the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Aug 2025
Features Investigates of the geospace storm over China During May 10–12, 2024
Abstract. This study investigates the characteristics of geomagnetic and ionospheric disturbances over China associated with the intense geospace storm that occurred during May 10–12, 2024. Observations were conducted using data from nine Intermagnet observatories, four ionosondes, and multiple satellites from the GNSS. To examine the quasi-periodic temporal variations of magnetic field components, this study introduces systems spectral analysis exclusively. The analysis reveals that the geospace storm, classified as a severe event, was accompanied by both intense geomagnetic perturbations and significant negative ionospheric storms. During the geomagnetic storm, the peak-to-peak amplitude of variations in the X-, Y-, and Z-components reached 550–800 nT, 166–422 nT, and 100–412 nT, respectively. The duration of the geomagnetic storm was approximately 40–60 h. The fluctuation spectrum of the geomagnetic field predominantly featured components with periods of 200 min and 90 min. During the negative ionospheric storm, which lasted around 50 h, foF2 values decreased by 2–3 times, while electron density values decreased by 4–9 times. At the same time, hmF2 values increased by 200–300 km. Other ionogram parameters exhibited minor changes. Total electron content values during the storm decreased by 30–40 TECU during the day (by 2–3 times) and by 10 TECU at night (by 2 times). The causes leading to the negative ionospheric storm was primarily driven by the penetration of magnetospheric electric fields into the ionosphere, the enhancement of plasma convection, disturbances in the thermospheric chemical composition, the intensification of thermospheric winds, and plasma transport processes occurring in both vertical and horizontal directions.
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RC1: 'Comment on egusphere-2025-3661', Anonymous Referee #1, 18 Sep 2025
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AC1: 'Reply on RC1', tao xu, 29 Sep 2025
The authors are very grateful to the reviewer for kind criticism of the manuscript.
Lines 30–35 note that solar storms cause geospace storms on our planet. These storms manifest themselves in all geospheres and geophysical fields. Therefore, it is natural to consider magnetic storms and ionospheric storms separately. This does not mean that these storms do not interact. On the contrary, as can be seen from Figs. 4–12, it is during the magnetic storm that the greatest disturbances in ionospheric parameters occur, which are classified as negative ionospheric storms. It is the geophysical fields (magnetic and electric) that determine the dynamics of ionospheric storms. Disturbances in electron density lead to disruptions in the system of ionospheric currents, and therefore to changes in the levels of geomagnetic field components. Naturally, the interaction between magnetic and ionospheric storms does not end there. The coupling mechanisms naturally differ near the EIA and at mid-latitudes, as noted in the manuscript. For more details on the interaction, please see the paper of one of the co-authors (Chernogor L. F. What are a geospace storm and a pan-planetary storm? // Advances in Space Research. – 2025. https://doi.org/10.1016/j.asr.2025.08.016).
The authors are unsure what is meant by «template instructions» in Section 3.
The physical mechanisms of magnetic and ionospheric storms are well known. However, the authors commented briefly on them (lines 481–485, 501–505). A detailed description was not the purpose of the manuscript. The purpose of the work is specified: «This study presents the results of analyzing temporal variations in the geomagnetic field level... with the purpose of obtaining quantitative data on the parameters of magnetic and ionospheric storms, the dependence of these parameters on latitude within the Chinese region, and determining the periods of predominant oscillations in the level of the geomagnetic field».
Physical and mathematical simulation of the main processes under the influence of a geospace storm is the subject of a separate study.
Temporal variations are defined as any deviations of media parameters from the quiet (background) values that occurred on reference days or before the onset (after the end) of the storm. This terminology is generally accepted in geophysics.Citation: https://doi.org/10.5194/egusphere-2025-3661-AC1
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AC1: 'Reply on RC1', tao xu, 29 Sep 2025
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RC2: 'Comment on egusphere-2025-3661', Anonymous Referee #2, 19 Sep 2025
Referee report on “Features Investigates of the geospace storm over China During May 10–12, 2024” by Tao Xu et al., (MS No egusphere-2025-3661)
General comments
The manuscript describes ionospheric and geomagnetic disturbances recorded in the China region during the space weather storm in May 2025. A comprehensive list of publications analyzing the May 2025 storm is given in the reference list of the manuscript and briefly reviewed in its introductory part. With this manuscript the authors want to contribute to the common understanding of the strong storm case with their observations from a region which has not been addressed thoroughly in the previously published studies. Unfortunately, the discussion on how the China region observations match to the picture built in the previous publications remains very weak in current manuscript. Chinese observations are described in detail but their interpretation in terms of magnetosphere-ionosphere-thermosphere interactions is missing. Only a very general statement about the combined ionosphere-thermosphere effects which led to the negative ionospheric storm is given at the end of the manuscript.
Specific comments
The manuscript relies very much on the data analysis methods and indices introduced in the earlier papers by Chernogor. Although those papers are in principle accessible for the reader, it is difficult to interpret the indices and spectral analyses results in the context of this storm study. For example, the results of the three different modes of the systems spectra analysis (SSA) are presented, but the discussion on how the modes should be interpreted as individual results or as their combination is missing.
The ionospheric density observations based on ionosonde and GNSS data are partly coming from the same region as in the paper by Zhang R. et al (2024), while the magnetic field measurements in this manuscript would offer a new aspect in the storm analysis. Therefore, it is important to have a thorough discussion about physics (e.g. coupling with magnetospheric wave activity) behind the magnetometer data presented in the study.
