the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
No statistical link between proton aurora and Pc1 pulsations in the high-latitude dayside using ground-based measurements
Abstract. In order to test the hypothesis that EMIC waves are responsible for the acceleration of auroral protons, we have used spectrograph measurements of proton aurora over Svalbard alongside co-located magnetometer measurements of Pc1 pulsations. No evidence of a link between proton aurora and Pc1 waves was found by three different methods. Firstly, accelerated protons and Pc1 pulsations have no coincident occurrence. Secondly, the proton energy spectrum does not change between Pc1 activity and quiet times. Finally, no imprint of the EMIC wave is found in periodicity of the intensity and blue-shift of the proton H-α line, unlike in flickering electron aurora where intensity fluctuations are caused by EMIC waves. We find no evidence that EMIC waves are the mechanism responsible for accelerating auroral protons in the high-latitude dayside, at least based on the considered ground-based data of proton aurora and magnetic Pc1 pulsations.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2024-2052', Anonymous Referee #1, 18 Nov 2024
“No statistical link between proton aurora and Pc1 pulsations in the high-latitude dayside using ground-based measurements.” by Rowan Dayton-Oxland et al.
The manuscript presented a statistical relationship between proton auroras and Pc1 wave activities at KHO near the cusp location. There are some ideas for proton precipitation, but the authors focused on the effects of pitch angle scattering by EMIC waves in the magnetosphere through the statistical results. The magnetic field line curvature scattering of protons should be a major factor at higher latitudes (e.g., Ma, L. et al., JGR Space Physics, 127, e2022JA030843, 2022). However, the authors do not discuss and analyze whether the observation location is inside or outside the isotropic boundary (IB). The authors should classify the location as inside or outside the IB in order to discuss the effects of pitch angle scattering by EMIC waves without the effects of the field line curvature scattering. Therefore, this manuscript, which concludes that there is no effect of EMIC waves on proton aurora generation, is a major missing discussion because it does not clearly and quantitatively distinguish whether the events analyzed in this study are outside or inside the IB. Therefore, I recommend that the authors should resubmit the manuscript with significant modifications. Please see detailed comments below.
[Major comments]
1) Without statistically comparing Pc1 and proton aurora at the observation site outside or inside from the IB for all events, it is quantitatively difficult to distinguish between the effects of field line curvature scattering and pitch angle scattering by EMIC waves. Please add the statistical results of a ratio Rc/rho, where Rc is the curvature radius of the field line, rho is the effective particle gyroradius (see, Sergeev et al., JGR, 98(5), pp.7609-7620, 1993), it would be useful for the additional discussion.
2) Pc1 waves can easily propagate thousands of kilometers horizontally through the ionospheric duct. Therefore, taking into account the effects of the ionospheric duct, the authors should classify Pc1 waves as the ionospheric penetration from the magnetosphere along the magnetic field lines at KHO, or as horizontally propagating Pc1 waves.
These two important issues for the relationship between the proton aurora and Pc1 waves, which do not take into account the effects of horizontal propagation and the location of the IB, cannot verify the presence or absence of the influence of pitch angle scattering by the EMIC waves. We hope that these comments will be useful for your further research.
Citation: https://doi.org/10.5194/egusphere-2024-2052-RC1 -
RC2: 'Comment on egusphere-2024-2052', Anonymous Referee #2, 22 Nov 2024
This paper statistically examines the correlation between proton auroras and Pc1 waves observed at the same ground locations. The authors found no correlations between (1) proton flux, (2) proton energy spectrum, (3) intensity of H-alpha lines, and Pc1 activity. Although all the results in the paper indicate that there is no clear evidence for a relationship between Pc1 waves and proton auroras, there are still some methodological points that need to be clarified and considered to draw a definitive conclusion.
Major comments
1) Regarding the contingency table (Table 1):
The occurrence rate of proton auroras is much higher than that of Pc1 wave events. Thus, it is somewhat reasonable to conclude that the majority of proton auroras are not driven by (or correlated with) Pc1 waves. However, it is still possible that Pc1 waves are highly likely to drive proton auroras when they occur. Considering the low occurrence rate of Pc1 waves, the difference in numbers between p11 and p01 seems large. Therefore, it should not be definitively stated that there is no link between Pc1 waves and proton auroras.
Additionally, the authors should consider a more lenient contingency condition for identifying events. Counting events strictly based on simultaneous observations seems overly restrictive. It is plausible that proton precipitation and wave propagation occur at slightly different times due to various factors, including differing propagation times. Even wave activities coincidentally observed in space and on the ground at conjugate locations can have different start times and durations.
2) Potential statistical bias:
In L100, the authors mention excluding Pc1 events contaminated by auroral noise. How much time (or how many Pc1 events) was excluded from the study? If this represents a large portion of the dataset, the statistics may be biased. Moreover, if the exclusion of wave events is related to auroral activities, the authors should handle the dataset carefully to avoid introducing bias into the analysis.
Minor comments
L10: Provide the energy range of these energetic protons.
L18: Provide the frequency range of Pc1 waves.
L24: Instabilities causing EMIC waves are not a mixture of hot and cold plasmas. They are driven by either anisotropy or ion beam instabilities.
L58: Approximating the L-shell coverage of the KHO observatory would be helpful for mapping this process to magnetospheric activities.
L78: Why is this event considered “unstructured”?
L88: The identification method for Pc1 waves is not described in Appendix A. Please explain how the authors processed the search coil data and identified wave activities.
L100: The authors mention that data recorded during daylight were eliminated, but later state that data from 6–18h MLT were considered. This paragraph should be rewritten for clarity. Additionally, the authors should specify how much data were excluded due to daylight or bright cloud, as this could significantly affect the statistics, as noted in the second major comment.
L103: Clarify the meaning of “correlation.” Does this refer to the coincidence of the two phenomena?
L108: Elaborate on why an odd ratio of 1.856 is not significant. From my understanding, 1.923 is the maximum odd ratio from 1,000 subsample trials. If true, this value may lack significance, as it could vary depending on the number of subsamples or sampling runs. If this is incorrect, please provide a clear explanation of how the threshold was determined. The odd ratio’s statistical significance should also be considered, as it would approach 1 if the two phenomena were entirely independent with a sufficiently large sample size.
L114: Explain how the 200 minutes of data were determined. Using only 200 minutes of proton aurora data without Pc1 waves represents significant under-sampling and could introduce statistical bias.
L128: Change "proton events" to "proton aurora events."
L130: Why is a 1–10 s periodic signal required? Is this related to the Pc1 frequency?
L132: The authors state that they used FFT to analyze signal periodicity but do not present any FFT results in the paper.
L161: Could the authors provide references or background information for this process? To my knowledge, this complicated process is unlikely to result solely from linear or quasi-linear wave-particle interactions.
L175: If the alternative explanations also suffer from the same issue (transience), they cannot be considered valid alternatives.
L187: The results do not indicate that EMIC waves are not an acceleration mechanism. EMIC waves can still accelerate ions, but they are not the governing mechanism responsible for the majority of proton auroras.
Citation: https://doi.org/10.5194/egusphere-2024-2052-RC2
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