Multiscale estimation of the field-aligned current density

Bunescu, Costel; Vogt, Joachim; Marghitu, Octav; Blagau, Adrian

doi:https://doi.org/10.5194/angeo-37-347-2019

Articles | Volume 37, issue 3

https://doi.org/10.5194/angeo-37-347-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Special issue:

Dynamics and interaction of processes in the Earth and its...

https://doi.org/10.5194/angeo-37-347-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 37, issue 3

Regular paper

|

24 May 2019

Regular paper |

| 24 May 2019

Multiscale estimation of the field-aligned current density

Costel Bunescu, Joachim Vogt, Octav Marghitu, and Adrian Blagau

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Final revised paper (published on 24 May 2019)
Preprint (discussion started on 06 Jul 2018)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Reviewer's comments on ANGEO-2018-70', Anonymous Referee #1, 13 Aug 2018
- AC1: 'Response to Report 1', Costel Bunescu, 30 Nov 2018
- AC2: 'Response to Report 2', Costel Bunescu, 30 Nov 2018
- AC3: 'Revised manuscript -changes indicated', Costel Bunescu, 30 Nov 2018
- AC5: 'Revised manuscript', Costel Bunescu, 30 Nov 2018
RC2: 'Referee Comment to Bunescu et al. (2018)', Anonymous Referee #2, 14 Aug 2018
- AC2: 'Response to Report 2', Costel Bunescu, 30 Nov 2018
- AC1: 'Response to Report 1', Costel Bunescu, 30 Nov 2018
- AC4: 'Revised manuscript -changes indicated', Costel Bunescu, 30 Nov 2018
- AC6: 'Revised manuscript', Costel Bunescu, 30 Nov 2018

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (04 Dec 2018) by Rumi Nakamura

AR by Costel Bunescu on behalf of the Authors (05 Dec 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (06 Dec 2018) by Rumi Nakamura

RR by Anonymous Referee #2 (11 Jan 2019)

RR by Anonymous Referee #1 (15 Jan 2019)

Suggestions for revision or reasons for rejection

Reviewer’s comments on ANGEO-2018-70 (revised) by Bunescu et al.

This manuscript applies the minimum variance analysis (MVA) to in-situ magnetic field data during auroral crossings. MVA is applied to a set of sliding windows of across the data with differing window lengths to attempt to examine the orientation, planarity and field-aligned currents at different scales. As noted previously, being able to determine current sheet orientation to correct for this in field-aligned current calculation is useful, however the non-orthogonality of the data remains a major unaddressed issue.

Technical Comments

The authors have removed the weighting factors that were present in the previous version of this manuscript. However, since they are not using orthogonal basis functions for this analysis means that the interpretation of their analysis remains challenging.

The manuscript describes the MSMVA procedure as having an embedded scale filtering by removing an average over the window to which the analysis is applied (Page 7, lines 18-23). This procedure is somewhat unclear, however based on later descriptions that indicate that B is determined from a linear fit across the window (Page 8, lines 4-10), it appears that the average magnetic field within the window is then removed from the same window. This should have no effect on the signal. The effect of large-scale FACs on smaller-scale FACs can only be removed if the sliding average window is larger than the scale over which the currents are calculated.

The manuscript describes that this technique provides estimates of the ‘local FAC density present at various scales’ but that the current cannot be integrated across scales. I would suggest instead that this technique provides an average FAC across scales and some indication of the dominant scale given by peaks in . In fact, this appears to be how this technique is interpreted in the manuscript. The fact that larger scales tend to be focussed on may be as a result of not apply the scale correction to all the spectrograms (page 8, line 20).

While I understand that the application of MVA across a range of scales can potentially provide more information on the orientation of various magnetic field perturbations observed by spacecraft as they pass over the aurora, I struggle to understand the benefit of the analysis as presented. How is one expected to interpret the results if the FACs at different scales are not isolated from one another? For example, comparing the time-series of FACs at two different scales would not appear to be meaningful. How does this analysis differ from computing MVA between local maxima and minima in the magnetic field data?

Specific Comments

Within Section 4, there are a number of comparisons between single- and dual-spacecraft currents and those calculated from the MSMVA technique. It may help the reader if this information was tabulated to aid comparisons.

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ED: Publish subject to revisions (further review by editor and referees) (15 Jan 2019) by Rumi Nakamura

AR by Costel Bunescu on behalf of the Authors (25 Feb 2019)

ED: Referee Nomination & Report Request started (26 Feb 2019) by Rumi Nakamura

RR by Anonymous Referee #1 (03 Apr 2019)

ED: Publish subject to minor revisions (review by editor) (03 Apr 2019) by Rumi Nakamura

AR by Costel Bunescu on behalf of the Authors (23 Apr 2019) Author's response Manuscript

ED: Publish subject to technical corrections (29 Apr 2019) by Rumi Nakamura

AR by Costel Bunescu on behalf of the Authors (08 May 2019) Author's response Manuscript