Electromotive force in the solar wind

Narita, Yasuhito

doi:https://doi.org/10.5194/angeo-39-759-2021

Articles | Volume 39, issue 4

https://doi.org/10.5194/angeo-39-759-2021

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

https://doi.org/10.5194/angeo-39-759-2021

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

Articles | Volume 39, issue 4

Review paper

|

24 Aug 2021

Review paper |

| 24 Aug 2021

Electromotive force in the solar wind

Yasuhito Narita

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Final revised paper (published on 24 Aug 2021)
Preprint (discussion started on 12 Apr 2021)

Interactive discussion

Status: closed

RC1:
'Comment on angeo-2021-18', Anonymous Referee #1, 09 May 2021

The review article by Yasuhito Narita is on "Emf in solar wind" an important topic of relevance to both the Astrophysical dynamo and MHD turbulence community. It is well written and well-presented. The author has published other papers on this topic, one of which is cited but its results are not presented in detail. In my view, the paper will benefit from more depth and the breadth, being a review article. It would be relevant to get a glimpse of the entire body of work done in the area and allied areas (unless there is a page limit). For e.g. the classical works or review articles by Paul Roberts on dynamo theory, Keith Moffatt on helicity, for example, are not cited. There are hardly 10 referenes !

A specific comment on one of the conclusions - why is it so that the emf can be reconstructed better by considering the beta and gamma terms. Which of these two is contributing more? The author being an expert in this area could shed some light on this interesting conclusion. If this is difficult to understand, then the author should say so along with the reasons.

Citation: https://doi.org/10.5194/angeo-2021-18-RC1
- AC1: 'Reply to RC1 and RC2', Yasuhito Narita, 08 Jun 2021
  
  Thank you very much for carefully reading the manuscript and raising comments and suggestions. Criticism and suggeestions are well taken. My reply comments and the revised manuscript are uploaded in a separated (merged) PDF file.
  
  Citation: https://doi.org/10.5194/angeo-2021-18-AC1
RC2:
'Comment on angeo-2021-18', Anonymous Referee #2, 14 May 2021

This paper is well written and covers an important topic. This (mini) review gives a clear indication that the study of the EMF in the solar wind is a valuable activity (and I agree with the author on this). The mean induction equation, with the alpha, beta and gamma split, is presented in equation (5). Shortly after, different expressions are given for alpha and beta, and then gamma. Although there are similarities between the expressions, the assumptions going into deriving those terms are very different (compare Krause and Radler with Yokoi). Some more information on the applicability of these models for the solar wind would be helpful. The author then highlights solar wind studies which use various forms of the EMF expression and discusses how effective they have been. What he has written is very clear.

I think there could be some more discussion on the physical importance of the alpha, beta and gamma effects for the solar wind. I don't think the appendix is necessary and could be replaced, without much loss. For example, the author includes magnetic helicity in the appendix, but this does not really feature in the main text.

Citation: https://doi.org/10.5194/angeo-2021-18-RC2
- AC2: 'Reply', Yasuhito Narita, 08 Jun 2021
  
  For a technical reasion it is not possible to post my comments as a separate line. Please see my reply comments in the attached material to "Reply to RC1 and RC2".
  
  Citation: https://doi.org/10.5194/angeo-2021-18-AC2

Peer review completion

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

ED: Publish subject to revisions (further review by editor and referees) (09 Jun 2021) by Anna Milillo

AR by Yasuhito Narita on behalf of the Authors (09 Jun 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (10 Jun 2021) by Anna Milillo

RR by Anonymous Referee #2 (26 Jun 2021)

RR by Anonymous Referee #1 (12 Jul 2021)

Suggestions for revision or reasons for rejection

The author has changed the article from a mini-review to a regular article. More data, results and a table have been added which has enhanced the quality of the paper on an important topic. I have only three comments which in my view should be addressed before the paper is accepted, and few minor editorial corrections. These can be easily incorporated in the manuscript if the author thinks them to be relevant.

Comments
1) Since this is now a regular article, the article needs some more modification to reflect this. For e.g. the abstract needs to change to reflect some of the (new) observations mentioned in "summary and outlook". As done in his previous article in Ann Geo, Narita & Voros (2018) the author could include some more details on the methods, for the completeness of this article and for the benefit of the readers.

2) On page 9, the author says "note that the alpha effect test fails on one hand, and the mean-field model can qualitatively reproduce the observed electromotive force." This is an intriguing result. The scaling analysis that follows (eq. 22) says that the alpha term should be almost as important as the beta term (in fact, 4 times larger) which is as important as the gamma term. Isn't this contradictory to the fact that the alpha effect test (section 3.3.1, fig 3) fails, according to the author himself? The author could shed more light on this aspect if he agrees with the contradiction. Perhaps the method used for alpha-test needs a correction/modification or a caveat?

3) Since this a regular article, the author should more clearly demarcate what is new here with respect to Narita & Voros (2018). Adding some text in the introduction and summary/outlook sections would address this. One page 1, the author says "This article presents the emf studies in the solar wind in view of the current in situ observations in the inner heliosphere such as Parker Solar Probe (since 2018), Solar Orbiter (since 2020), and BepiColombo’s cruising to the Mercury orbit (since 2018)". However, the data considered is not from any of these new missions, but from Helios, same as in Narita & Voros (2018).

Minor points
1) Equation (5) occurs twice.
2) Typo/spelling errors in lines 16, 57, 101, 105, 168
3) Full stop missing at line 116 and few other places
4) Line 181 - "both the" instead of "the both"
5) Lines 48-49, 62, 81 - "the second term the ...", "the third term the ..." , etc needs to be changed to "the second term represents/is the ..." and so on.

Please check the draft for some additional typos that I may have missed. Nowadays there are many auto spell-check softwares available.

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ED: Publish subject to minor revisions (review by editor) (14 Jul 2021) by Anna Milillo

AR by Yasuhito Narita on behalf of the Authors (22 Jul 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (23 Jul 2021) by Anna Milillo

Short summary

The concept of electromotive force appears in various electromagnetic applications in geophysical and astrophysical fluid studies. The electromotive force is being recognized as a useful tool to construct a more complete picture of turbulent space plasma and has the potential to test for the fundamental processes of dynamo mechanism in space.