We thank Dr. Jaynes for her highly positive assessment of our manuscript and for providing suggestions for improvement. In our response, we reproduce the Reviewer’s comments in italics and give our replies in roman type.

This publication details the collection and results of a citizen science effort to study the May 2024 superstorm. The results show compelling observations that are not possible through the traditional means due to the latitude extent of such a large geomagnetic disturbance. And the results also show detailed scientific characteristics of the storm, as exhibited by the particle energy content estimates as well as the reports of technological interruptions. Overall, this is an impressive overview of the May 2024 superstorm from the citizen science data collection perspective and offers tangible leads for further scientific research from a simple and elegantly-executed system of volunteer reporting.

The paper is in publishable form as it is. However, I have some suggestions (mostly that the authors could take or leave) so I submitted it as “accepted subject to minor revisions”. The suggestions are listed below.

Thank you so much for this extremely positive and encouraging introductory statement!

Line 26: I very much suggest naming this as the Gannon Storm for a couple reasons. (1) There will not ever be a consensus given by an authoritative source; the name that sticks is the one that most people use in the literature, so you are part of that decision-making here. (2) I think the Gannon Storm is the most appropriate name, both in the memory of Jenn but also in that the Mother’s Day name is not meaningful in much of the world that does not celebrate that holiday. Naming it for an impactful scientist is more genuine, I think. Also, there is a delegation to the US Space Weather Action Policy group that will recommend to name this storm for her officially (I think it happens later this month or next month). This is, of course, just suggestion and I’m not fiercely adamant about the change.

Thank you for providing those arguments in favour of choosing the Gannon Storm terminology. We appreciate these, and we will be happy to adopt this name in the revision of our paper (though we will keep the brief discussion on the “Mother’s Day Storm” alternative in the introduction).

Line 41: Might be worth mentioning the ‘CME that missed’ study from 2013. Baker, D. N., Li, X., Pulkkinen, A., Ngwira, C. M., Mays, M. L., Galvin, A. B., & Simunac, K. D. C. (2013). A major solar eruptive event in July 2012: Defining extreme space weather scenarios. Space Weather, 11(10), 585-591.

Thank you for suggesting this reference, we will refer to it in the revision of our manuscript.

Line 108: Are you only using Wind data? I think if you are using OMNI data products, you are using a combination of Wind, ACE and DSCOVR.

Thank you for pointing this out; we will correct our statement in the revision.

Line 118: Have you reached out to anyone to see if Artemis could provide solar wind data during the gap? They sometimes are in the right place and have reliable data to fill in the OMNI data. Not sure it matters enough to be worth the effort for this, though.

We haven’t, actually! We can try to look into it when preparing the revision, and if this proves conclusive within reasonable time scales, we can update the manuscript accordingly. It is good to know about this in any case, thank you for the suggestion!

Lines 127-145: While this detailed description of the storm characteristics and phases is worthwhile, I was left wondering how this compares to the rest of the solar cycle. It might be a nice addition to add some comparisons such as the last time Dst was below -400 nT or how often the SME reached similar or greater values throughout the previous decade. This should be fairly easy with the historical OMNI data. I think it would add a very nice context to all the numbers quoted in these paragraphs.

Great suggestion! We will look into this and add our findings to the revision.

Lines 203-204 and Figure 2: It is nearly impossible to distinguish the blue dots from the black dots so I didn’t even realize there were Skywarden reports from Canada, New Zealand, etc until reading these lines and I can’t pick them out even knowing they are there. Would it be possible to make them X’s or some other symbol and also maybe a different color to help differentiate?

Thank you for pointing this out, we will rework the figure markers and colours to make sure all the data appears clearly.

Figure 5: Is it possible to add horizontal grid lines for the major ticks? I was wanting to compare the exact number of different colors at different locations but the format makes it difficult to do so. It sort of looks like pink/magenta outpaces green at all latitudes(!) but it’s a bit hard to tell.

Good suggestion, we will add the grid lines in the revised version of the figure.

