the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jul 2022
Statistical distribution of mirror mode-like structures in the magnetosheaths of unmagnetised planets: 1. Mars as observed by the MAVEN spacecraft
Cyril Simon Wedlund
Martin Volwerk
Christian Mazelle
Sebastián Rojas Mata
Gabriella Stenberg Wieser
Yoshifumi Futaana
Jasper Halekas
Diana Rojas-Castillo
César Bertucci
Jared Espley
Abstract. In this series of papers, we present statistical maps of mirror mode-like (MM) structures in the magnetosheaths of Mars and Venus and calculate the probability of detecting them in spacecraft data. We aim to study and compare them with the same tools and a similar payload at both planets. We consider their dependence on Extreme Ultraviolet (EUV) solar flux levels (high and low), and, specific to Mars, on Mars Year (MY) as well as atmospheric seasons (four solar longitudes Ls). We first use magnetic field-only criteria to detect these structures and present ways to mitigate ambiguities in the nature of the detected structures. In line with many previous studies at Earth, this technique has the advantage of using one instrument (a magnetometer) with good time resolution facilitating comparisons between planetary and cometary environments. Applied to the magnetometer data of the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft from November 2014 to February 2020 (MY32–MY35), we detect structures closely resembling MMs lasting in total more than 170,000 s, corresponding to about 0.1 % of MAVEN's total time spent in the Martian plasma environment. We calculate MM-like occurrences normalised to the spacecraft's residence time during the course of the mission. Detection probabilities are about 1 % at most for any given controlling parameter. In general, MM-like structures appear in two main regions, one behind the shock, the other close to the induced magnetospheric boundary, as expected from theory. Detection probabilities are higher on average in low solar EUV conditions, whereas high solar EUV conditions see an increase in detections within the magnetospheric tail. We tentatively link the former tendency to two combining effects: the favouring of ion cyclotron waves the closer to perihelion due to plasma beta effects, and, possibly, the nongyrotropy of pickup ion distributions. This study is the first of two on the magnetosheaths of Mars and Venus.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(4126 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Cyril Simon Wedlund et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-634', Anonymous Referee #1, 30 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-634/egusphere-2022-634-RC1-supplement.pdf
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AC1: 'Reply on RC1', Cyril Simon Wedlund, 05 Feb 2023
Dear reviewer,
We would like to thank the two anonymous referees for their constructive comments, questions and suggestions. Please find our answers below, with all the points raised during the review addressed in the PDF attached.Throughout, our responses are marked as “AC1” and shown in italic, whereas all other instances (non-italic text) are the original reviewer comments and questions.
Best regards,
CSW et al. 05 February 2023-
AC3: 'Reply on AC1', Cyril Simon Wedlund, 05 Feb 2023
We discovered a typo in our response to Reviewer 1, on page 6, "Line 422" of the PDF. "10/7" should read instead of "10/3", obviously (70% of the orbit is taken into account, hence a factor 1.5 of multiplication). The text should be:
"AC1: This is a very good point which we had originally missed, and we are grateful to the reviewer for it. The histogram of Fig. 6 assumes a full day of observation, but because we have removed the events in the solar wind and MAVEN spends about 30% of its time on average in the solar wind (see, for example, the Figure 1 of Simon Wedlund et al. 2022c), all numbers should be compensated for this lack of temporal coverage by at least an equal number (multiplied by a factor 10/7 ~ 1.5 at least). To clarify this, we first add some statistics in Table 3 (see below). [...]"
