Effects of the Geomagnetic Superstorms of 10–11 May 2024 and 7–11 October 2024 on the Ionosphere and Plasmasphere

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This  manuscript  discusses the strongest geomagnetic storms of the solar cycle 25 happened due to arrival of the solar coronal mass ejection on May 10, 2024 and on October 10, 2024.

It analyzes characteristics of the solar wind, geomagnetic indices, as well as results of the vertical total electron content (VTEC), ionosonde and plasmaspheric observations at different longitude and latitude sectors in Europe, North Africa, Korea and USA. It allowed comparing the storms effects at different latitudes as well as the effect of the local time at the onset of the events. Significant depletion of the VTEC was observed that led to disappearance of the F2 layer in the ionosonde observations. The authors found, that although the both storms were of similar strength, the recovery phase to normal electron density values ​​took significantly different time intervals due to seasonal differences in background. Based on the analysis data from VTEC and the low-Earth orbiting SWARM satellites measurements, applying the Belgian SWIFF Plasmasphere Model the authors conclude that the VTEC depletion is not only due to a decrease of the ionization in the F 2  layer, but also to a closer plasmapause.

The results will significantly contribute to future understanding of the causes of density changes in the ionosphere and plasmasphere associated with intense magnetic storms. There are no major issues with the manuscript, so it is acceptable for publication after minor revisions.

1.      Upon a formal review of the manuscript, the reviewer discovered that 16 out of the 30 references cited are self-citations. However, on opinion the reviewer, all the citations support the presented material and this does not diminish the value of this study.

2.      The right panel of Figure 4 could be improved in terms of quality.

3.      A more detailed explanation of how the VTEC data were obtained at the points marked with black dots in Figures 5 and 12 would be helpful for a reader.

 

Author Response

Comment 1: [This  manuscript  discusses the strongest geomagnetic storms of the solar cycle 25 happened due to arrival of the solar coronal mass ejection on May 10, 2024 and on October 10, 2024.

It analyzes characteristics of the solar wind, geomagnetic indices, as well as results of the vertical total electron content (VTEC), ionosonde and plasmaspheric observations at different longitude and latitude sectors in Europe, North Africa, Korea and USA. It allowed comparing the storms effects at different latitudes as well as the effect of the local time at the onset of the events. Significant depletion of the VTEC was observed that led to disappearance of the F2 layer in the ionosonde observations. The authors found, that although the both storms were of similar strength, the recovery phase to normal electron density values ​​took significantly different time intervals due to seasonal differences in background. Based on the analysis data from VTEC and the low-Earth orbiting SWARM satellites measurements, applying the Belgian SWIFF Plasmasphere Model the authors conclude that the VTEC depletion is not only due to a decrease of the ionization in the F 2  layer, but also to a closer plasmapause.

The results will significantly contribute to future understanding of the causes of density changes in the ionosphere and plasmasphere associated with intense magnetic storms. There are no major issues with the manuscript, so it is acceptable for publication after minor revisions.]

Response 1: [Thank you for your in-depth reading and your comments that helped us to improve the paper. Our changes in the article are in red.]

Comment 2: [1. Upon a formal review of the manuscript, the reviewer discovered that 16 out of the 30 references cited are self-citations. However, on opinion the reviewer, all the citations support the presented material and this does not diminish the value of this study.]

Response 2: [Because a lot of papers were published on the Mother’s Day event after our submission, several references have been added on this topic with a short summary in the introduction of what they brought as new results.]

Comment 3: [2. The right panel of Figure 4 could be improved in terms of quality.]

Response 3: [Figure 4 right panel is now given with better quality.]

Comment 4: [3. A more detailed explanation of how the VTEC data were obtained at the points marked with black dots in Figures 5 and 12 would be helpful for a reader.

Response 4: [This has been added in section 2.2. The dots represent the VTEC data used for the interpolation.]

Reviewer 2 Report

Comments and Suggestions for Authors

 

1. There are dozens of works devoted to the storm of May 10-11, 2024. Authors should briefly describe in the Introduction what was done BEFORE their work.

2. It is necessary to clearly formulate the list of unsolved problems.

3. The discussion should indicate how their results relate to the results obtained by other authors in previous works on this topic.

Author Response

Comment 1: [There are dozens of works devoted to the storm of May 10-11, 2024. Authors should briefly describe in the Introduction what was done BEFORE their work.

Response 1: [We thank the reviewer for taking the time to review this manuscript. Please find the detailed responses below. Our changes in the article are in red.