Figure 6 and Lines 320-325: I think it would be very valuable to show the histogram of SZA for the green reports. I suspect you’ll see the opposite distribution - most of the green reports occurring at the higher SZAs. It would be interesting to see the comparison. I don’t know if it’s better to overplot the data (maybe with open, unfilled bars?) or to make a new panel.

Thank you for the suggestion, we will try to find the best way to add the SZA distribution for green aurora reports in Fig. 6a and add the corresponding discussion to the text.

Dear Dr Love,

Thank you for your interest in our study of the Gannon storm and for your question concerning our dataset. Hopefully co-author Emma Bruus provided you with the information you were afters.

Regards,

Maxime Grandin and co-authors

We thank the Reviewer for their positive assessment of our manuscript and for providing suggestions for improvement. In our response, we reproduce the Reviewer’s comments in italics and give our replies in roman type.

Summary

This is an excellent manuscript that has gathered citizen science contributions for reports of the auroral witnesses and disruptions of the human-made infrastructure. These results are showing how useful citizen science approach could be. In this sense, the authors' manuscript is a welcome contribution to the scientific community. However, some of their discussions do not look so new. This is especially the case with Section 2, Section 4.1.3, and Section 5.4. The authors should remove these sections to minimize their overlap with the previous studies and clarify their own novelty for further consideration on their potential publication. The authors need to appropriately cite the existing studies and clarify whether their results support these studies or not.

Thank you for this encouraging overall statement. We will consider shortening these sections where appropriate and referring to the studies which have been published since the initial submission of our manuscript.

Major Comments

1. Section 2 gave me an impression of déjà-vu without much novelty, as such analyses have been already posted elsewhere (DOI: 10.4401/ag-9117; DOI: 10.48550/arXiv.2408.14799; DOI: 10.48550/arXiv.2407.07665; DOI: 10.5140/JASS.2024.41.3.171). This section does not bring something significant new against these previous studies. This section neither helps their overall discussions. Therefore, the authors should remove this section. If some of their information is essential, the authors should include their minimal summaries in the introduction rather than their main body.

We thank the Reviewer for pointing to these studies which also present and discuss the driving conditions which led to the 10 May 2024 geomagnetic storm. While we appreciate that the drivers are not the main focus of our study, we however believe that it is always important to provide the context in which observations are made, especially minding that our readership in Geoscience Communication is not necessarily from the space physics community.

Moreover, we wish to underline that two of the suggested references are currently available as preprints only, and a third one became available after we submitted our manuscript in July. The fourth reference is hence the only one which was available at the time when we wrote the manuscript, and it is already cited.

We will be happy to refer to those of the above studies which have been accepted by the time we can revise our manuscript. We will also consider shortening Section 2 to keep it to what is essential for the reader to get an overview of the context in which the geomagnetic storm took place.

2. The authors emphasize their data significance, based on the lack of midlatitude observations. However, in reality, the midlatitude auroral activity has been monitored with the Super Dual Auroral Radar Network (DOI: 10.1186/s40645-019-0270-5). The authors need to compare their results with the Super Dual Auroral Radar Network (DOI: 10.1186/s40645-019-0270-5), to substantiate their statement.

Thank you for mentioning the fact that SuperDARN radars provide observations of the mid-latitudes. However, we believe that our statement underlining the scarcity of midlatitude observations of the aurora still holds, for two main reasons. First, SuperDARN is a network of radars, and as such, it does not provide optical data that would enable inferring information on the aurora that we could directly compare with our data. The mid-latitude radar echoes are often in the subauroral region like SAPS. Auroral echoes can also be seen, but they are usually in the high-latitude portion of the field of view. Second, while part of the mid-latitudes are indeed covered by SuperDARN, many of the regions from which citizen scientists reported seeing the aurora are outside of the radar coverage: most of Australia, the north of New Zealand, almost all of Europe, the southern USA and Mexico, as well as the regions from which we received a few reports (South America, Namibia, China, India).

When revising the paper, we can add a statement mentioning SuperDARN and referring to the suggested article.