Citation: https://doi.org/10.5194/egusphere-2022-634-AC3
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AC3: 'Reply on AC1', Cyril Simon Wedlund, 05 Feb 2023
-
AC1: 'Reply on RC1', Cyril Simon Wedlund, 05 Feb 2023
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RC2: 'Comment on egusphere-2022-634', Anonymous Referee #2, 28 Dec 2022
Mirror Modes (MMs) are often observed in the magnetosheath of many solar system objects, like Earth, Venus, Mars and comets. This paper presents the statistical maps of mirror mode-like (MM) structures in the magnetosheath of Mars based on the magnetometer data only of MAVEN from November 2014 to February 2021 (MY32-MY35). Based on the magnetic field-only criteria and two mitigation strategies, 176,041 MM-like structures are detected in their final database. Then, they analyze the characteristics and calculate the detection probabilities of MM-like structures with respect to several controlling parameters (including Mars Years, EUV flux and Mars season, Ls) and map them in the magnetosheath of Mars. The results indicate MM-like structures appear in two main regions: behind the shock and close to the induced magnetospheric boundary. And the detection probabilities are higher with low solar EUV flux, which contradicts the prospect, explained by two combining effects: plasma beta effects and non-gyrotropy of pickup ion distributions. The detection method and mitigation strategies are well described and the properties of MMs are well shown by plenty of figures. Before I recommend accepting to publication in AG, below comments/suggests needs to address.
As shown in the introduction, MMs likely share a common ancestor with magnetic holes (MHs); statistical characteristics of magnetic holes have already been analyzed in the Martain magnetosheath. For instance, Huang et al. (2021, ApJ, 922:107) analyzed the distribution and parameter characteristics of kinetic-size magnetic holes (KSMHs) in the Martain magnetosheath using MAVEN’s data and tries to explain the mechanism of KSMHs as electron vortex. These results may also shed light on the mechanism of MMs. The authors should try to compare the properties between MMs and MHs to figure out the relationship between these structures and their mechanisms and their differences.
Line 185-186: “moreover this ensures that rotations could be calculated for trains of MM-like structures for which the 2-min windowed background magnetic field values would be representative.” This sentence is complicated and vague.
Line 245-250: “Conversely, we also expect the method to keep structures that are likely not MMs but situated in the magnetosheath (with B and N in phase).” What do the authors want to express by this sentence? Besides, the authors try to keep the isolated structures out of the final database to make the results accurate. Now that, what does this sentence “As a consequence, on this criterion only (isolated structure), the frequency of MM-like detections in our final database could be underestimated by at least 10%.” mean? Should the isolated structures be included in the database or not?
Line 277-278: “…, which we expect to be about 25%, as evaluated from visual comparisons in a subset of events (see Figs. 1 and 2).” How do the authors evaluate the extent of the underestimation and from which subsets of events?
Line 392-396: “Secondly, the two detection methods differ significantly: our B-field-only criteria detection permits us to capture trains of short events with 1-s resolution at the expense of an ambiguity in the nature of the detected structure, whereas Ruhunusiri et al. (2015) used wave analysis techniques based on transport ratios with a cruder time resolution (4–8 s with a Fourier transform on consecutive 128 s intervals).” The authors try to compare the detection probabilities between this work and Ruhunusiri et al. (2015) and explain the lower estimate due to the detection method. However, the lower resolution in Ruhunusiri et al. (2015) could also lead to the omission of smaller structures, resulting in a lower estimate for their results. It’s hard to make a comparison and draw a conclusion in this way.
Line 427-428: “…, we cannot compare absolute detection numbers with the other MYs without first normalising to the spacecraft’s residence time during that period.” The authors could try to calculate the detection probabilities of each Mars year, so far as the absolute detection numbers and the spacecraft’s residence time can be obtained, as shown in Fig. 8.
Table3: "NMM represents the total number of MM-like events found (equivalent to a duration in s because of the magnetometer resolution of 1 s)”.
Line 419-421: “On average throughout MY32 to MY35 with MAVEN, we find â¨Nâ© = 68±43 structures per day (ignoring single isolated 1-s events, see Sect. 2.2.2) fulfilling the criteria of Table 1.”
Line 429-430: “Finally, if we assume that most structures last 5–10s on average, we end up with 68/10–68/5 ≈ 7–14 MMs/day in Mars’ magnetosheath.”
What’s the definition of an MM-like event, a structure and a MM? Are they the same or not? What is the relationship between them?
