Estimating the fate of oxygen ion outflow from the high-altitude cusp

Krcelic, Patrik; Haaland, Stein; Maes, Lukas; Slapak, Rikard; Schillings, Audrey

doi:https://doi.org/10.5194/angeo-38-491-2020

Articles | Volume 38, issue 2

https://doi.org/10.5194/angeo-38-491-2020

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

https://doi.org/10.5194/angeo-38-491-2020

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

Articles | Volume 38, issue 2

Regular paper

|

08 Apr 2020

Regular paper |

| 08 Apr 2020

Estimating the fate of oxygen ion outflow from the high-altitude cusp

Patrik Krcelic, Stein Haaland, Lukas Maes, Rikard Slapak, and Audrey Schillings

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Final revised paper (published on 08 Apr 2020)
Preprint (discussion started on 30 Aug 2019)

Interactive discussion

Status: closed

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

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- Supplement

SC1: 'Reviewing "Estimating the fate of oxygen ion outflow from the high altitude cusp"', Matthias Förster, 03 Sep 2019
RC1: 'Reviewer comment on paper angeo-2019-125', Anonymous Referee #1, 18 Sep 2019
- AC1: 'Authors response to reffery', Patrik Krcelic, 08 Nov 2019
RC2: 'Review 'Estimating the fate of oxygen ion outflow from the high altitude cusp'', Anonymous Referee #2, 02 Oct 2019
- AC2: 'Authors response to the reffery', Patrik Krcelic, 08 Nov 2019

Peer-review completion

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

ED: Publish subject to revisions (further review by editor and referees) (13 Nov 2019) by Minna Palmroth

AR by Patrik Krcelic on behalf of the Authors (15 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (20 Nov 2019) by Minna Palmroth

RR by Anonymous Referee #1 (12 Dec 2019)

Suggestions for revision or reasons for rejection

I am overall satisfied with the responses provided by the Authors as well as the corrections which have been implemented to the manuscript. Below are a few additional comments and suggestions after reading the revised version. My recommendation is to accept this manuscript for publication provided those mostly minor comments have been addressed adequately.

- p.2 l.21: "> 6 RE <"; I guess the second "<" is a typo.
- p.3 l.25: Please define EFW.
- p.6 l.25: Could you please specify which time resolution was used for the OMNI data? Given that you use Dst (as opposed to SYM-H), I presume it is the hourly data; is that so?
- p.13, l.10: Does the 120 min result come from the analysis using the average parallel velocity <v_par>? Or does it combine results from the three analyses (<v_par>, <v_par>-sigma_par, <v_par>+sigma_par)? I suggest to specify it in the text.
- p. 13 l. 15: There is a typo in the power of 10 (in the ion outflow value).
- Fig. 8 caption: I think you have forgotten to remove the mention to upper/lower quartiles; please update the caption accordingly.
- Fig. 9: Sorry for only noticing it now, but the <v_par>+sigma_par panel seems to have the data shifted one bin "downwards" compared to other two panels. Is this a bug in the code for plotting the figure? Please check, and fix if necessary.
- Fig. 9 caption: Same as for Fig. 8, the mention to upper/lower quartiles needs to be removed.
- p.13 l.24: I suggest to refer to the new figures in the annex (A1, A2, B1).
- p.15 l.3: How did you estimate that the changes would be "a couple percent" in the absence of data gaps?
- Fig. 10: I suggest to add the unit (nT) to the Dst values in the top-right-hand corner of each panel.
- Fig. 10 caption: Instead of "labels", shouldn't it be "colors" (which are the same as in Fig. 8)? To me, "labels" would rather refer to the top-right-hand-corner texts about Dst values, which are therefore different from those in Fig. 8. Please also add the unit for Dst values (nT) in the top-right-hand corner of each panel.
- Fig. 11: Similarly to Fig. 9, the third panel (Dst < -20 nT) seems to have all its data shifted downwards by one bin; please check and correct if needed.
- Fig. 11 (also): I am again a bit intrigued by the isolated black pixels. In particular, I notice that in the middle panel (0 > Dst > -20 nT) the isolated black pixel near X = 1 Re, Y = 8 Re is at the same location as the one I was asking about during the first round of comments (in the previous version of Fig. 9, third panel). Since in that first case you found that it was related to a bug in the plotting code, I would recommend that you double check whether the same bug is present in the plotting script of Fig. 11.
Regarding the isolated black pixels in the first panel of Fig. 11 (Dst > 0 nT), I suspect that they might be related to the very low number of samples, especially in EDI data (see Fig. A1). In fact, I am a bit worried that quiet conditions have many bins with extremely few (based on Fig. A1, it seems that it could be even less than 10) minutes of observations of convection velocities. How reliable is the analysis when so few observations are available? In that sense, I have the feeling that the discussion on p. 15 l.1-3 needs to be expanded, as presently it only addresses the effect of data gaps but does not mention the cases where the statistics has been obtained with very few measurements. One suggestion I may give is to select a reasonable threshold value (would 30 or 50 min be suitable?) below which the data could still be plotted (provided there are at least 3 minutes of observations, as stated on p.5 l.1) but highlighted as less certain in Fig. 11 – for instance, by adding some transparency to the affected pixels. This would not change the conclusions, but could provide some measure of the uncertainty, which I believe would be useful when interpreting the results.
- Fig. 11 caption: Same as for Fig. 10 caption regarding the word "labels", that I would suggest replacing with "colors".
- p.17 l.15: I am not sure that I understand what is implied by "We did not take those into account" (regarding sudden storm commencement conditions). Do you mean that you removed them from the Dst>0 dataset, or on the contrary that you did not differentiate them from quiet conditions? Please clarify this statement.
- Appendix figures: Is there a reason why they are called A1, A2 and B1, rather than A1, A2 and A3?