3. Their statement on the auroral oval expansion (P11-12) contradicts what DOI: 10.4401/ag-9117 stated. This article concludes that the actual auroral oval was not that wide (only down to 45-50 degree) and what was witnessed in the lower latitude should have been SAR arcs. The authors need to revise their statement based on DOI: 10.4401/ag-9117 or show enough evidence to overturn what DOI: 10.4401/ag-9117 stated.

What Spogli et al. (2024) state is that “It appears highly improbable that auroras could have been visible as far South as Italy or even Africa.” Their statement is based on the fact that the OVATION Prime model output did not produce an extension of the auroral oval to such low latitudes. The authors suggest that the reports from those regions might actually be SAR arc observations, but their phrasing remains careful on the matter. In fact, looking at the picture taken from Stintino (Italy) by Fabrizio Perra and shown in their Fig. 11, there is very clear evidence of field-aligned structuring in the optical emission, hinting at aurora rather than SAR arcs which are generally diffuse. This is also consistent with the report of “red and violet glows” in their paper: SAR arcs are monochromatic (red emission). Besides, we can note that the Spogli et al. (2024) study focuses on the European-sector observations, whereas our work also considers observations from North America which was near midnight at the peak of the storm main phase.

We therefore do not think that our statement on the auroral oval extent during the geomagnetic storm, based on our data, needs to be revised.

4. Their Section 4.1.3 and Figure 5 are not new, as similar results have been already published elsewhere (e.g., Figure 18 of DOI: 10.48550/arXiv.2407.07665). The authors should either remove this section. Otherwise, the authors need to minimize their description (down to 30% of the current amount) and clarify whether their results support these precious studies or not to clarify their novelty.

The paper to which the Reviewer is referring (by Hayakawa et al.) is a preprint which was uploaded to arXiv only two days before we submitted our manuscript to Geoscience Communications. It is therefore incorrect to refer to this paper as “published”.

In any case, Fig. 18 of Hayakawa et al., while also focusing on reported colours of auroral emissions during the 10 May 2024 geomagnetic storm, was based on a different data set than ours (76 reports from a different online survey). Therefore, it will be very interesting to discuss the differences and similarities between their results and ours, but it would seem quite inappropriate to not show the auroral colour distribution in our paper and discuss it.

5. The satellite drags (Section 5.4) have been already discussed in detail in DOI: 10.2514/1.A36164. It is not immediately clear how their citizen science approach can benefit discussions on the satellite drags either. The authors need to remove Section 5.4. Otherwise, the authors need to minimize their description (down to 30% of the current amount) and clarify whether their results support these precious studies or not to clarify their novelty.

We agree that the discussion on storm effects on satellite drag is a bit deviating from the main focus of our study, and we will be happy to consider shortening this section in the revision of our manuscript (though not down to 30% of the initial amount). However, we think that the quantitative estimates of LEO satellite altitude loss imputable to the storm that we provide with Fig. 9 are new compared to the results presented in Parker and Linares (2024), which is already cited in our manuscript. While Parker and Linares (2024) carried out an extensive analysis on atmospheric density increase inferred from satellite drag and analysed the manoeuvers by satellite operators following their satellites’ altitude loss, we look at four individual LEO objects and quantify for each of them the altitude loss imputable to the storm. Our purpose here is to add to the discussion that publicly available data can also be used for doing science.

6. The authors should appropriately show what has been revealed in the previous studies for this storm and whether their results support the previous studies or deny their results. Even for the geophysical contexts, auroral activity, and satellite drags, we can easily raise the following studies (DOI: 10.4401/ag-9117; DOI: 10.48550/arXiv.2408.14799; DOI: 10.48550/arXiv.2407.07665; DOI: 10.5140/JASS.2024.41.3.171; DOI: 10.2514/1.A36164). There are many more. The authors should contextualise their manuscript to these previous studies.