Because a lot of papers were indeed published on the Mother’s Day event after our submission, several references have been added on this topic with a short summary in the introduction of what they brought as new results.]

Comment 2: [It is necessary to clearly formulate the list of unsolved problems.]

Response 2: [A list of unsolved problems has been added in the introduction.]

Comment 3: [The discussion should indicate how their results relate to the results obtained by other authors in previous works on this topic.]

Response 3: [A discussion with previous publication references has been added in section 5.]

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents a well-structured analysis of the ionospheric and plasmaspheric responses to the May and October 2024 geomagnetic storms, incorporating diverse datasets effectively. However, refining the clarity of key findings, strengthening methodological justifications, and addressing inconsistencies in event descriptions would enhance its scientific impact. A more explicit discussion on novelty and model limitations is recommended. I have placed my comments below:

The manuscript primarily presents observational data and model comparisons, but it lacks a clear emphasis on novel insights. It would be beneficial to articulate how this study significantly advances the understanding of geomagnetic superstorms beyond prior works (e.g., Gallagher et al., 2021; Klimenko et al., 2015). Kindly Provide a stronger discussion on how this work differs from previous research.

Line 12-13: “On 10 May 2024 at 17h:07 UTC, the arrival of solar a coronal mass ejection (CME) generated the strongest geomagnetic storm of the last twenty years with a minimum Dst = -412 nT.”

The phrase “solar a coronal mass ejection” seems to have a typographical error. The claim of being the strongest in twenty years should be justified with historical references or a comparative table.

Line 14-15 vs. Line 364-369: The strength of the 10 October event (Dst=-335 nT) seems relatively smaller compared to the May event (Dst=-412 nT), yet the October storm's impact on ionization appears exaggerated in some sections. The October event's description should be more proportional to its actual geomagnetic intensity.

Line 50-51: “We use OMNI to obtain the solar wind parameters measured at 1 AU.” Clarify whether these OMNI data are from in-situ spacecraft or modeled values.

Line 55-64: Description of VTEC calculations lacks sufficient methodological rigor. Was any particular interpolation method used for estimating VTEC maps? Uncertainty quantification is not provided.

Figure 8 & 15: The description of plasma erosion is valuable, but it lacks direct observational validation. Adding satellite-derived plasmaspheric density measurements (e.g., SWARM data) would improve the discussion.

Author Response

Comments 1: [The manuscript presents a well-structured analysis of the ionospheric and plasmaspheric responses to the May and October 2024 geomagnetic storms, incorporating diverse datasets effectively. However, refining the clarity of key findings, strengthening methodological justifications, and addressing inconsistencies in event descriptions would enhance its scientific impact.]

Response 1: [Thank you for your in-depth reading and your comments that helped us to improve the paper. Our changes in the article are in red.]

Comments 2: [A more explicit discussion on novelty and model limitations is recommended. I have placed my comments below:

The manuscript primarily presents observational data and model comparisons, but it lacks a clear emphasis on novel insights. It would be beneficial to articulate how this study significantly advances the understanding of geomagnetic superstorms beyond prior works (e.g., Gallagher et al., 2021; Klimenko et al., 2015). Kindly Provide a stronger discussion on how this work differs from previous research.]

Response 2: [A more detailed introduction has been added about the Mother’s Day event and the previous results published about this event. This allows us to emphasize the unsolved problems for which a list has been added in the introduction. We explain how our study differs from previous research and shows how our approach is innovative. Instead of considering only one limited place, we give observations from Europe (quite rare in the previous publications), America ad Asia. The study is also based on the ionosphere-plasmasphere combination, on different kinds of instruments (ionosondes and GNSS) and on comparison of the 2 strongest events of the last 20 years.

A discussion has also been added before the conclusions to emphasize the new insights.]

Comments 3: [Line 12-13: “On 10 May 2024 at 17h:07 UTC, the arrival of solar a coronal mass ejection (CME) generated the strongest geomagnetic storm of the last twenty years with a minimum Dst = -412 nT.”

The phrase “solar a coronal mass ejection” seems to have a typographical error.

The claim of being the strongest in twenty years should be justified with historical references or a comparative table.]

Response 3: [The typo has been corrected. We added references and a bottom panel in Figure 3 showing Dst from 2000 to 2025.]

Comments 4: [Line 14-15 vs. Line 364-369: The strength of the 10 October event (Dst=-335 nT) seems relatively smaller compared to the May event (Dst=-412 nT), yet the October storm's impact on ionization appears exaggerated in some sections. The October event's description should be more proportional to its actual geomagnetic intensity.]

