The increase in the curvature radius of geomagnetic field lines preceding a classical dipolarization

Saka, Osuke

doi:https://doi.org/10.5194/angeo-38-467-2020

Articles | Volume 38, issue 2

https://doi.org/10.5194/angeo-38-467-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/angeo-38-467-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 38, issue 2

Regular paper

|

07 Apr 2020

Regular paper |

| 07 Apr 2020

The increase in the curvature radius of geomagnetic field lines preceding a classical dipolarization

Osuke Saka

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Final revised paper (published on 07 Apr 2020)
Preprint (discussion started on 29 Aug 2019)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'auroral physoics, magnetospheric physics', Anonymous Referee #1, 20 Sep 2019
- AC2: 'Reply to comments of referee #1', Osuke Saka, 25 Oct 2019
RC2: 'Review of Saka 2019 manuscript', Anonymous Referee #2, 20 Sep 2019
- AC3: 'Reply to comments of referee #2', Osuke Saka, 25 Oct 2019
AC1: 'Replies to referee #1 and referee #2', Osuke Saka, 26 Sep 2019

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (18 Nov 2019) by Elias Roussos

Dear Dr. Saka,

thank you for submitting your manuscript "The increase of curvature radius of geomagnetic field lines preceding a classical dipolarization" to Annales Geophysicae. I have now gone through the interactive discussion, including the reviews by two referees and your replies to them.

As you realise, the reviewers' opinions are strongly diverging, with one recommending immediate publication, the other one rejection. Such a strong divergence is a rare and uncomfortable situation, which forces me to also review the manuscript myself, causing extra (but unavoidable) delays in the review process.

Through this extensive evaluation my remarks are:

a) Both reviewers agree that your manuscript contains interesting ideas that merit further research
b) While reviewer #1 is very positive, his/her review does not contradict any of the specific issues raised by reviewer #2. For the issues raised by reviewer#2 I therefore only relied on your answers in the interactive discussion and my own reading of your work and/or discussion points. Nevertheless, the very positive remarks by reviewer #1 are not ignored.
c) I certainly agree with many of the issues raised by the reviewer #2, even though my expertise does not allow me to peer into the small details of your study. You provide specific answers with references, although I notice in many cases that you provide references that point to single case studies in order to back-up your points, against the remarks from reviewer #2 who identifies deviations from statistically significant observations (e.g. about the distance that dipolarizations are triggered).

Given the above, my decision is to offer you the possibility to revise your manuscript. I can only assign this revision as major and cannot guarantee publication at this point. I may have to consult a 3rd reviewer in order to reach a final decision.

I recommend that you revise your manuscript along the lines of your answers given in the interactive discussion. I also encourage you to elaborate on the significance of some of the observations you cite and discuss why single events are sufficient to change the big picture. E.g. you remark that Saka and Hayashi (2017) describe a case of geosynchronous initiation of a dipolarization, but is that case a rare event or one that should change the big/prevailing picture about "classical dipolarization" at ~10 R_E?

Along with the revision, please provide a formal reply to all the reviewer comments (even if you use the same ones as in the interactive discussion), indicating where in the revision changes to the original manuscript can be identified.

Kind regards,

Elias Roussos

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AR by Osuke Saka on behalf of the Authors (28 Nov 2019) Author's response

ED: Referee Nomination & Report Request started (16 Dec 2019) by Elias Roussos

RR by Anonymous Referee #2 (05 Jan 2020)

RR by Anonymous Referee #3 (17 Jan 2020)

Suggestions for revision or reasons for rejection

Review of The increase of curvature radius of geomagnetic field lines preceding a classical dipolarization by Osuke Saka.

The paper proposes an idea on the sequence of events that might have led to inner magnetosphere dipolarization during a substorm event, which was analyzed in earlier papers by the same author. The topic of the paper is well within the scope of the AG journal. The discussed idea is nonconventional and contains certain novelty. It is the lack of details in the proposed scenario and absence of observational evidence that make me unable to conclude on validity of this reasoning. In my opinion, the paper may be considered for publication only after addressing the following major issues:

1. The paper is too much detached from the discussed observations. Numerous parts of the paper refer to spacecraft data and figures that were presented in earlier publications of the author. I believe that a research paper should not depend heavily on another paper. On the contrary, most of the data that is discussed in the present paper, should also be readily available for readers in the paper’s figures. Of course, the figures may not be just copied from a previous research. Instead, they should be prepared for the purposes of the present paper.

2. The author supports the presented idea by some criteria estimates rather than by real observations. For example, the author derives the threshold for the ballooning instability and claims that the condition is fulfilled. On the other hand, there is no observational figure showing signatures of the ongoing instability development.

Not being aware of whether the ballooning instability was excited, the author further suggests that the instability drives a slow wave (the next event in the author’s scenario). Here again, there are neither provided observational evidences of the presence of the slow wave, nor theoretical details are explained how the ballooning instability generates such a slow mode wave. If such details can be found in another paper, then a short summary on the process would be reasonable to include in the present paper. By the way, it may be better to give a reference to Kadomtsev in English rather than in Japanese or Russian.

A similar situation concerns the next steps in the author’s scenario – azimuthal spreading of plasmas, decrease of the radial pressure gradient, reduction of the cross-tail currents and pileup of the magnetic field.

Thus, the paper could be more supported by specific observations (perhaps by a new event with many spacecraft). An alternative way to improve the paper would be developing a more complete and consistent theoretical model. Unfortunately, at this stage the paper looks like a presentation of a concept rather than a rigorous theoretical or observational analysis.

3. Another major concern is that the paper does not provide adequate literature research on the paper’s main topic (inner magnetosphere and magnetotail dipolarization and dipolarization fronts).