As mentioned in our response to point 2., most of the studies the Reviewer refers to were not yet available at the time when we submitted our manuscript, and several of them are also at the stage of preprints – they hence cannot be qualified as “previous studies” compared to ours.

When revising our manuscript, we will update our introduction and discussion by including references to the newly accepted publications available at that time.

7. The manuscript is extremely long. This reduces the readability. The authors should compress the length of the manuscript to 50% to 60%. For this, the authors should remove their sections overlapping with the previous studies.

While we acknowledge the fact that this is a long manuscript (albeit significantly shorter than, for instance, the preprint by Hayakawa et al. with doi 10.48550/arXiv.2407.07665 referred to by the Reviewer), we do not understand the reasoning behind the need for reducing its length to 50% to 60%. These numbers seem a bit arbitrary, and it is unreasonable to remove entire sections on the basis that other studies, which were submitted after our manuscript or at the same time, address similar aspects. In any case, our data set and methods are largely different from those presented in the other studies the Reviewer has referred to, so we believe that there is room for everyone to contribute to the scientific discussion in a constructive rather than competitive way.

That said, we recognise the value of streamlining the text where possible and will make efforts to condense certain sections without compromising the integrity of the content when revising the paper.

8. It is not immediately clear what the authors have revealed in this study, in comparison with what has been already revealed in the Aurorasaurus Project. The authors' conclusions 1 and 2 look evident from the Aurorasaurus Project. The authors should clarify their own novelty against the Aurorasaurus Projects.

We can happily emphasise in more detail the importance of Aurorasaurus and can include a discussion of results on the 10 May 2024 storm as yielded by the Aurorasaurus project. We see this as a great addition and the reason it was not included was that, at the time when we submitted our manuscript, there were not yet any peer-reviewed publications nor preprints to refer to.

We will make sure to emphasise clearly the differences between our results and those coming from the Aurorasaurus project in the revision.

Minor Comments

P1 L4 The authors have stated that cameras are not from traditional scientific instruments. This is slightly different from the reality. Cameras have also been used for auroral observations for more than decades. The authors can easily reference several scientific achievements from the early auroral photographs even within recent highlights such as those in Sodankylä (DOI: 10.1007/978-3-642-31457-5; DOI: 10.5194/hgss-15-17-2024).

Thank you for underlining that our phrasing (“ Hence, many people not only witnessed but also photographed the aurora during this event. These observations, although not from traditional scientific instruments...”) may be considered ambiguous. We will rephrase this statement to make it clear to the reader that we are referring to citizen science observations as opposed to observations by instruments maintained and operated by researchers or engineers for the sake of doing science.

P1 L11 The authors have considered their main finding as "the aurora was widely seen from locations at geomagnetic latitudes ranging between 30◦ and 60◦, with a few reports from even lower latitudes". However, similar finding has been already reported in multiple articles (DOI: 10.4401/ag-9117; DOI: 10.48550/arXiv.2407.07665).

This comment seems to partly contradict the Reviewer’s major comment #3 underlining that Spogli et al. (2024) suggested that the auroral oval might not have reached latitudes as low as Italy or the southern tip of Africa. And as explained in earlier replies, Hayakawa et al. is still at the stage of preprint. We will be happy to compare and discuss results with other recent studies as available at the time when we resubmit our paper.

P2 L20 The aurorae were seen even before Babylonians. (DOI: 10.1007/s11214-023-01018-1). This statement needs to be corrected.

Thank you for pointing to this very interesting paper! We will amend our statement accordingly.

P2 L23 It might be worth citing statistical studies to support this statement here (DOI:10.1029/2020JA028284).

Thank you, we can indeed add a citation to this paper in the revision, as it directly supports our statement.

P2 L25 The latest storm before this took place in November 2003 rather than in the Halloween of 2003 (DOI: 10.1029/2018JA026425).

Indeed, we will explicitly mention that the strongest storm of the 2003 events took place in November – although the set of events is often referred to as “2003 Halloween storms” in the literature.