Line 445: “… , with the threshold â¨Iâ© just above the irradiance local peaks during MY34 and MY35.” The authors should define the threshold â¨Iâ© when introducing the EUV flux levels in Line 316-322.
Line 537-540: “As the exosphere expands with increasing EUV flux, the obstacle to the solar wind flow grows in size, with the bow shock and IMB both swelling up. This is illustrated in Fig. 9 by the dashed bow shock curves of Simon Wedlund et al. (2022b) and how they compare to the fixed curves of Hall et al. (2019).” The bow shock and IMB will both swell up with increased EUV flux. However, in Fig. 9, the dashed lines only show the expanding bow shock, but the modeled boundary of IMB is fixed. The authors should describe it more clearer.
Figs. 8, 9 & 11: As we can see from those figures, the detection probability P may reach artificially low values, especially in the region in front of the modeled bow shock and in the tail. However, when calculating the difference from the total detection probability âP/Ptot, the data coverage is quite different among these figures. Do the authors remove the small value when plotting the âP panels? What is the criteria the authors chose to remove these data points? Why not discard the data points with low P since they make little sense?
Minor Issues:
Line 8-9: I suppose that the time range of the dataset should be corrected from “February 2020” to “February 2021”.
Line 314-315: “For reference, MY32 = [] … .” There is an error in the representation of parentheses.
Line 602: “… (see also Fig. 7g and Table 3).” There is no Fig. 7g. Please check it.
Line 628-629: Add “are used” at the end of the sentence.
Citation: https://doi.org/10.5194/egusphere-2022-634-RC2 -
AC2: 'Reply on RC2', Cyril Simon Wedlund, 05 Feb 2023
Dear reviewer,
We would like to thank the two anonymous referees for their constructive comments, questions and suggestions. Please find our answers below, with all the points raised during the review addressed in the PDF attached.Throughout, our responses are marked as “AC2” and shown in italic, whereas all other instances (non-italic text) are the original reviewer comments and questions.
CSW et al. 05 February 2023
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AC2: 'Reply on RC2', Cyril Simon Wedlund, 05 Feb 2023
-
AC4: 'Comment on egusphere-2022-634', Cyril Simon Wedlund, 03 Mar 2023
Dear Editor,
This paper is the first in a series of papers on the statistical distribution of mirror mode-like structures at Mars and Venus. The second paper (Volwerk et al. 2023) is available here: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-645/ and is currently under revision in Annales Geophysicae.
For the time being, our revised manuscript has thus this one reference as "submitted" in the text (Volwerk et al. 2023) which appears a total of three times to refer to the fact that we have a corresponding Venus study. Thus, if necessary and to speed up acceptation of our current manuscript, we can remove this reference altogether without losing anything to our current paper at Mars. We leave it to the editor to decide which is best in this case.
Kind regards,
Cyril Simon WedlundCitation: https://doi.org/10.5194/egusphere-2022-634-AC4
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-634', Anonymous Referee #1, 30 Aug 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-634/egusphere-2022-634-RC1-supplement.pdf
-
AC1: 'Reply on RC1', Cyril Simon Wedlund, 05 Feb 2023
Dear reviewer,
We would like to thank the two anonymous referees for their constructive comments, questions and suggestions. Please find our answers below, with all the points raised during the review addressed in the PDF attached.Throughout, our responses are marked as “AC1” and shown in italic, whereas all other instances (non-italic text) are the original reviewer comments and questions.
Best regards,
CSW et al. 05 February 2023-
AC3: 'Reply on AC1', Cyril Simon Wedlund, 05 Feb 2023
We discovered a typo in our response to Reviewer 1, on page 6, "Line 422" of the PDF. "10/7" should read instead of "10/3", obviously (70% of the orbit is taken into account, hence a factor 1.5 of multiplication). The text should be:
"AC1: This is a very good point which we had originally missed, and we are grateful to the reviewer for it. The histogram of Fig. 6 assumes a full day of observation, but because we have removed the events in the solar wind and MAVEN spends about 30% of its time on average in the solar wind (see, for example, the Figure 1 of Simon Wedlund et al. 2022c), all numbers should be compensated for this lack of temporal coverage by at least an equal number (multiplied by a factor 10/7 ~ 1.5 at least). To clarify this, we first add some statistics in Table 3 (see below). [...]"
