Stratospheric gravity waves in a post-limb sounder era: can GNSS-RO be used to extend the SABER QBO-driving record?

Almowafy, Marwa; Wright, Corwin J.; Hindley, Neil P.

doi:10.5194/amt-18-6393-2025

Articles | Volume 18, issue 21

https://doi.org/10.5194/amt-18-6393-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-18-6393-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 18, issue 21

Research article

|

11 Nov 2025

Research article |

| 11 Nov 2025

Stratospheric gravity waves in a post-limb sounder era: can GNSS-RO be used to extend the SABER QBO-driving record?

Marwa Almowafy, Corwin J. Wright, and Neil P. Hindley

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Final revised paper (published on 11 Nov 2025)
Preprint (discussion started on 13 Jan 2025)

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-3524', Anonymous Referee #1, 31 Jan 2025

Comments on the manuscript "Observations of stratospheric gravity waves in the tropics: can GNSS-RO extend the SABER climatological record?"
General Comment:

Gravity waves is importing in driving QBO in the tropic stratosphere due to wave-flow interactions. Previous studies have showed that GWs with shorter vertical wavelengths play more important role in driving QBO as compared to the GWs with longer vertical wavelength. The main idea of this work is to explore the influences of observational filters of different instrument on the derived GW parameters and their possible influences with QBO. However, some revisions should be performed.
Major comments:

1. The title: "can GNSS-RO extend the SABER climatological record?". The main content of this work is the effects of observational filters on the parameters of derived GWs from SABER and GNSS-RO. The title does not match the main content. Please clarify the extent and/or the aspect on which the GNSS-RO can extend the SABER climatological record.

2. Abstract: Only the purpose and method of this work are presented. It is better to present some quantitative results in the abstract.

3. Comparing the difference of Ep and vertical wavelength: the difference between those derived from SABER and GNSS-RO are compared in the manuscript. Howerver, the absolute of values of Ep and vertical wavelength derived SABER or GNSS-RO are not known, consequently, the statistical significance of the difference is unkonw. Otherwise, one may provide the percentage contributions of Ep (and vertical wavelength) on the total Ep from both SABER and GNSS-RO. Also, the statistical significance of the differences should be provided.

4. Please summarize the main similarities and differences of SABER and GNSS-RO in studying the GW-QBO interactions.
Minor comments:

1. Figure 2 caption, "the thick"-->"The tick". The ticks are unreadable in panel (c) of Figure 2 and in other contour figures (Figures 3, 5, 6, 10, 11 ).

2. L266: How to determine the upper limit of horizontal wavelength (2000 km) measured by SABER and GNSS-RO?

3. L269: Since the lower limits of vertical wavelengths are different (2 km for GNSS-RO, 4 km for SABER). For a fair comparison, the analysis to GWs to GWs with vertical wavelength shorter than 12 km. The lower limits of the vertical wavelengths of both measurements should also be mentioned.

4. L278-279: "panel (a)"-->"panel (a) of Figure 3"? "panel (b)"-->"panel (b) of Figure 3"?

5. Section 4.2: There is no description on the 2019 disruption.

6. L366: Where can I refer and how can I understand the statement "the shorter wavelengths detected by GNSS-RO are associated with a larger range of Ep compared to SABER"?

7. Conclusion: It is better to conclude the new finding(s) and/or limitations more specifically and quantitatively of this work. Other than the qualitative statements such as, "emphasizing the importance of selecting an appropriate instrument for targeted gravity wave studies", etc.

Citation: https://doi.org/10.5194/egusphere-2024-3524-RC1
- AC2:
  'Reply on RC1', Marwa Almowafy, 28 Mar 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3524/egusphere-2024-3524-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-3524-AC2
  - AC3: 'Reply on AC2', Marwa Almowafy, 30 Apr 2025
    
    The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3524/egusphere-2024-3524-AC3-supplement.pdf
    
    Citation: https://doi.org/10.5194/egusphere-2024-3524-AC3
RC2:
'Comment on egusphere-2024-3524', Anonymous Referee #2, 04 Feb 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3524/egusphere-2024-3524-RC2-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-3524-RC2
- AC1:
  'Reply on RC2', Marwa Almowafy, 28 Mar 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3524/egusphere-2024-3524-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-3524-AC1
  - AC4: 'Reply on AC1', Marwa Almowafy, 30 Apr 2025
    
    The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3524/egusphere-2024-3524-AC4-supplement.pdf
    
    Citation: https://doi.org/10.5194/egusphere-2024-3524-AC4

Peer review completion

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

AR by Marwa Almowafy on behalf of the Authors (28 Mar 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (29 Mar 2025) by Wen Yi

RR by Anonymous Referee #1 (09 Apr 2025)

Suggestions for revision or reasons for rejection

Comments on the manuscript "Observations of stratospheric gravity waves in the tropics: can GNSS-RO extend the SABER climatological record?"

General Comment:
Thanks for the responses from authors. However, as far as my knowledge, some confused issues are not resolved yet. Please see the comments below.

