Monitoring sudden stratospheric warmings using radio occultation: a new approach demonstrated based on the 2009 event

Li, Ying; Kirchengast, Gottfried; Schwärz, Marc; Ladstädter, Florian; Yuan, Yunbin

doi:https://doi.org/10.5194/amt-14-2327-2021

Articles | Volume 14, issue 3

https://doi.org/10.5194/amt-14-2327-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/amt-14-2327-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 14, issue 3

Research article

|

26 Mar 2021

Research article |

| 26 Mar 2021

Monitoring sudden stratospheric warmings using radio occultation: a new approach demonstrated based on the 2009 event

Ying Li, Gottfried Kirchengast, Marc Schwärz, Florian Ladstädter, and Yunbin Yuan

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Final revised paper (published on 26 Mar 2021)
Preprint (discussion started on 17 Jul 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'a review report on AMT-2020-184', Anonymous Referee #3, 08 Aug 2020
- AC1: 'Responses to Reviewer 3', Ying Li, 15 Oct 2020
RC2: 'Review of amt-2020-184', Anonymous Referee #1, 14 Aug 2020
- AC2: 'Responses to Reviewer 1', Ying Li, 15 Oct 2020

Peer-review completion

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

AR by Svenja Lange on behalf of the Authors (15 Oct 2020) Author's response

ED: Reconsider after major revisions (23 Oct 2020) by Roeland Van Malderen

ED: Referee Nomination & Report Request started (26 Nov 2020) by Roeland Van Malderen

RR by Anonymous Referee #3 (08 Dec 2020)

Suggestions for revision or reasons for rejection

Second review report on AMT-2020-184

I appreciate the authors providing detailed responses to my previous comments, which have helped me to understand the paper in more depth.
The proposed analytical technique has the potential to become a new definition of SSW. However, to confirm this method as a robust and standard definition of SSW, at least several major/minor SSW events must be additionally tested. Based on the responses to Points 2, 4, 16, and 20, this study is inconclusive, where further refinements are required, namely, by investigating a longer-data record. I am concerned, for example, with the response to Point 4, as the selection of TEA parameters, the corresponding height ranges, and their thresholds may be modified depending on each SSW event, and thus could produce ambiguity in defining major, minor, and final warmings.
I would like to suggest that the authors continue the analysis of several additional major/minor SSW events to make this method more concrete and to demonstrate fully the usefulness of the novel GNSS-RO data. However, if the authors are insistent about introducing this method to the SSW community in its present version, I look forward to a follow-up study in which the method is applied to a long-term dataset.

Specific comments to the responses
Point 1: In addition to the statements cited in the author’s response, Butler et al. (2015) also refers to some useful points about the SSW definition, including the technique’s statistical application to SSWs, consistency across observational and modeling studies, and detection of historical SSWs. These suggest that any new method should be tested with long-term records.
The following statement in the concluding section (Butler et al., 2015) provides a major summary of the new SSW definition.
“We believe a new definition should include, at a minimum, guidelines for determining a) the independence of closely timed events; b) the classification of split-type versus displacement-type events; and c) precise distinctions among major, minor, final, and Canadian SSWs.”
Have these requirements been met in the current study by considering only the single SSW event from 2009?

Point 3: I agree that the zonal wind in a narrow latitude band at a specific height may not be sufficient to define SSW. However, the effects of SSW have been commonly investigated in terms of the behavior of the polar vortex and its effects on stratosphere–troposphere coupling. Therefore, examination of the wind field, including the circulation reversal and the characteristics of planetary waves, is critical and should probably be included in a SSW definition.

Points 4 and 16: I understand that the thresholds of TEAs have yet to be confirmed, and they should be adjusted by repeating the analysis for a long-term dataset.
This study utilizes various parameters obtained from GNSS-RO measurements over a wide height range, which are summarized as a total of 12 values in Table 1. I am not fully convinced by the selection of only five of the 12 parameters. Are the other parameters useless?

Points 5 and 12: Unfortunately, I do not fully understand the response. Provided GNSS-RO data is assimilated into the ECMWF, they both naturally provide nearly the same results. Do the authors suggest employing ECMWF for application of this method to the larger re-analysis data from the past decades, which is much longer than the GNSS-RO records?

Point 6: I am interested in the retrieval technique when the model atmosphere is not used. Please show the citation for the non-optimized method.

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RR by Anonymous Referee #1 (14 Dec 2020)

RR by Anonymous Referee #2 (24 Dec 2020)

ED: Publish subject to minor revisions (review by editor) (13 Jan 2021) by Roeland Van Malderen

AR by Ying Li on behalf of the Authors (28 Jan 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (28 Jan 2021) by Roeland Van Malderen

Short summary

We introduce a new method to detect and monitor sudden stratospheric warming (SSW) events using Global Navigation Satellite System (GNSS) radio occultation (RO) data at high northern latitudes and demonstrate it for the well-known Jan.–Feb. 2009 event. We found that RO data are capable of SSW monitoring. Based on our method, a SSW event can be detected and tracked, and the duration and the strength of the event can be recorded. The results are consistent with other research on the 2009 event.