Citation: https://doi.org/10.5194/egusphere-2022-634-AC3
-
AC3: 'Reply on AC1', Cyril Simon Wedlund, 05 Feb 2023
-
AC1: 'Reply on RC1', Cyril Simon Wedlund, 05 Feb 2023
-
RC2: 'Comment on egusphere-2022-634', Anonymous Referee #2, 28 Dec 2022
Mirror Modes (MMs) are often observed in the magnetosheath of many solar system objects, like Earth, Venus, Mars and comets. This paper presents the statistical maps of mirror mode-like (MM) structures in the magnetosheath of Mars based on the magnetometer data only of MAVEN from November 2014 to February 2021 (MY32-MY35). Based on the magnetic field-only criteria and two mitigation strategies, 176,041 MM-like structures are detected in their final database. Then, they analyze the characteristics and calculate the detection probabilities of MM-like structures with respect to several controlling parameters (including Mars Years, EUV flux and Mars season, Ls) and map them in the magnetosheath of Mars. The results indicate MM-like structures appear in two main regions: behind the shock and close to the induced magnetospheric boundary. And the detection probabilities are higher with low solar EUV flux, which contradicts the prospect, explained by two combining effects: plasma beta effects and non-gyrotropy of pickup ion distributions. The detection method and mitigation strategies are well described and the properties of MMs are well shown by plenty of figures. Before I recommend accepting to publication in AG, below comments/suggests needs to address.
As shown in the introduction, MMs likely share a common ancestor with magnetic holes (MHs); statistical characteristics of magnetic holes have already been analyzed in the Martain magnetosheath. For instance, Huang et al. (2021, ApJ, 922:107) analyzed the distribution and parameter characteristics of kinetic-size magnetic holes (KSMHs) in the Martain magnetosheath using MAVEN’s data and tries to explain the mechanism of KSMHs as electron vortex. These results may also shed light on the mechanism of MMs. The authors should try to compare the properties between MMs and MHs to figure out the relationship between these structures and their mechanisms and their differences.
Line 185-186: “moreover this ensures that rotations could be calculated for trains of MM-like structures for which the 2-min windowed background magnetic field values would be representative.” This sentence is complicated and vague.
Line 245-250: “Conversely, we also expect the method to keep structures that are likely not MMs but situated in the magnetosheath (with B and N in phase).” What do the authors want to express by this sentence? Besides, the authors try to keep the isolated structures out of the final database to make the results accurate. Now that, what does this sentence “As a consequence, on this criterion only (isolated structure), the frequency of MM-like detections in our final database could be underestimated by at least 10%.” mean? Should the isolated structures be included in the database or not?
Line 277-278: “…, which we expect to be about 25%, as evaluated from visual comparisons in a subset of events (see Figs. 1 and 2).” How do the authors evaluate the extent of the underestimation and from which subsets of events?
Line 392-396: “Secondly, the two detection methods differ significantly: our B-field-only criteria detection permits us to capture trains of short events with 1-s resolution at the expense of an ambiguity in the nature of the detected structure, whereas Ruhunusiri et al. (2015) used wave analysis techniques based on transport ratios with a cruder time resolution (4–8 s with a Fourier transform on consecutive 128 s intervals).” The authors try to compare the detection probabilities between this work and Ruhunusiri et al. (2015) and explain the lower estimate due to the detection method. However, the lower resolution in Ruhunusiri et al. (2015) could also lead to the omission of smaller structures, resulting in a lower estimate for their results. It’s hard to make a comparison and draw a conclusion in this way.
