Interpretability of negative latent heat fluxes from eddy covariance measurements in dry conditions

Paulus, Sinikka J.; Orth, Rene; Lee, Sung-Ching; Hildebrandt, Anke; Jung, Martin; Nelson, Jacob A.; El-Madany, Tarek Sebastian; Carrara, Arnaud; Moreno, Gerardo; Mauder, Matthias; Groh, Jannis; Graf, Alexander; Reichstein, Markus; Migliavacca, Mirco

doi:https://doi.org/10.5194/bg-21-2051-2024

Articles | Volume 21, issue 8

https://doi.org/10.5194/bg-21-2051-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/bg-21-2051-2024

© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 8

Research article

| Highlight paper

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25 Apr 2024

Research article | Highlight paper |

| 25 Apr 2024

Interpretability of negative latent heat fluxes from eddy covariance measurements in dry conditions

Sinikka J. Paulus, Rene Orth, Sung-Ching Lee, Anke Hildebrandt, Martin Jung, Jacob A. Nelson, Tarek Sebastian El-Madany, Arnaud Carrara, Gerardo Moreno, Matthias Mauder, Jannis Groh, Alexander Graf, Markus Reichstein, and Mirco Migliavacca

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Final revised paper (published on 25 Apr 2024)
Preprint (discussion started on 06 Nov 2023)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-2556', Anonymous Referee #1, 02 Dec 2023

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2556/egusphere-2023-2556-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2023-2556-RC1
- AC1: 'Reply on RC1', Sinikka Paulus, 01 Feb 2024
  
  The reviewer has a lengthy and detailed discussion of our manuscript, raising a number of critical points that we address in our responses and the revised version of the manuscript. Due to the volume of comments and our responses, we have provided a PDF file that reproduces each reviewer's comment, followed by our individual responses.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2556-AC1
RC2:
'Comment on egusphere-2023-2556', Anonymous Referee #2, 08 Jan 2024

My congratulations and thanks to the authors for putting together a clear and compelling case for detecting soil water vapor adsorption (SVA) using eddy covariance measurements. I found the paper easy to follow with interesting results and conclusions that were well supported.
I have only some paper specific edits to suggest and comments that need clarification (minor revisions to address before publication).
L16-17. Wouldn’t this claim about the prevalence of SVA be better supported by using the lysimeter results themselves? If so, change the text and move this above the results on how well EC does at detecting these events.
L 20. Here and in the main body I found this result on using RF to explain mismatches between the two techniques to be confusing. In the text, I thought you were using RF mainly to explain mismatches between lysimeters themselves rather than differences between Fin estimates between EC and lysimeter?
L30. Is there a citation for this being an underrepresented component of the research?
L91. “distance between the sampling height and the ground”
L100. Suggest using “forces” instead of force fields.
L108. “escape the liquid phase”
Figure 1. Great summary figure!
L71. “…integral turbulence characteristics were removed” - This wasn’t mentioned for the other site. Also, is this based on measurements of turbulent mixing strength like u*?
L277. U* = 0.01 m/s is extremely low. Is this a typo, maybe 0.1?
Figure 3. This is very compelling evidence of EC detection of negative fluxes indicating SVA. Would it also be possible to select a few multiday periods with substantial Ein and show mean diurnal plots of E for both the lysimeters and the flux tower? Just 2 or 3 of these would show whether there is strong evidence of SVA during dry periods and its magnitude relative to the daytime values. I know this is quantified later in the manuscript but this would be a way to show it visually.

L360. I don’t understand “the process is independent of climate”. It seems highly dependent on climate conditions. Please clarify.

Table 2. Could you please add the number of periods/days that the lysimeters recorded these events?

L434. Why better? Couldn't it be that the lysimeter spatial mean is biased high compared to the broader EC scale?

L484-486. I had trouble understanding this conclusion. I thought the sentences above were talking about what explains the differences between lysimeters and not between EC and lysimeters. Can you please explain and maybe rewrite this sentence?

Figure 9 . Both axes in (c) are labeled as IN.

L519-523. I think this text applies to bare soil evaporation. Evaporation from mixed plant/soil conditions as you have for the lysimeters and EC fluxes occurs differently than this in that stage 2 isn't just about diffusion-limited processes through the soil as plant transpiration is also a substantial element for this period (or at least for all but the driest conditions).

Citation: https://doi.org/10.5194/egusphere-2023-2556-RC2
- AC2: 'Reply on RC2', Sinikka Paulus, 01 Feb 2024
  
  The reviewer has a lengthy and detailed discussion of our manuscript, raising a number of critical points which we address in our responses and in the revised version of the manuscript. Due to the volume of comments and our responses, we have provided a PDF file that reproduces each reviewer's comment, followed by our individual responses.
  
  Citation: https://doi.org/10.5194/egusphere-2023-2556-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

ED: Publish subject to minor revisions (review by editor) (11 Feb 2024) by Andrew Feldman

We’ve received comments from two reviewers, both experts in this field. Both are supportive and recommend the manuscript for publication after minor revisions. After reading myself, I agree with the two reviewers that the paper is well written and interesting.

Some brief comments on the reviewer’s points: While I can see Reviewer 1’s point, I agree with the authors’ response that it is good to keep the wetter site in Germany in the analysis to show the contrast with the drier site. I also agree with the second reviewer that some more motivation and discussion of explaining the mismatch between EC and lysimeter is interesting rather than explaining the lysimeter patterns.

I also have some additional comments below to consider. Ultimately, we invite the authors to implement their revisions.

1) The condition for SVA discussed in lines 230-240 might need some more discussion. Specifically, if the soil temperature (Ts) is below the dew point, wouldn’t this be conditions for dew formation on the soil surface/pores? Therefore, SVA in the soil occurs below the dew point? Dew should form when the air temperature (or the bare soil surface Ts in this case) drops below the dew point. If I am misunderstanding, please provide some more detail on this point.

2) l and g are not defined in the caption in Fig. 1

3) Consider showing a time series to demonstrate SVA with the lysimeter and EC. Currently, while detailed, Fig. 3 and 4 are quite dense and potentially difficult for some readers to see the SVA process. It looks like Reviewer 2 requested something like this.

4) An error propagation analysis was mentioned around line 442. Please consider showing this analysis in the supplemental materials given the value it adds.

-Andrew Feldman

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AR by Sinikka Paulus on behalf of the Authors (20 Feb 2024) Author's response Author's tracked changes Manuscript

ED: Publish as is (29 Feb 2024) by Andrew Feldman

AR by Sinikka Paulus on behalf of the Authors (04 Mar 2024) Author's response Manuscript

Co-editor-in-chief

This study presents an interesting finding that, when climatic conditions are dry, the direction of soil evaporation from soil to sky can reverse where atmospheric vapor adsorbs downward into the soil. This increased soil moisture input from the atmosphere serves as a non-precipitation water source. The authors show evidence for this process with lysimeters and also demonstrate that this soil adsorption process shows up in commonly used eddy covariance measurements.