Technical corrections & conclusion
The manuscript is written in a very cursory style, and the English language needs comprehensive checking. In terminology there are expressions which are either erroneous or non-typical in our field (e.g. expressions like particle speed, particle density, and particle temperature used in the description of solar wind properties which in the plot are fluid momentum parameters). Using professional language and terminology is one of the basic factors ensuring accuracy in scientific communication. Therefore, in my opinion, the manuscript in its current form is not ready for publication as a peer-reviewed scientific article.
Citation: https://doi.org/10.5194/egusphere-2025-3661-RC2 -
AC2: 'Reply on RC2', tao xu, 30 Sep 2025
Dear reviewer, the authors did not intend to supplement the «picture built in the previous publications». This picture is well described in the publications cited in the Introduction. For more information on the specifics of this storm and geospace storms in general, see, for example,
1. Chernogor L. F. Energetics of Physical Processes Operated on May 8–12, 2024: From the Solar Storm to Lithospheric Disturbances // Advances in Space Research. – 2025. – Vol. 75, Iss. 6. – Pp. 4825–4849. https://doi.org/10.1016/j.asr.2024.12.069
2. Chernogor L. F. What are a geospace storm and a pan-planetary storm? // Advances in Space Research. – 2025. https://doi.org/10.1016/j.asr.2025.08.016
The purpose of the study is the following: «This study presents the results of analyzing temporal variations in the geomagnetic field level... with the purpose of obtaining quantitative data on the parameters of magnetic and ionospheric storms, the dependence of these parameters on latitude within the Chinese region, and determining the periods of predominant oscillations in the level of the geomagnetic field».
As for a detailed physical interpretation of the storm processes in the China region, this will require physical and mathematical simulation. This may be the aim of a separate work. In this manuscript, we have only briefly described the main physical processes (lines 481–485, 501–505).
Regarding the «indices and spectral analyses results», the reviewer quite rightly notes that the authors «rely on the data analysis methods and indices introduced in the earlier papers by Chernogor», and these works are «in principle accessible for the reader». The indices were used for quantitative and qualitative assessment of storm intensities. The advantages and features of the SSA are briefly indicated in lines 375–381 (at the beginning of subsection 3.4). Here we will only add that the combined use of three integral transforms allows us to improve the frequency-time resolution and the assessment of the amplitudes of the components. A more detailed description of the indices or SSA would have significantly increased the already large volume of the manuscript, which the authors considered inappropriate.
Regarding the work by Zhang et al. (2024). Unlike these authors, we examined a large number of ionogram parameters that describe not only the F2 layer but also the F1 layer, as well as the lower ionosphere (parameter fmin). In addition, we noted a direct connection between the ionogram parameters and the magnetic storm (see Figs. 4–8 and their description). A more detailed description of the combined variations of the geomagnetic field and ionosphere, as already noted, would require detailed physical and mathematical simulation.
Regarding terminology: «particle density» was replaced by «solar wind plasma number density», «particle speed» was replaced by «solar wind speed», and «particle temperature» was replaced by «solar wind proton temperature».
The authors are very grateful to the reviewer for careful reading and detailed comments.Citation: https://doi.org/10.5194/egusphere-2025-3661-AC2
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AC2: 'Reply on RC2', tao xu, 30 Sep 2025
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Review of "Features Investigates of the geospace storm over China During May 10–12, 2024" by Xu et al.
The paper is concerned with local geomagnetic measurements over East Asia during the May 2024 superstorm. The authors provide an overview of the rapidly evolving literature surrounding the May 2024 superstorm and motivates their study by the relative scarcity of studies that substantiate the conditions over the East-Asian sector during this particular storm. The authors wish to fill in this perceived gap by providing time series analyses of various geomagnetic observations.
The manuscript is in need of a better narrative structure and flow. At present, the sections tend to read as a series of individual observations rather than a cohesive scientific argument. To improve clarity, this referee suggests ensuring each paragraph has a clear topic sentence that connects its findings to the paper's central claims. I also noted the inclusion of template instructions (e.g., in Section 3), which should be removed.
The referencing is limited, and the paper is not concerned with substantiating any physical mechanism, save for the very last paragraph of the paper (and the last sentence of the abstract); here, the authors refer to an established description of geospace during storms. This summary of the large-scale physics of the ionosphere-magnetosphere interaction is not directly connected to the specific observations of the authors.
The authors do not substantiate what is entailed by "temporal variation", a central quantity. Is this the standard deviation in a running window?
The manuscript's primary challenge is to clearly articulate its novel contribution to the existing literature. The introduction provides an excellent and thorough overview of recent publications on the May 2024 storm, but this also highlights that the East Asian sector has received considerable attention. To strengthen the paper, the authors should explicitly state what new physical insights or specific, unobserved details their analysis provides that are not present in the already-cited literature.
In its current form, the manuscript does not yet meet the threshold for publication in Annales Geophysicae due to the structural issues and the need to more clearly define its novel scientific contribution. However, this referee believes that a re-written manuscript, or a major revision of the present manuscript, could turn this work into a valuable contribution to the field.
Specifically, this entails refining the narrative, removing template artifacts, and framing the results in the context of what is already known to highlight the new insights that can be gleaned from the authors' dataset.