the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2025
A comparison of methods to compute the rate of horizontal geomagnetic field variation
Abstract. The rate of change of the horizontal external magnetic field is often used as a proxy for space weather activity and in particular for estimating geomagnetically induced currents (GICs) in high voltage power grids. This paper compares two commonly adopted methods for computing this rate of change: (1) the difference between consecutive measurements in the magnitude of the horizontal magnetic field, H′, and (2) the combined difference in the magnitude in the northward and eastward directions, usually denoted R. We find that there can be an absolute difference in the calculations between the two methodologies exceeding 100 nT/min during storm times for observatories in the sub-auroral zone, demonstrating that the choice between R and H′ can make a significant difference to any GIC estimate. We also note an observable difference between the two methodologies during quiet times when the measurements are made close to the agonic line, though this difference does not have a significant impact on the efficacy of either of the two methodologies for GIC studies. Future studies should consider carefully the choice of geomagnetic indicators for estimation of GICs.
- Preprint
(4323 KB) - Metadata XML
- BibTeX
- EndNote
Status: final response (author comments only)
-
CC1: 'Comment on egusphere-2025-2857', Barbara Page, 07 Jul 2025
Line 56 replace "there are there are several methods that can be" with "several methods can be"
Citation: https://doi.org/10.5194/egusphere-2025-2857-CC1 -
CC2: 'Comment on egusphere-2025-2857', Bruce Tsurutani, 11 Jul 2025
Review of “A Comparison of Methods to Compute the Rate of Horizontal Geomagnetic Field Variation” by Fielding, Livermore, Beggan, Whaler and Richardson
The authors are to be commended for doing careful analyses, however when reading the paper one is continually asking the question why are only Bn and BE considered? Maybe those are the dominant magnetic components during quiet intervals, but what about magnetic storm times? I think the authors have not kept up with the current literature. I suggest that they read several recent works and rethink their method of analyses. See Geomag. Aer., 2024, 64, 6, 833-844; SW, 21, e2022SW003383, 2023. https://doiorg/10.1029/2022SW003383; Nat. Port. Sci. Rpts, 14:25074, https://doi.org/10.1038/s41598-024-76449-z; J. Atmos. Sol.-Terr. Phys., 261, 2024. It is clear from these papers that the magnetic perturbations can occur quickly and in all directions during magnetic storms. These papers should be referenced and mentioned in the introduction section of the paper.
In the Introduction Section, the references quoted are no. primary papers. I suggest that the authors do some basic literature search and come up with some more basic references.
Line 15, probably an early reference to CMEs (and sheaths) is JGR, 93, A8, 8519-8531, 1988.
Line 16. Two good references for solar energetic particles are: SSR, 90, 413–491,1999, doi:
10.1023/A:1005105831781 and JGRSP 2024 129, e2024JA032622. https://doi.org/10.1029/2024JA032622
Line 18. Better references are: Phys. Rev. Lett., 6, 47, 1961 and JGR, 77, 16, 2964-2970, 1972,
Line 19. A better reference for the enhancement of the radiation belts is JGR 76, 16, 3587-3611, 1971.
Line 20. There has to be an earlier and better reference for the aurora?
Line 21. A reference for substorms is needed here. It is PSS 12(4), 273–282. https://doi.org/10.1016/0032-0633(64)90151-5
Line 25. Add reference JSWSC, 2021, 11, 23, https://doi.org/10.1051/swsc/2021001. This paper notes that the biggest GICs at the Mantsala Norway pipeline during a 21 year study were detected during the Halloween 2003 magnetic storms. I will come back to this point later.
Line 41, the time derivative of the magnetic field needs a reference. See GRL 2014, 41, doi:10.1002/2013GL058825.
Lines 164-166. There are several “Halloween storms”. Please be specific. See the reference for line 25. The two Halloween magnetic storms had the highest GICs in the 21 years of Mantsala pipeline data. So what does this tell you about future efforts for finding a proxy for GICs? What can you do to improve your model?
In the Introduction you need to inform the readership that the biggest GICs are associated with magnetic storms. Since that is the case you need to focus your study on field variations that are applicable to storm intervals.
Citation: https://doi.org/10.5194/egusphere-2025-2857-CC2 -
RC2: 'CC2 again as RC', Bruce Tsurutani, 15 Aug 2025
Review of “A Comparison of Methods to Compute the Rate of Horizontal Geomagnetic Field Variation” by Fielding, Livermore, Beggan, Whaler and Richardson
The authors are to be commended for doing careful analyses, however when reading the paper one is continually asking the question why are only Bn and BE considered? Maybe those are the dominant magnetic components during quiet intervals, but what about magnetic storm times? I think the authors have not kept up with the current literature. I suggest that they read several recent works and rethink their method of analyses. See Geomag. Aer., 2024, 64, 6, 833-844; SW, 21, e2022SW003383, 2023. https://doiorg/10.1029/2022SW003383; Nat. Port. Sci. Rpts, 14:25074, https://doi.org/10.1038/s41598-024-76449-z; J. Atmos. Sol.-Terr. Phys., 261, 2024. It is clear from these papers that the magnetic perturbations can occur quickly and in all directions during magnetic storms. These papers should be referenced and mentioned in the introduction section of the paper.