Response 4: [We have added a bottom panel in Figure 3 to clearly illustrate that the intensity of the October geomagnetic storm is also very strong (the strongest after Mother’s Day since November 2004).]

Comments 5: [Line 50-51: “We use OMNI to obtain the solar wind parameters measured at 1 AU.” Clarify whether these OMNI data are from in-situ spacecraft or modeled values.]

Response 5: [OMNI are from in situ spacecraft. This has been added.]

Comments 6: [Line 55-64: Description of VTEC calculations lacks sufficient methodological rigor. Was any particular interpolation method used for estimating VTEC maps? Uncertainty quantification is not provided.]

Response 6: [A new paragraph has been added in section 2.2 to better explain how VTEC is calculated.]

Comments 7: [Figure 8 & 15: The description of plasma erosion is valuable, but it lacks direct observational validation. Adding satellite-derived plasmaspheric density measurements (e.g., SWARM data) would improve the discussion.]

Response 7: [A new article (Paul et al., 2025) published just during this review process in February 2025 has analysed SWARM data of the Mother’s Day event. We have added this reference and its results (an equatorward displacement of the Midlatitude Ionospheric Trough) in the final discussion of the paper.]

Reviewer 4 Report

Comments and Suggestions for Authors

Comments to the manuscript atmosphere 3466599

Effects of the geomagnetic superstorms of 10-11 May 2024 and 7-11 October 2024 on the ionosphere and plasmasphere

by Pierrard V., T. Verhulst, J.-M. Chevalier, N. Bergeot and A. Winant

 

The May 2024 event was to some extent both expected and unexpected and aroused great interest and a flow of publications. The difference of this work is the parallel study of two powerful events. Despite the differences in seasons and intensity of disturbances, common features were also discovered. Another difference is a detailed study of the role of the plasmaspheric part.The paper is very interesting and can be recommended for publication, as it meets all the criteria of the journal, but several simple situations need to be clarified. 

Comments

1.Line 74: probably Ne under the root is NmF2?2.Lines 92-93, Table 1: which station corresponds to location (a)?3. Line 127: There is no paper (Botek et al., 2021) in the list of publications.4. Lines 182-183: what does the expected VTEC mean? Mean, median?5. Lines 351-352, Figure 9: What do the dots mean?

 

Comments for author File: Comments.pdf

Author Response

Comments 1: [The May 2024 event was to some extent both expected and unexpected and aroused great interest and a flow of publications. The difference of this work is the parallel study of two powerful events. Despite the differences in seasons and intensity of disturbances, common features were also discovered. Another difference is a detailed study of the role of the plasmaspheric part. The paper is very interesting and can be recommended for publication, as it meets all the criteria of the journal, but several simple situations need to be clarified. ]

Response 1: [Thanks for your reading and your comments that help us to improve the paper. Our changes in the article are in red.]

Comments 2: [1.Line 74: probably Ne under the root is NmF2?]

Response 2: [No, the formula for the plasma frequency is valid at all points in the electron distribution, not only at the peak. If one puts the peak density NmF2 as the density Ne, then omega = foF2. Precisely because the formula is valid everywhere, it allows use to reconstruct the entire electron density, not only the peak.]

Comments 3: [2.Lines 92-93, Table 1: which station corresponds to location (a)?]

Response 3: [We think the reviewer means location a) of Figure 4. The map in Figure 4 shows the location of the data extracted from the ionospheric TEC maps, while Table 1 shows the places of ionosondes. Ionosonde DB049 is close to location b), but no ionosondes are exactly collocated with any of the the locations (a) and (c) of the GNSS-based TEC. For easier localisation of ionosondes in Table 1, we added the country where the stations are located.]

Comments 4: [3. Line 127: There is no paper (Botek et al., 2021) in the list of publications.]

Response 4: [Thanks. Added.]

Comments 5: [4. Lines 182-183: what does the expected VTEC mean? Mean, median?]

Response 5: [Median has been added L252 (section 3.2) and a new paragraph has been added in section 2.2 to better explain how VTEC is calculated.]

Comments 6: [5. Lines 351-352, Figure 9: What do the dots mean? ]

Response 6: [The dots show the plasmapause index, based on the L-value distance between the small-scale Field Aligned Current boundary and the mid-latitude ionospheric trough minimum. This has been added in the text.]

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have refined the manuscript based on my comments. I do not have any further queries.