Rethinking Craig and Gordon's approach to modeling  isotopic compositions of marine boundary layer vapor

Feng, Xiahong; Posmentier, Eric S.; Sonder, Leslie J.; Fan, Naixin

doi:https://doi.org/10.5194/acp-19-4005-2019

Articles | Volume 19, issue 6

https://doi.org/10.5194/acp-19-4005-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-19-4005-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 19, issue 6

Research article

|

29 Mar 2019

Research article |

| 29 Mar 2019

Rethinking Craig and Gordon's approach to modeling isotopic compositions of marine boundary layer vapor

Xiahong Feng, Eric S. Posmentier, Leslie J. Sonder, and Naixin Fan

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Final revised paper (published on 29 Mar 2019)
Supplement to the final revised paper
Preprint (discussion started on 11 Sep 2018)
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Interactive discussion

Status: closed

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

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AC1: 'Comment from the authors regarding Eqn. 16', Xiahong Feng, 25 Oct 2018
RC1: 'Evaluation', Anonymous Referee #1, 29 Oct 2018
RC2: 'Review of Beyond Craig and Gordon: A model of water vapor isotopologues in the marine boundary layer', Anonymous Referee #2, 09 Dec 2018

Peer-review completion

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

AR by Xiahong Feng on behalf of the Authors (02 Jan 2019) Manuscript

ED: Referee Nomination & Report Request started (07 Jan 2019) by Thomas Röckmann

RR by Anonymous Referee #1 (10 Jan 2019)

RR by Anonymous Referee #2 (04 Feb 2019)

Suggestions for revision or reasons for rejection

Second review of manuscript: Beyond Craig and Gordon: A model of water vapor isotopologues in the marine boundary layer by Xiahong Feng et al.

In my first review I have stressed the need for the authors to demonstrate the usefulness of their new model. I have suggested that the authors should show how they can use water isotope observations together with their new parameterization to give new insight into processes of the atmospheric hydrological cycle.

The authors argue in their response that the usefulness and relevance is already documented in the manuscript.

For example, Feng et al. argue that the usefulness of the model can be seen by their Figure 4, which shows how water isotopes in the marine boundary layer can be explained by three processes: Equilibrium isotopic fractionation, kinetic isotopic fractionation, and mixing of the boundary layer vapor with vapor subsiding from the upper atmosphere. While it is a correct description that Figure 4 depicts, this is not new knowledge nor is it a new modelling result. Many recent papers have shown similar results by different types of improvements to the Craig and Gordon model.

I guess the future use of this model will prove me wrong with respect to its usefulness and relevance.

In my first review of this manuscript I invited the authors to give direct examples of research questions, which could be solved using their new model. The authors give many examples of type of problems that their model can be used for, but I do not find any specific research questions, which are answered using their model development in this manuscript. I would argue that a new model such as the one presented should at least be used together with observations for solving one research question.

I argued in my first review that the authors were overselling their manuscript by using the title Beyond Craig and Gordon… Unfortunately, the authors do not seem to agree with me on this either. Why not then simply call it for what it is 'A model of water vapor isotopologues in the marine boundary layer'?

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ED: Publish subject to minor revisions (review by editor) (05 Feb 2019) by Thomas Röckmann

Dear authors,
the revised version of your manuscript has been evaluated again by the two referees who also evaluated the original version. One referee is satisfied with the changes. The second referee still considers that the additional value of the model that you introduce has not been satisfactorily demonstrated, compared to other recent studies that made other kinds of adjustment to the Craig and Gordon model.
I accept the manuscript for publication in APC subject to minor revisions, but encourage you to address the two comments of the referee appropriately. I acknowledge the novel aspects of your model as described in the manuscript, but at the same time acknowledge the point of the referee that previous studies (in particular Benetti et al., 2017, who provided part of the data that you analyze) could also model these observations quite well with their model.
In revising your paper, I would like to specifically ask you to state this appropriately and discuss the differences between the approaches. In the present manuscript, the Benetti paper is cited as example of approaches that still use the closure assumption, but the fact that their model also reproduces the observations well is not adequately acknowledged. Related to the second point of the referee: It would be good to explain if there are aspects of the dataset that are modeled more accurately with your model compared to Benetti et al. This would highlight the additional value of your approach. If there is no clear quantifiable improvement, the conclusion would be that you arrive at similar conclusions, but using a modified physical representation of transport near the surface.
In this respect, I partly share the reservations by the referee that the title (and parts of the presentation) may oversell the improvements of the new approach, in particular since there are LES modeling frameworks being developed at present that may go even beyond the modifications realized in the present framework, e.g.( Wei, Z., Lee, X., & Patton, E. G. (2018). ISOLESC: A coupled isotope-LSMLES-cloud modeling system to investigate the water budget in the atmospheric boundary layer. Journal of Advances in Modeling Earth Systems, 10, 2589–2617. https://doi.org/10.1029/2018MS001381).
I would suggest that a more moderate title would be adequate, but will leave the decision to the authors.
Best regards
Thomas Röckmann

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AR by Xiahong Feng on behalf of the Authors (16 Feb 2019) Manuscript

ED: Publish as is (08 Mar 2019) by Thomas Röckmann

AR by Xiahong Feng on behalf of the Authors (18 Mar 2019)

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Short summary

We present a 1-D model to simulate H₂O isotopologues of vapor and their vertical fluxes in the first kilometer above the sea surface. The model includes two processes not in earlier Craig–Gordon isotope evaporation models: height-dependent diffusion/mixing and ascending/converging air. Calculated isotopic ratios compare well with data from seven cruises. The model explains how sea surface meteorology can affect atmospheric vapor, precipitation isotope ratios, and paleoisotope records.