Even moderate geomagnetic pulsations can cause fluctuations of <i>fo</i>F2 frequency of the auroral ionosphere

Yagova, Nadezda; Kozlovsky, Alexander; Fedorov, Evgeny; Kozyreva, Olga

doi:https://doi.org/10.5194/angeo-39-549-2021

Articles | Volume 39, issue 3

https://doi.org/10.5194/angeo-39-549-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/angeo-39-549-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 39, issue 3

Regular paper

|

16 Jun 2021

Regular paper |

| 16 Jun 2021

Even moderate geomagnetic pulsations can cause fluctuations of foF2 frequency of the auroral ionosphere

Nadezda Yagova, Alexander Kozlovsky, Evgeny Fedorov, and Olga Kozyreva

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Final revised paper (published on 16 Jun 2021)
Supplement to the final revised paper
Preprint (discussion started on 13 May 2020)
Supplement to the preprint

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Referee's Report', Anonymous Referee #1, 29 May 2020
- AC2: 'Answer to referee-1 report', Nadezda Yagova, 14 Sep 2020
RC2: 'Review feedback on the manuscript', Anonymous Referee #2, 19 Aug 2020
- AC1: 'Answer to referee-2 report', Nadezda Yagova, 14 Sep 2020

Peer-review completion

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

ED: Reconsider after major revisions (further review by editor and referees) (16 Sep 2020) by Georgios Balasis

AR by Nadezda Yagova on behalf of the Authors (10 Nov 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Nov 2020) by Georgios Balasis

RR by Anonymous Referee #1 (10 Dec 2020)

Suggestions for revision or reasons for rejection

The paper has improved a lot through the latest revision. My comments have been addressed adequately. The science content is now much more sound than in the previous version. The relations found between the occurrence of coherent fluctuations in geomagnetic field and foF2 with the parameters investigated are rather weak. According to 10b, the improvement in the frequency correspondence (absolute difference) between magnetic and foF2 pulsations for the coherent events is less than 5% compared to the same difference calculated for all events. This needs some explanation and discussion.
The relative occurrences of the coherent events (vs different parameters) are presented at two levels of coherence. For me, it seems unnecessary and rather confusing then helpful. I suggest to keep only the distributions at the gamma_squared = 0.5 level. At higher level, the occurrence rate of coherent events remains mostly below 5%. It just means that highly coherent events are rare.
However, the main problem with the current version of the paper is that it is still very difficult to read.
Firstly, because the organisation of the paper is not reader-friendly. Section 2.3 (Pre-processing), especially from line 143 is a mere listing of the spectral, statistical quantities applied later in the paper. Without giving examples, it is difficult to follow what is the function and purpose of the different quantities in the data analysis, and also the definition of the quantities is sometimes unclear. (e.g. “the fraction of intervals Rγ with over-threshold maximal γ2 is presented”).
Secondly, because of the confusing use of the terminology and notation. Different terms are used for the same thing, however, it is not explained to the readers that they refer to the same thing. E.g. “a fraction” (that is itself very confusing) is also called “coherent ratio” in the meaning of ‘relative occurrence of coherent events’. Another example: “meridional distribution” vs. “south-to-north ratio” in the meaning of ‘frequency dependence of the south-to-north ratio’ or ‘south-to-north spectral ratio. It is also confusing, that the same letters are used to denote very different things. E.g. P means probability, PSD, and also PSD peak (although in the latter- P_f,b - meaning it is always referred to as PSD maximum in the article. ‘PSDmax’ or similar would be more natural and understandable choice for the latter). Some indices seems unnecessary, e.g. since PSD (except for the very last figure) is only calculated from magnetic signals, so P_f,b or PSD_f,b could be simply PSDmax. Both ‘F’ and ‘f’ are used for frequency. Phi denotes both phase and magnetic latitude. ‘R’ stands for PSD ratio and relative occurrence, etc.
Finally, the English of the paper is still very poor. I add a list of some of the typos I found. This list is very far from being complete!

27 filed > field
73 …AE > … AE indices.
75 :: > :
78 at, in > between, at
106 foF2 which > foF2 for which the
136 for the > for
152 at > of
161 the its > its
201 the distributions of the parameters of foF2 variations with the magnetic local time > MLT-dependence of the occurrence rate
202 occurrence of foF2 interval [confusing phrase]
204 a fraction of > the occurrence rate of coherent events [?]
205 bb maximum: what is bb?
205, 206: the noon > noon
Fig 11 in the legend 1 should be 2 or the text should be adjusted
242 which it is [?]
253: 3 times higher: I cannot see what you mean
261: A difference … is seen: I cannot see it
261 probablity of the … interval [?]
Fig 13 R_gamma : the Greek letter should be used here

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RR by Anonymous Referee #2 (24 Dec 2020)

Suggestions for revision or reasons for rejection

This revised manuscript explores the statistical behaviour of ionospheric variations in the frequency range of 1 -5 mHz and simultaneous low-frequency geomagnetic pulsations observed at auroral latitudes during periods of quiescence but also under moderately disturbed geomagnetic conditions. Using a newly developed method for the automated detection of ionospheric F2 region’s critical frequency, foF2, from ionograms, Yagova et al. investigated time intervals where fluctuations of the ionosphere’s FoF2 frequency are accompanied by similar temporal variations of the magnetic field’s northward component as this has been measured by ground magnetometers. They identified several cases of high coherence indicating a convincing relationship between low-frequency geomagnetic pulsations and the modulation of the ionosphere’s F2 layer. They also looked into favourable solar wind conditions to find that solar wind pressure pulses, known to excite magnetospheric ULF waves, are among the possible drivers of both geomagnetic pulsations and particle modulation.

