the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Oct 2024
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: open (until 18 Dec 2024)
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RC1: 'Comment on egusphere-2024-2052', Anonymous Referee #1, 18 Nov 2024
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“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
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