Line 427-428: “…, we cannot compare absolute detection numbers with the other MYs without first normalising to the spacecraft’s residence time during that period.” The authors could try to calculate the detection probabilities of each Mars year, so far as the absolute detection numbers and the spacecraft’s residence time can be obtained, as shown in Fig. 8.
Table3: "NMM represents the total number of MM-like events found (equivalent to a duration in s because of the magnetometer resolution of 1 s)”.
Line 419-421: “On average throughout MY32 to MY35 with MAVEN, we find â¨Nâ© = 68±43 structures per day (ignoring single isolated 1-s events, see Sect. 2.2.2) fulfilling the criteria of Table 1.”
Line 429-430: “Finally, if we assume that most structures last 5–10s on average, we end up with 68/10–68/5 ≈ 7–14 MMs/day in Mars’ magnetosheath.”
What’s the definition of an MM-like event, a structure and a MM? Are they the same or not? What is the relationship between them?
Line 445: “… , with the threshold â¨Iâ© just above the irradiance local peaks during MY34 and MY35.” The authors should define the threshold â¨Iâ© when introducing the EUV flux levels in Line 316-322.
Line 537-540: “As the exosphere expands with increasing EUV flux, the obstacle to the solar wind flow grows in size, with the bow shock and IMB both swelling up. This is illustrated in Fig. 9 by the dashed bow shock curves of Simon Wedlund et al. (2022b) and how they compare to the fixed curves of Hall et al. (2019).” The bow shock and IMB will both swell up with increased EUV flux. However, in Fig. 9, the dashed lines only show the expanding bow shock, but the modeled boundary of IMB is fixed. The authors should describe it more clearer.
Figs. 8, 9 & 11: As we can see from those figures, the detection probability P may reach artificially low values, especially in the region in front of the modeled bow shock and in the tail. However, when calculating the difference from the total detection probability âP/Ptot, the data coverage is quite different among these figures. Do the authors remove the small value when plotting the âP panels? What is the criteria the authors chose to remove these data points? Why not discard the data points with low P since they make little sense?
Minor Issues:
Line 8-9: I suppose that the time range of the dataset should be corrected from “February 2020” to “February 2021”.
Line 314-315: “For reference, MY32 = [] … .” There is an error in the representation of parentheses.
Line 602: “… (see also Fig. 7g and Table 3).” There is no Fig. 7g. Please check it.
Line 628-629: Add “are used” at the end of the sentence.
Citation: https://doi.org/10.5194/egusphere-2022-634-RC2 -
AC2: 'Reply on RC2', Cyril Simon Wedlund, 05 Feb 2023
Dear reviewer,
We would like to thank the two anonymous referees for their constructive comments, questions and suggestions. Please find our answers below, with all the points raised during the review addressed in the PDF attached.Throughout, our responses are marked as “AC2” and shown in italic, whereas all other instances (non-italic text) are the original reviewer comments and questions.
CSW et al. 05 February 2023
-
AC2: 'Reply on RC2', Cyril Simon Wedlund, 05 Feb 2023
-
AC4: 'Comment on egusphere-2022-634', Cyril Simon Wedlund, 03 Mar 2023
Dear Editor,
This paper is the first in a series of papers on the statistical distribution of mirror mode-like structures at Mars and Venus. The second paper (Volwerk et al. 2023) is available here: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-645/ and is currently under revision in Annales Geophysicae.
For the time being, our revised manuscript has thus this one reference as "submitted" in the text (Volwerk et al. 2023) which appears a total of three times to refer to the fact that we have a corresponding Venus study. Thus, if necessary and to speed up acceptation of our current manuscript, we can remove this reference altogether without losing anything to our current paper at Mars. We leave it to the editor to decide which is best in this case.
Kind regards,
Cyril Simon WedlundCitation: https://doi.org/10.5194/egusphere-2022-634-AC4
Peer review completion
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Cyril Simon Wedlund et al.
Cyril Simon Wedlund et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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