Finally, I would recommend carrying out an overall language check, which could improve the quality of the manuscript (usage of article "the", hyphenation, third person singular-vs-plural present tense, tense consistency in sentences, typos...). Please double check also the \citep vs \citet usage (e.g., p.18 l.16, p.18 l.23).

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RR by Anonymous Referee #2 (22 Dec 2019)

Suggestions for revision or reasons for rejection

Thanks for the revised version of the manuscript. I apologize for the delay in the response. Most of my comments have been appropriately addressed. However, in my opinion, these 2 main comments still deserve some clarification / justification in the main manuscript.

MAIN Comments

> There is a large difference between the EDI and CODIF perpendicular velocity data. The CODIF perpendicular velocities have similar values to CODIF parallel velocities. This velocities go up to 120 km/s, and are def- initely not from the convection. EDI data give values of around 15 km/s which is what we expect convection to be. At this point we do not know how to explain the CODIF perpendicular velocity measured in the cusps.

You do not comment on that in the new version. I think it should be mentioned at the very least. Why trusting CODIF Vpar if Vperp is believed to be wrong? Vpar from CODIF is one of the major measurements this work employs. This has to be addressed somehow. I am not familiar with the CODIF dataset, is it a well-known problem? Can you provide references that support this way of using the data?

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> Another main concern to me is if the dataset you use corresponds truly to cusps observations. For EDI you use TS96 to decide if you are in the cusps or not only, right? You should check other parameters as well when available, as for instance plasma beta.For CODIF dataset you do a much more accurate filtering of your dataset.

> The plasma beta number is not always available when we have EDI data. We have decided to analyse each dataset separately and than combine the average values to get our estimate.

You need to comment on the possible implications (or alternatively justify) the different treatment of the 2 datasets. You combine measurements of different nature, filtered using different criteria. I am worried, as mentioned before, whether your EDI measurements truly correspond to cusps measurements most of the time or not. Could you please develop on that?

MINOR comments

P1 L16 an important

P2 L21 extra '>' ?

P8 L7 'on the TS96...'

P13 L15 '0' should be part of the exponent. What is the effective cross-section of the tail you consider? What is the total average O+ flux (ions/s)?

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ED: Publish subject to revisions (further review by editor and referees) (28 Dec 2019) by Minna Palmroth

AR by Natascha Töpfer on behalf of the Authors (10 Feb 2020) Author's response

ED: Referee Nomination & Report Request started (10 Feb 2020) by Minna Palmroth

RR by Maxime Grandin (14 Feb 2020)

RR by Anonymous Referee #2 (08 Mar 2020)

ED: Publish subject to technical corrections (10 Mar 2020) by Minna Palmroth

Short summary

In this paper we have used Cluster EDI data in combination with the CODIF cusp dataset from Slapak et al. (2017) to obtain parallel and convection velocities for oxygen ions; 69 % of total oxygen outﬂow from the high-altitude cusps escapes the magnetosphere on average; 50 % escapes tailward beyond the distant X-line. The oxygen capture-versus-escape ratio is highly dependent on geomagnetic conditions. During active conditions, the majority of oxygen outﬂow is convected to the plasma sheet.