The presentation of their methodology and analysis’ results have greatly helped the support of the manuscript as well as its readability. This revised manuscript has a few issues that I would like to see addressed to the editor’s satisfaction before I could recommend publication of this manuscript.

In line 1 of the Abstract, it would be more convenient for the reader to know that the coordinates provided for the Sodankyla Geophysical Observatory are the geographical coordinates rather that to have to look this up in Table 1.

In line 3 of the Abstract and throughout the manuscript, the authors talk about Pc5/Pi3 waves. I would caution the authors against referring to Pc5 and Pi3 waves together, when Pc5 waves are considered to have a sinusoidal wave form and last longer than Pi3 waves that have an irregular wave form. Pi3 waves can be the ground counterpart of Pc5 waves with moderately high-m numbers observed by spacecraft, as it was found by Vaivads et al (2001), but this study is centred around geomagnetic pulsations observed on the ground. The authors cite several published results of research carried out with focus on either Pi3 or Pc5 waves. Among others, Kleimenova et al. (2002) showed that auroral substorms influence Pi3 activity but Baker et al. (2003) isolated Pc5 waves whose amplitude did not grow nor was damped as is the case of irregular pulsations for their study of Pc5 waves. Furthermore, Posch et al. (2003) adopted a ULF index that allows to minimise the power contribution of large, irregular pulsations along with the total ULF wave power which may include the substorm counterpart of ULF waves. Although, Pc5 and Pi3 waves’ frequency falls in the same range, adequate justification for the choice to consider the two types of waves together needs to be provided.

In line 77 of Section 2.1, the authors note that geomagnetic pulsations are searched for in the BX component of the magnetic field measured by ground magnetometers (it should read “Bx”). Later in line 119 of Section 2.3, the symbol bx is used for variations of the same component. However, it is not made clear how these variations have been identified. Has a mean value been calculated that corresponds to the Earth’s main magnetic field, and variations been defined as deviations from this mean? Has a different approach been adopted for the derivation of magnetic field variations?

In line 79 of Section 2.1, the authors refer to Table 2 that includes a list of more than 80 intervals that have been selected for further analysis. (It is redundant to provide the same table in the Supplement.) In Section 2.3, these intervals where foF2 has been retrieved utilising the new methodology have been divided into four groups. Please add group 5 to the list which has not been introduced until in Section 3.1.2 and point out the assumptions that have been used in statistical analysis of data covering time intervals of varying length unambiguously. It is also strongly recommended to provide sufficient details of the grouping of foF2 frequency data in 2764 overlapping intervals, as this is mentioned in line 151, to prove the validity of the statistics. For instance, it is not so clear how it was concluded that foF2 frequency fluctuations and geomagnetic pulsations are more likely to occur coherently in the recovery phase of moderate geomagnetic storms.

In the last two paragraphs of Section 2.3, the authors provide details of the power spectral density calculations and cross-spectral analysis. It is, however, not clear whether the Blackman-Tukey correlogram/periodogram analysis has also been used for the calculation of PSD in the Bx and By component.

In line 171 of Section 3.1.1, it would more correctly read “Peak amplitudes of geomagnetic pulsations and foF2 variations are about 8 nT and 0.05 MHz.” and in line 183, “Their peak-to-peak amplitude was about 0.7 nPa …”. In line 178, it should read “…start time of the interval (12:20 UT).”

On page 16, please consider adding a colour bar in Figure 1 with the three ionograms from the Sodankyla ̈Geophysical Observatory provided as examples. This would also help make clearer the first of the two criteria set for the automated detection of foF2 and specifically, the condition that the intensity of reflection should fulfil. Please consider providing the units of measurement in line 97 of Section 2.2 for the lower value of the intensity.

Please note that there are numerous typos making it necessary to carefully revise the manuscript in terms of spelling and punctuation as well as language. For example, in line 6 of the Abstract, the authors must mean “automated retrieval of foF2, the critical frequency of the F2 layer from ionograms.” In line 27, “filed line resonances” should be “field line resonances”. In line 37, the comma after “observed oscillations is, …” should be deleted. In line 56, it is not clear to me and perhaps the reader what the term “principle opportunity” means. In line 66, “ionosond” should be changed to “ionosonde”. In line 83, it would more correctly read “variability of the intensity of reflected signals, background noise, sporadic layers and irregularities, broadcast interference, etc.” In line 88, it would more correctly read “near linear growth” and, in line 89, “Lorentzian function” instead of “Lorentzian shape function” which makes one think of spectral line shape. In line 164, it should read “γb2 = 0.64, γ2 > 0.375”.

