Estimating the maximum of the smoothed highest 3-hourly <i>a</i><i>a</i> index in 3&thinsp;d by the preceding minimum for the solar cycle

Du, Zhanle

doi:https://doi.org/10.5194/angeo-38-1237-2020

Articles | Volume 38, issue 6

https://doi.org/10.5194/angeo-38-1237-2020

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

https://doi.org/10.5194/angeo-38-1237-2020

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

Articles | Volume 38, issue 6

Regular paper

|

15 Dec 2020

Regular paper |

| 15 Dec 2020

Estimating the maximum of the smoothed highest 3-hourly aa index in 3 d by the preceding minimum for the solar cycle

Zhanle Du

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Final revised paper (published on 15 Dec 2020)
Preprint (discussion started on 03 Apr 2020)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Comment on Predicting the maximum aa/Ap index through its relationship with the preceding minimum', Anonymous Referee #1, 28 Apr 2020
- AC1: 'Geomagnetic index', Zhanle Du, 13 May 2020
- AC2: 'Geomagnetic activity index', Zhanle Du, 19 Jul 2020
- AC3: 'Geomagnetic activity index', Zhanle Du, 19 Jul 2020
RC2: 'Predicting the maximum aa/Ap index through its relationship with the preceding minimum', Anonymous Referee #2, 25 Jun 2020
- AC3: 'Geomagnetic activity index', Zhanle Du, 19 Jul 2020
- AC2: 'Geomagnetic activity index', Zhanle Du, 19 Jul 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (30 Jul 2020) by Elias Roussos

AR by Svenja Lange on behalf of the Authors (06 Aug 2020) Author's response

ED: Referee Nomination & Report Request started (26 Aug 2020) by Elias Roussos

RR by Anonymous Referee #2 (25 Sep 2020)

Suggestions for revision or reasons for rejection

The manuscript has clearly improved from earlier versions. It is now a lot clearer in its intent, and it provides a nice alternative to forecasting the strength of the next solar cycle by using Ap and aa indices. The results are certainly worth of being published; however, the manuscript still lacks clarity when transmitting the ideas. In particular, the reasoning behind using extreme smoothing and averaging is still not fully clear, and the excess of steps taken to arrive to the final quantities being investigated makes for a very large number of variables to follow through the text, many of which are not really discussed at length.
Some points I would like to be addressed by the author:

1. Title: I imagine there must be a middle ground between the original title and this very extensive title. I don't think it is necessary to fully describe the methodology in the title.

2. What do you mean mathematically by smoothing? It is a running average? A mean over X points? Also related:
Page 4, L1: You don't explain why is relevant to mimic a 13-month smoothing.
Page 4, L15: What is an accidental event and why do you need to smooth over such a large period?

3. I'm still very confused about the naming of variables. It seems that the author determined the maximum and minimum of aa every three days and smoothed the values over 121 points. Then they calculated the max/min of those values for every solar cycle and called that aa_Hmax, aa_Hmin and aa_Lmax, aa_Lmin, which are then the values used in the following sections to calculate correlations with sunspots. However, I can't find the place if the text where it is specified that aa_H,L_min,max are defined as the max over a solar cycle.

4. The manuscript is very repetitive. Ap and aa exhibit a very high correlation (as the author correctly describes), but then all the calculations are done independently for both Ap and aa, reaching extremely similar conclusions (which is expected) adding an extra and maybe unnecessary layer of complexity to the reading of the manuscript.

5. The writing and figures of the manuscript have significantly improved; however, I feel that the introduction is still confusing and need some extra attention. I'm suggesting some minor changes for the first section.
Abstract L1: "for an upcoming cycle" > "for an upcoming solar cycle"
Abstract L2: "service for planning future" > "service and for planning future"
Page 2, L21 (and other places through the manuscript): "geomagnetic activities" > "geomagnetic activity"
Page 2, L25: Solar cycle 24 already ended. Please update accordingly
Page 2, L26: "strengths" > "maximum strength" or maybe "maximum intensity"
Page 3, L3: "K indices" > "K index"?

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ED: Publish subject to minor revisions (review by editor) (09 Oct 2020) by Elias Roussos

AR by Svenja Lange on behalf of the Authors (22 Oct 2020) Author's response

ED: Publish as is (29 Oct 2020) by Elias Roussos

AR by Zhanle Du on behalf of the Authors (04 Nov 2020) Author's response Manuscript

Short summary

Predicting geomagnetic activity intensity for an upcoming solar cycle is important in space weather service and for planning future space missions. The maximum aa geomagnetic index for the solar cycle is found to be well correlated with the preceding minimum. The maximum aa index of solar cycle 25 is estimated to be about 29 % stronger than that of solar cycle 24. The maximum amplitude of the sunspot cycle is much better correlated with high geomagnetic activity than low geomagnetic activity.