In the Introduction Section, the references quoted are no. primary papers. I suggest that the authors do some basic literature search and come up with some more basic references.
Line 15, probably an early reference to CMEs (and sheaths) is JGR, 93, A8, 8519-8531, 1988.
Line 16. Two good references for solar energetic particles are: SSR, 90, 413–491,1999, doi:
10.1023/A:1005105831781 and JGRSP 2024 129, e2024JA032622. https://doi.org/10.1029/2024JA032622
Line 18. Better references are: Phys. Rev. Lett., 6, 47, 1961 and JGR, 77, 16, 2964-2970, 1972,
Line 19. A better reference for the enhancement of the radiation belts is JGR 76, 16, 3587-3611, 1971.
Line 20. There has to be an earlier and better reference for the aurora?
Line 21. A reference for substorms is needed here. It is PSS 12(4), 273–282. https://doi.org/10.1016/0032-0633(64)90151-5
Line 25. Add reference JSWSC, 2021, 11, 23, https://doi.org/10.1051/swsc/2021001. This paper notes that the biggest GICs at the Mantsala Norway pipeline during a 21 year study were detected during the Halloween 2003 magnetic storms. I will come back to this point later.
Line 41, the time derivative of the magnetic field needs a reference. See GRL 2014, 41, doi:10.1002/2013GL058825.
Lines 164-166. There are several “Halloween storms”. Please be specific. See the reference for line 25. The two Halloween magnetic storms had the highest GICs in the 21 years of Mantsala pipeline data. So what does this tell you about future efforts for finding a proxy for GICs? What can you do to improve your model?
In the Introduction you need to inform the readership that the biggest GICs are associated with magnetic storms. Since that is the case you need to focus your study on field variations that are applicable to storm intervals.
Citation: https://doi.org/10.5194/egusphere-2025-2857-RC2
-
RC2: 'CC2 again as RC', Bruce Tsurutani, 15 Aug 2025
-
RC1: 'Comment on egusphere-2025-2857', Anonymous Referee #1, 28 Jul 2025
Review comments on the manuscript egusphere-2025-2857 entitled "A comparison of methods to compute the rate of horizontal geomagnetic field variation" by Fielding et al.
This study deal with possible indicators for geomagnetically induced currents (GIC). The authors have presented a comparison between two approaches that determine change rates of local magnetic variations. Several authors have used the temporal changes of the horizontal field component, H', as an indicator for GIC activity. Others have used the modulus of the change rates from the two horizontal components, R, as the indicator. As expected, R is always larger than H', and this difference depends on the local declination angle. The statistical characteristics of the R/H' ratio are investigated and also its dependence on the resolution of the recordings.
While the presented results clearly show the advantage of R over H' time series, the study is limited to technical descriptions. It provides next to no scientific interpretation. I could imagine that such reports are more suitable for other journals. Readers of Annales Geophysicae expect more scientifically relevant articles.
Further comments are detailed below.
General comments
- Relevant GICs are caused by rapid and large changes of the geomagnetic field. Since this is the focus of the study, it is not very helpful to look at the statistical properties of field variations at a certain station. Your extended elaboration of the situation near 0° Declination and the discussion of magnetometer resolution makes not much sense in the context of GICs. Of relevance are the few percent of largest changes. From the nice and large dataset, I could think of taking just the 1% largest cases at the various stations. Determining from them the R to H' properties, e.g. latitude dependence, local time variation, etc. would make more sense.
- Your study implies that the R to H' ratio is mainly a determined by the declination angle. If that is correct, R and H' do an equally good job because the declination is rather constant. The conversion to GIC would require just a different scaling factor. However, it is expected that the focusing on the large cases will provide different answers, depending on the latitude range and other factors. Here more scientific aspects could be considered in the study. What are the main current types that cause the severe changes at the latitude ranges? Are these electrojets, affecting mainly the north component, or the travelling westward surge at substorm onset, which are clearer in the east component, effects of SSC and ring current changes, best seen in H component. Such an investigation would give the user a scientifically justified recommendation at hand.
Special comments
Line 56: Delete "there are"
Line 60ff: It is not clear how you derived the differences shown in Figure 1. H' is varying between positive and negative values, R is positive definite. In the case of a sine wave H' has the same deflections in positive and negative direction. R from Eq. (3) has only positive values, it comes at twice the frequency, and the peak-to-peak differences are half as large. Please describe in detail how you arrived at the values shown in Figure 1 and the following figures.
Line 227: Delete "for each"
Citation: https://doi.org/10.5194/egusphere-2025-2857-RC1
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 988 | 33 | 17 | 1,038 | 61 | 68 |
- HTML: 988
- PDF: 33
- XML: 17
- Total: 1,038
- BibTeX: 61
- EndNote: 68
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1