For example, from VAP and earlier observations it is known that dipolarization fronts may reach geostationary and deeper altitudes (down to L=4):

Moore, T. E., et al., (1981). Propagating substorm injection fronts. Journal of Geophysical Research, 86, 6713–6726. https://doi.org/10.1029/JA086iA08p06713

Reeves, G. D., et al., . (1990).Multi-satellite measurements of the substorm injection region. Geophysical Research Letters, 17, 2015–2018. https://doi.org/10.1029/GL017i011p02015

Ohtani, S., et al., (2018). Spatial development of the dipolarization region in the inner magnetosphere. Journal of Geophysical Research: Space Physics, 123, 5452–5463. https://doi.org/0.1029/2018JA025443).

Conditions that define the penetration depth were experimentally discussed, e.g., in

Dubyagin, S., et al., (2011). Can flow bursts penetrate into the inner magnetosphere? Geophysical Research Letters, 38, L08102. https://doi.org/10.1029/2011GL047016

An global modeling analysis of dipolarization was made recently in

Merkin, V. G., et al., (2019). Contribution of bursty bulk flows to the global dipolarization of the magnetotail during an isolated substorm. Journal of Geophysical Research: Space Physics, 124. https://doi.org/10.1029/2019JA026872

The authors may want to go through reference lists in the above papers in order to construct a more appropriate literature analysis in the present paper.

4. The author relies on Pi2 pulsations onset time at various ground stations. If I understand correctly, the onset of Pi2 pulsations is needed for timing of the dipolarization. It is not explained though how the Pi2 pulsations fit in the author’s model. As it follows from some models, Pi2 pulsations can occur independently from dipolarization (https://doi.org/10.1002/2014JA020625) Also, it has been suggested that low latitude Pi2 pulsations are directly driven by compressional pulses https://doi.org/10.1029/2000JA000158 . High-latitude Pi2 pulsations were suggested to be driven by magnetospheric buoyancy waves https://doi.org/10.1002/2013JA019633.

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ED: Reconsider after major revisions (further review by editor and referees) (22 Jan 2020) by Elias Roussos

AR by Osuke Saka on behalf of the Authors (14 Feb 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Feb 2020) by Elias Roussos

RR by Anonymous Referee #3 (29 Feb 2020)

Suggestions for revision or reasons for rejection

2nd review of The increase of curvature radius of geomagnetic field lines preceding a classical dipolarization by Osuke Saka

I have read the revised version of the paper two times. I am not sure that I do follow all the logical steps and arguments of this paper since I still find the paper to be more a conceptual model rather than a proven algorithm for a process that might lead/initiate the magnetotail dipolarization. Nonetheless, I admit that the author wrote the paper fair enough for a reasonable contribution in the scientific discussion in the community about the processes that precede the magnetotail dipolarization. Therefore, I can imagine this paper be published in AG when several minor elements of the paper are improved (below).

Minor comments:

1.

>Kadomtsev [1976] was published only in Russian and Japanese.

The Pergamon Press published the English translation of the Kadomtsev’s book in 1982 (ISBN-10: 0080250181, ISBN-13: 978-0080250182)

2.

>An arrival of low entropy plasma bubbles into the inner magnetosphere [e,g., Dubyagin et al., >2011] may breakdown the last open trajectories of plasma sheet electrons. This may cause N-S >auroras from poleward aurora boundary [Saka et al., JASTP, 145, 114-124, 2016], However, if >enough field line stretching was developed in the midnight magnetosphere prior to the arrival of >the bubble, the plasma bubble may trigger auroras arising out of arc (substorm onset). The latter >case may not be inconsistent with the global dipolarization model of inner magnetosphere >[Merkin et al., 2019] where intensity and occurrence of dipolarization front (DF) may increase >abruptly at substorm onset. These topics will be the subject of future study.

I don’t think the author can ignore the work of Dubyagin et al., 2011 (https://doi.org/10.1029/2011GL047016) in this paper, because the author directly touches the question of the penetration depth of BBFs, e.g., Lines 234-235: “Consequently, this scenario requires that the BBFs are not necessary to reach inner magnetosphere to trigger the substorm onset at lower latitudes. “. I also strongly suggest to add here another a reference to Shiokawa et al., 1997 (https://doi.org/10.1029/97GL01062).

In turn, the work of Merkin et al., 2019 (https://doi.org/10.1029/2019JA026872) is completely in accord with the discussed in the paper in Line 400 seminal work by Baumjohann et al., 1999 on the tailward expansion of the global dipolarization. Taking into account that Merkin’s work is a significant contribution to the question the author is addressing in the paper, I believe that the author cannot ignore such results in the present paper.

3.
The paper also lacks discussion of current system that couples deeply injected plasma sheet bubbles with the ionosphere. A great contribution on this topic was made by Yang et al., 2012 https://doi.org/10.1029/2011JA017415 and is ought to be mentioned and discussed in the paper (as least in the discussion section around Line 415).

Line 152: Should tapped be trapped?

Line 423: The statement „No data sets were used in this article.“ is not consistent with the contents of Figures 1, 4 and 7.

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ED: Publish subject to minor revisions (review by editor) (29 Feb 2020) by Elias Roussos

AR by Osuke Saka on behalf of the Authors (03 Mar 2020) Author's response Manuscript

ED: Publish as is (05 Mar 2020) by Elias Roussos

AR by Osuke Saka on behalf of the Authors (10 Mar 2020)

Short summary

The first 10 min interval of Pi2 onset is the most active period of substorms composed of field line deformations associated with an increase in curvature radius of flux tubes and their longitudinal expansion. The flux tube deformations were triggered by the ballooning instability of slow magnetoacoustic waves upon arrival of the dipolarization front from the tail. They preceded the classical dipolarization caused by the reduction of cross-tail currents and resulting pileup of the field lines.