the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 30 Jan 2025
Ionospheric Plasma Irregularities During Intense geomagnetic storms of Solar Cycle 25
Abstract. This study aims to characterize several key aspects of the ionosphere during intense geomagnetic storms that occurred on March 23–25, 2023, April 23–25, 2023, November 4–7, 2023 and May 10–13, 2024 during the ascending phase of Solar Cycle 25 (SC25). We are especially interested to study the role of asymmetric Joule Heating (JH) in the structuring of the Equatorial Ionization Anomaly (EIA), such as double crest, single crest, or merged, which may lead to the formation or suppression of post-sunset ionospheric plasma irregularities. For this purpose, we use the Weimer 2005 Model simulations to analyze the JH patterns during the four strong geomagnetic storms, and Madrigal TEC maps are used to observe changes in the intensity, location, and symmetry of the EIA during these disruptive times. Equatorial/low-latitude ionospheric plasma irregularities at different longitudes under geomagnetically disturbed conditions are studied using the Rate of Change TEC Index (ROTI), which is calculated from GPS receiver measurements. A strong JH is observed during the May 2024 storm (also known as the Mother's Day storm) during its main phase, which occurs after sunset between 18:00 and 00:00 UT. The other storms have the JH strength in the following order from strong to weak: March 2023, April 2023, and November 2023. Besides inter-hemispheric asymmetry, all the storms show stronger variation in the JH patterns. We conclude that the resulting change in the thermospheric winds and electric fields due to storm conditions alter the EIA structures. It has been found that the generation of ionospheric plasma irregularities and their geographical distribution strongly depend on EIA's density gradients and general structure. For instance, it is noticed that the double crest EIA structures with strong plasma density gradients play important role to the generation of post sunset ionospheric plasma irregularities during the main phases of these geomagnetic storms. On the other hand, the single crest or merged EIA structure comprise of a diffuse region of high electron density centered directly over the equator, without a pronounced trough, as observed during the storm of November 2023. The single crest EIA exhibit nearly uniform plasma density distribution do not favor the generation of ionospheric plasma irregularities. The role of storm-time penetrating electric field in the structuring and seeding of ionospheric plasma irregularities has been investigated. The research will contribute to our understanding of the basic physics of the ionosphere, especially the mechanisms governing the development and evolution of the EIA and ionospheric plasma irregularities under various magnetically disturbed conditions.
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RC1: 'Comment on egusphere-2025-86', Ephrem Seba, 18 Mar 2025
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Review: Nadia et al “Ionospheric Plasma Irregularities During Intense geomagnetic storms of Solar Cycle 25”
General comments:
This study investigates the characteristics of ionospheric plasma irregularities during intense geomagnetic storms in Solar Cycle 25, focusing on the role of Joule Heating (JH) and the Equatorial Ionization Anomaly (EIA). Using the Weimer 2005 model, Madrigal TEC maps, and ROTI (Rate of TEC Index) derived from GPS data, the authors analyze four major storms (March 2023, April 2023, November 2023, and May 2024). The findings reveal that JH exhibits significant interhemispheric asymmetries, with stronger heating in the northern hemisphere during some storms and the southern hemisphere during others. According to the paper, these asymmetries, along with storm-time electric fields and neutral winds, influence the formation of EIA structures (double crest, single crest, or merged) and the generation of post-sunset ionospheric irregularities. The document is a well written and structured document in general.
However, although the authors have made a commendable effort to investigate various aspects of geomagnetic storms and their connections to ionospheric plasma irregularities and the Equatorial Ionization Anomaly (EIA), it is surprising that they did not adequately highlight their important findings in the conclusion section, despite discussing them in detail in the Results and Discussion section. The current Conclusion is brief and fails to fully capture the depth and significance of the findings presented earlier. Also the paper lacks some physical explanations on causality relationships related to joule heating, suppressing of plasma irregularities and also lacks addressing the importance of local time in analyzing storm impacts on irregularities and EIA. Below, I outline major issues that the authors should address to strengthen the manuscript and enhance its scientific impact.Major comments
The authors present ROTI plots in Universal Time (UT), which makes it difficult to interpret the local time dependence of irregularities. Since ionospheric phenomena like post-sunset irregularities are strongly influenced by local time, this choice limits the interpretability of the results. Local time (LT) plots would better visualize the storm-time impact and allow comparisons across different longitude sectors. Therefore, the authors should replot their ROTI in Local Time (LT), even though they provided LT information in table 1, to better capture the local time dependence of irregularities. This would allow them to identify whether irregularities are enhanced or suppressed during specific local times (e.g., post-sunset, post-midnight) and also correlate storm impacts with the local time of SSC and main phase onset. The authors also mention plasma irregularity suppression during certain geomagnetic storms (e.g., November 2023), this would be good in terms of local time discussions. Several studies identified the importance of the local time at which geomagnetic storms happen to explain their impact on the ionosphere. Please review these documents to gain a better understanding of the above, including discussions related to DDEF, PPEF, and the suppression of irregularities.
