puzzled about the authors' reply to Reviewer#3 regarding the focus of the paper. They say that they "removed any discussions of which model and how well it fits SABER measurements" , dealing now "only with the comparison of various model calculations using WACCM self-consistent inputs of all atmospheric parameters". But then the new title reads "...:Comparison of the CO2(v3) and OH(v) emission models with space and ground based observations". Further, they conclude, e.g., that the new indirect channel provides significant 4.3 um emission enhancement strong enough to *FIT* SABER radiances. This seems not consistent to me with their statement in their reply.

If the focus of the paper was limited to an intercomparison of various models then, in consequence, any comparison to observations should be excluded and the manuscript title and some parts of the manuscript need to be rewritten. In this case, it would be most appropriate to use the (OH-N2 3Q) & (OH-O2 1Q) & R7 model as reference in the comparisons of simulated 4.3 um emissions because its capacity to reproduce SABER observations (4.3, 2.0, and 1.6 um) in a self-consistent manner has been demonstrated in a previous study.

However, If they aim at evaluating the various models with observations (as suggested by the present title) it is absolutely necessary to also demonstrate that model inputs and intermediate results are consistent with the measurements. In particular, it then needs to be demonstrated that modeled ABSOLUTE OH* densities are consistent with SABER 1.6 and 2.0 um measurements. This was already requested by both reviewers in the previous iteration. However, the authors now show RELATIVE populations or VER ratios in comparison with observations. This is a very interesting additional diagnostics, however, it does not allow to judge if one or the other model provides a better description of energy transfer from OH(v>4) to CO2 because the amount of available excited OH is not constrained. In other words, good agreement of modeled and 4.3 um emissions could also be achieved by a combination of a wrong energy transfer mechanism in combination with wrong OH* densities.

This is a major concern, however, it can be easily addressed, either by some minor changes to the text (first case) or by inclusion of an additional row in Fig 3 showing observed and modeled 1.6+2.0 um ABSOLUTE VERs (second case). If in the latter case disagreement between modeled and observed VERs is obtained, a scaling of the WACCM [H]*[O3] and consequently [O] (because of chemical equilibrium) could be applied in order to achieve agreement.

Minor comments:

p5 l19-21: The use of pT from WACCM (instead from SABER as in the previous version) could introduce additional uncertainties in the comparison of modeled and observed 4.3 um emissions, which should be discussed. For instance, it is likely that the pronounced differences of both models below 75 km compared to the measurements in Fig 3 (upper panel d) are related to a temperature mismatch of WACCM. Note that, despite of being self-consistent, WACCM output does not necessarily reflect the actual atmospheric conditions of a given measurement location and time because the model is free-running in the mesosphere even in the SD mode. Real and modeled meteorology can thus be quite different. It is also not clear from the provided references what kind of WACCM simulation has been used. The Marsh et al. reference points to a free-running simulation while the Solomon et al reference points to a SD simulation, however, only for the year 2011.

p7 l9-11: There seems to be a misunderstanding of what is stated in Lopez-Puertas et al. regarding the treatment of R6 as multi- or single quantum process. The latter authors adjusted a reference OH_ref(v,z) profile that has been modeled with different implementations of R6 to the observed 1.6 and 2.0 um radiances and used then the adjusted OH(v,z) profile to simulate 4.3 um emissions. Their statement refers to the fact that changes in the vibrational distribution within v=1-5 (used to adjust the 1.6 um measurements) and that within v=6-9 (used to adjust the 2.0 um measurements), caused by the different implementations of R6, had little impact on the simulated 4.3 emission. It is evident that there would have been a significant impact if the OH(v=1-5) and OH(v=6-9) were not adjusted to the SABER 1.6 and 2.0 um radiances. Therefore, the sentence on l9-11 should be removed in order to avoid confusion.

typos:

p6 l27 kelvin -> Kelvin

p7 l 33 read ->red

p9 l32 ths -> this

p10 l20 ration -> ratio

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ED: Reconsider after minor revisions (Editor review) (01 Jun 2017) by Franz-Josef Lübken

AR by Alexander Kutepov on behalf of the Authors (10 Jun 2017) Author's response Manuscript

ED: Publish as is (19 Jun 2017) by Franz-Josef Lübken

AR by Alexander Kutepov on behalf of the Authors (27 Jun 2017) Manuscript

Short summary

Recently, theoretical and laboratory studies have suggested an additional nighttime channel of transfer of vibrational energy of OH molecules to CO₂ in the mesosphere and lower thermosphere (MLT). We show that new mechanism brings modelled 4.3 μm emissions very close to the SABER/TIMED measurements. This renders new opportunities for the application of the CO₂ 4.3 μm observations in the study of the energetics and dynamics of the nighttime MLT.

Resolving the mesospheric nighttime 4.3 µm emission puzzle: comparison of the CO2(ν3) and OH(ν) emission models

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Resolving the mesospheric nighttime 4.3 µm emission puzzle: comparison of the CO₂(ν₃) and OH(ν) emission models