Major comments:
1. L9-13: "To test this ... the same results": These sentences show your purpose and main procedures. It is better to provide your main conclusions here. such as, how about the observed GWs depend on the viewing angles, the vertical and horizontal resolutions of SABER and GNSS-RO by using the same atmosphere data (high-resolution GEOS model). However, in the subsequent sentences, I think the GW Ep were calculated from the actual observations from SABER and GNSS-RO.
2. L14 and L19: Does the 1.3 Jkg-1 and 0.5 Jkg-1 are different from zero in statistical sense?
3. L15-17: "...the most significant factor in determining...", How about the quotative relation between the difference (between the results of both instruments) between the vertical resolution? Does the resolution mean the vertical step of between two consecutive sampling points.
4. The second paragraph of the Abstract: What is the conclusion of this paragraph in supporting the “interactions between GWs and the QBO” as stated in L6-9
5. The third paragraph of the Abstract: This paragraph only shows the essential rule of studying gravity waves. The question is what are the appropriate observational methods for gravity wave research of this work?
6. Please clarify the terms used in the text: resolution, sampling step, lower limit of the vertical wavelength used to derived Ep.
7. Looking through the abstract, I still cannot get the main purpose of this manuscript. In the response: As stated in the response, the main purposes are: (1) address the observational filter differences between GNSS-RO and SABER measurements, (2) given the known observational filter differences between both techniques, (3) validate the reliability of SABER observation through comparing the GW derived from both SABER and GNSS-RO. Please fulfil these purposes in the abstract since the abstract should not provide only the purpose of the work but provide a concise summary of the research purpose, methods, main results, and conclusions. After these issues are resolved, you may find a proper title.

Minor comments:
1. L100: Please provide some references of “other datasets”.
2. L118: What is the mean of “vertical resolution of ∼1 km”. It is better to say that the temperature profiles have a uncertainty or accuracy of ? K with vertical sampling step of 1 km in the stratosphere. Corresponding revisions should be made for SABER temperature (L132-133). Otherwise, if one does not consider the temperature uncertainty or accuracy, the vertical sampling stem can be arbitrary through over-sampling or down-sampling or interpolation.
3. L122-125: How about the consistency of the GNSS-RO measurements from different missions? i.e., the standard derivations of the concurrent temperature profiles measured from different missions.
4. L148: Here, the vertical resolutions may be replaced by vertical step. Please use “resolution” properly throughout the manuscript for the purpose of more readable and accurate.
5. L204-210: “excluding any with vertical wavelengths greater than 12 km”, Does this apply on both SABER and GNSS-RO data? How about the shortest vertical wavelengths of GWs derived from SABER and GNSS-RO data?
6. L223: “eastward peaks of the zonal wind”: How about the time step of zonal wind, daily or monthly? It seems that the zonal wind is on a monthly scale as seen from Figure 3. Please clarify this in the text.
7. L281-284: “The horizontal resolution” might be “the horizontal sampling step”? This leads the resolved horizontal wavelength of more than 270 km? Moreover, this is conflict to the statements in L260-264: “however, accurate measurements of the λh are difficult or impossible for GNSS-RO because the profiles are not regularly spaced”. In fact, even at the early missions of GNSS-RO, the RO profiles were not regularly spaced. Please clarify these statements.
8. L281-288: From these sentences, I get that the upper limit of the vertical wavelength is 12 km for both SABER and GNSS-RO. I guess that the lower limit of the vertical wavelengths is, receptively, 2 km for GNSS-RO and 4 km for SABER. However, the lower limit of the vertical wavelengths shown in Figure A2 is receptively, 4 km for GNSS-RO and 7 km for SABER. I confuse that what is the lower limit of the vertical wavelength, which is used to derive Ep from GNSS-RO and SABER. This is important since the Ep is dependent on the range of the vertical wavelength even for the profiles measured by same instrument. Please clarify the lower limit of the vertical wavelength, which is used to derive Ep.
9. L292: Please provide the method of get periodogram.
10. L339-346: This paragraph provides a statistical test for specific period. However, it is better to the confidence level of the statistical test. For example, the QBO is 2.4 years with 0 FAP. One can infer that the period of 2.5 years has a FAP of below 0.01, which is still a secure result. Due to the variability of QBO period from year to year, a better representation of QBO period might be a statistical distribution with center of ? months and standard deviation of ? months.
11. Section 5.1: The range of vertical wavelengths of GW, which is used to derive Ep should also be clarified.

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RR by Anonymous Referee #2 (14 Apr 2025)

ED: Reconsider after major revisions (15 Apr 2025) by Wen Yi

AR by Marwa Almowafy on behalf of the Authors (30 Apr 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (06 May 2025) by Wen Yi

RR by Anonymous Referee #1 (14 May 2025)

ED: Reconsider after major revisions (14 May 2025) by Wen Yi

AR by Marwa Almowafy on behalf of the Authors (06 Aug 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (20 Aug 2025) by Wen Yi

RR by Anonymous Referee #1 (25 Aug 2025)

ED: Publish subject to minor revisions (review by editor) (04 Sep 2025) by Wen Yi

AR by Marwa Almowafy on behalf of the Authors (13 Sep 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (22 Sep 2025) by Wen Yi

AR by Marwa Almowafy on behalf of the Authors (22 Sep 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (29 Sep 2025) by Wen Yi

AR by Marwa Almowafy on behalf of the Authors (30 Sep 2025) Manuscript

Short summary

Gravity waves (GW) influence atmospheric dynamics. One key effect is on the zonal winds in the tropics stratosphere, which drive the quasi-biennial oscillation (QBO). Satellite observations are used to study gravity waves, but each satellite is constrained by its observational limits. This study investigates how GW–QBO interactions are observed by two satellites, SABER and GNSS-RO, and examines the potential for GNSS-RO to extend the GW climatology that is carried out by SABER for 23 years.