Lastly, the format of citations should be revised. For example, in line 25, “(Wright et al., 1997) should be changed to “Wright et al. (1997)” and in line 47, “(Pilipenko et al. 2014b)” should be “Pilipenko et al. (2014b)”.

References

Saito (1978), Long-period irregular magnetic pulsation, Pi3, Space Science Reviews, doi: 10.1007/BF00173068

Vaivads et al. (2001), Correlation studies of compressional Pc5 pulsations in space and Ps6 pulsations on the ground, Journal of Geophysical Research, doi: 10.1029/2001JA900042

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ED: Reconsider after major revisions (further review by editor and referees) (08 Jan 2021) by Georgios Balasis

AR by Nadezda Yagova on behalf of the Authors (10 Feb 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (16 Feb 2021) by Georgios Balasis

RR by Anonymous Referee #2 (14 Apr 2021)

Suggestions for revision or reasons for rejection

There are still several issues, including the following:

In lines 2 and 3, the frequency range of geomagnetic pulsations examined in this study is first mentioned. Specifically, it should read “…with frequencies close to those of geomagnetic pulsations in the Pc5-6/Pi3 frequency band (1 – 5 mHz).” Later, in line 6, it should read “... As a rule, the Pc5-6/Pi3 frequency band …”. The same notation should be maintained throughout the manuscript.

In line 32, it would more correctly read “ … devoted to Pc5 wave signatures in total …”.

In lines 55 to 57, it should read “…six years of Van Allen Probes measurements confirmed the influence of ULF waves in Pc4 and Pc5 frequency ranges on electrons with energies up to the order of 10^2 eV with maximum occurrence around L from 5.5 to 7 (Ren et al., 2019).”

In lines 133 and 134, what is written in the previous lines 131 and 132 is essentially repeated.

In lines 135 to 137, the two indices, AE and Dst, as well as parameters of the solar wind considered in the present analysis are repeated. Τhey were first introduced in Section 2.1.

In line 138, it should read “ …analysis, all intervals were classified …”.

In line 141, it should read either “…spectra of geomagnetic pulsations …” or “…spectra of geomagnetic field variations …”. The terms “geomagnetic field variations” and geomagnetic pulsations should be adopted in the place of “geomagnetic variations” which it is not clear to me - and perhaps the reader - to what it refers. However, it is often used in this version of the manuscript.

In line 142, should it read “…intervals, for which spectra of foF2 variations can be calculated (ΔfoF2 intervals …”?

And later, in line 144, should it read “…coherent ΔfoF2-bx intervals, …” even though the explanation of ΔfoF2 and bx are not provided earlier that the next Section 3.1? It is the coherence between filtered time series of the foF2 frequency and the meridional component of the geomagnetic field B that has been calculated, if I have not confused the notations.

Furthermore, the organisation of Section 2.3 could be improved if the first introductory paragraphs (in the current version of the manuscript, it is not clear whether there are two, three or more paragraphs from the beginning until line 137) were followed by details of the data analysis carried out which are presented in lines 152 to 170. The classification of intervals examined that is currently found between lines 138 and 145 should be placed before the statistics for these intervals presented in lines 160 to 162.

In line 174, it would more correctly read “foF2 frequency and geomagnetic field variations” and later, in line 177, “A high pass filter with cut-off frequency at 0.8 mHzThe time series in Figures 3 and 6 are filtered …”.

In line 263, it chould read “Statistics on ΔfoF2 and bx fluctuations related to different levels of geomagnetic activity are presented in Figure 13. Left panels (13a, c) present the occurrence distribution for all, ΔfoF2 and coherent ΔfoF2-bx intervals (groups 1, 3 and 4)…”.

In Figure 13, would it be possible to add labels to tick marks other than 100 and 1000 which are currently visible in plots 13c and 13d so that it is easier to follow the description of the statistics in Section ?

This list of issues identified is far from inclusive but hopefully indicative of the manuscript’s poor readability.

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ED: Publish subject to minor revisions (review by editor) (19 Apr 2021) by Georgios Balasis

AR by Nadezda Yagova on behalf of the Authors (28 Apr 2021) Author's response Author's tracked changes Manuscript

ED: Publish as is (17 May 2021) by Georgios Balasis

AR by Nadezda Yagova on behalf of the Authors (18 May 2021) Author's response Manuscript

Short summary

We present a study of ultralow-frequency waves in the ionosphere and on the ground. These waves are very slow (their periods are about several minutes). They are registered on the ground as geomagnetic pulsations. No simple dependence exists between geomagnetic and ionospheric pulsations. Here we study not only selected pulsations with very high amplitudes but also usual pulsations and try to answer the question, which pulsation parameters are favorable for modulation of the ionosphere?