P2 L28 For this storm, the source active regions and coronal mass ejections have been already documented in the previous studies (DOI: 10.4401/ag-9117; DOI: 10.48550/arXiv.2407.07665). They needed to be mentioned here.

We can of course also include a reference to Spogli et al. (2024) already on this line, indeed.

P2 L32 Some articles have been published for the space-weather impact of this events such as the satellite drags (DOI: 10.2514/1.A36164).

The statement on P2 L32 is a general statement, not specific to the 10 May 2024 event. The references we have already cited in this paragraph are therefore more relevant than Parker and Linares (2024), which we cite later in the manuscript.

P2 L41 Their statements on the Carrington storm is somewhat outdated. A lot have been studied for the Carrington event in the last two decades after Siscoe et al. (2006).

Siscoe et al. (2006) is the study which estimated the Dst index associated with the Carrington storm, so it feels like a very appropriate reference to back up the statement that “the September 1859 “Carrington” event is one of the largest storms ever documented for which geomagnetic indices have been estimated.”

P3 L51 The Kp index for this storm has been better defined in the recent studies along with the Hpo indices (DOI: 10.22541/essoar.171838396.68563140/v2).

Thank you for pointing to this preprint. We can consider whether to refer to its results when revising our manuscript.

P3 L53 the authors need to cite representative references for the AI-based forecasts of the geomagnetic conditions of the superstorms.

Thank you for pointing this out. We will find a reference to justify the statement that AI tools are not performing well when being presented with inputs that are not representative of the conditions present in their training data set.

P6 L150 supplementing optical observations from scientific instruments which are relatively sparse at mid-latitudes => supplementing optical observations from scientific instruments which mainly concentrate in the polar regions

Thank you for this suggestion, we can adopt it in the revised paper.

P6 L150 We need to think twice about this statement. Midlatitude auroral activity has been efficiently monitored with networks such as the Super Dual Auroral Radar Network (DOI: 10.1186/s40645-019-0270-5). The authors should appreciate such networks too.

We certainly appreciate the SuperDARN network! However, the statement is here quite unambiguously referring to optical instruments: “supplementing optical observations from scientific instruments which are relatively sparse at mid-latitudes.”

P7 L154 Similar online survey has been taken in the previous studies too (DOI: 10.48550/arXiv.2407.07665). Such existing attempts should be mentioned.

As pointed out in earlier replies, Hayakawa et al. is a preprint which (to our current knowledge) has not been accepted for publication yet. We can however mention it in the revision, hoping that by the time of publication of our paper it will have a final-version DOI.

P8 L189 Can the authors clearly state that almost all the contributors reported their timestamps in their local standard time? I would not be surprised even if some of them have reported their timestamps in the Universal Time

We can add such a statement, as only a handful of the contributors reported their observations in UTC.

P9 L200 A total of 688 citizen scientists (out of the 696 respondents) indicated that they saw the aurora => A total of 688 citizen scientists (out of the 696 respondents) indicated that they photographed the aurora; If the authors mean that these citizen scientists managed to see the aurora by their own eye without instruments, the authors should maintain their original statement.

This number includes the reports from citizen scientists who saw and/or photographed the aurora; we will clarify this in the revision.

P9 L208-L217 The authors need to clarify that these issues have been pointed in the previous studies (DOI: 10.48550/arXiv.2407.07665).

Same as above: we will happily refer to Hayakawa et al. but cannot consider it a peer-reviewed publication at this point in time.

P9 L220 The authors need to cite these news pieces with appropriate references rather than just their URLs. For the auroral visibility in Korea and Japan, the authors should cite DOI: 10.5140/JASS.2024.41.3.171 and DOI: 10.48550/arXiv.2407.07665.

Thank you for providing us with the reference to the recently published Kwak et al. (2024) paper about observations of aurora in Korea. We will of course replace the news website URLs with peer-reviewed publications as much as possible when revising our manuscript.

P11 L253 The "sighting" should be replaced to "photographing" or "imaging", unless otherwise this is a naked-eye observation.

We will replace it with “observation”, which encompasses both naked-eye and imaging.