• Liu, J., Zhao, B., & Liu, L. (2010, March). Time delay and duration of ionospheric total electron content responses to geomagnetic disturbances. In Annales Geophysicae (Vol. 28, No. 3, pp. 795-805). Copernicus GmbH.
• Amaechi, P. O., Oyeyemi, E. O., & Akala, A. O. (2018). Geomagnetic storm effects on the occurrences of ionospheric irregularities over the African equatorial/low-latitude region. Advances in Space Research, 61(8), 2074-2090.
• Araujo-Pradere, E. A., Fuller-Rowell, T. J., Codrescu, M. V., & Bilitza, D. (2005). Characteristics of the ionospheric variability as a function of season, latitude, local time, and geomagnetic activity. Radio Science, 40(05), 1-15.
• Seba, E. B., & Nigussie, M. (2016). Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector. Advances in space Research, 58(9), 1708-1719.
The authors attempt to link high-latitude Joule Heating (JH) with the Equatorial Ionization Anomaly (EIA), which is a low-latitude phenomenon (lines 240-250). While this is an interesting approach, the connection between these two regions is not clearly explained in the paper. The paper shows correlations between JH and EIA structures, but it does not establish a causal relationship. The authors should provide more evidence or references to support their claim that JH directly influences EIA and explicitly state the mechanism by which high-latitude JH influences low-latitude EIA. Do the authors propose that JH-driven thermospheric winds transport plasma or alter neutral composition, thereby affecting EIA structures? The authors observe interhemispheric asymmetries in JH (e.g., stronger JH in the northern hemisphere during the May 2024 storm). How do these asymmetries translate to differences in EIA structures or irregularities at low latitudes?The authors' discussion on the relationship between EIA structures and ionospheric irregularities is a good starting point, but it lacks several critical elements that would make their findings more robust, insightful, and convincing. That is, the authors do not provide a detailed mechanistic explanation of how specific EIA structures (e.g., double crest, single crest, or merged) influence the formation or suppression of irregularities. For example: How do density gradients in the EIA directly affect the night time growth of Rayleigh-Taylor instabilities?
Please review the followings for further understanding:
• Luan, X. (2021). Equatorial ionization anomaly variations during geomagnetic storms. Ionosphere dynamics and applications, 301-312.
• Balan, N., Liu, L., & Le, H. (2018). A brief review of equatorial ionization anomaly and ionospheric irregularities. Earth and Planetary Physics, 2(4), 257-275.
• Seba, E. B., Nigussie, M., & Moldwin, M. B. (2018). The relationship between equatorial ionization anomaly and nighttime equatorial spread F in East Africa. Advances in Space Research, 62(7), 1737-1752.
• Aa, E., Chen, Y., & Luo, B. (2024). Dynamic expansion and merging of the equatorial ionization anomaly during the 10–11 May 2024 super geomagnetic storm. Remote Sensing, 16(22), 4290.Suggestion on the conclusion section
Here are my suggested potential findings that should be included in the conclusion section and summarized in the abstract, along with clear physical explanations (the physical explanations in discussion and conclusion).
Equatorial Ionization Anomaly (EIA) Structures:
The study identifies distinct EIA structures (double crest, single crest, and merged) during different phases of geomagnetic storms. For example: Double crest EIA structures with strong plasma density gradients are associated with the generation of post-sunset ionospheric irregularities. Single crest or merged EIA structures, observed during the November 2023 storm, are linked to weaker plasma density gradients and suppressed irregularities . The poleward expansion of EIA crests during intense storms (e.g., May 2024) is driven by enhanced eastward PPEFs and external fountain effects
Impact of Prompt Penetration Electric Fields (PPEFs):
The study highlights the critical role of PPEFs in shaping ionospheric irregularities. For instance: Eastward PPEFs during the May 2024 storm caused a super fountain effect, leading to significant TEC variations and poleward shifting of EIA crests. Westward PPEFs were observed to suppress post-sunset irregularities, as seen during the November 2023 storm. The polarity and duration of PPEFs vary across different longitudes, influencing the spatial distribution of irregularities.
Geographical and Temporal Variations in Ionospheric Irregularities:
The study demonstrates that the occurrence and intensity of ionospheric irregularities vary significantly with longitude, local time, and geomagnetic activity. For example: Post-sunset irregularities were most pronounced in the American sector during the March 2023 and May 2024 storms. Post-midnight irregularities were suppressed across all sectors during the November 2023 storm, likely due to weaker electric fields and lower ionospheric conductivity. The Rate of TEC Index (ROTI) analysis reveals that irregularities are strongly influenced by storm-time drivers, such as enhanced vertical plasma drifts and density gradients.
And also the followings: Interhemispheric Asymmetries in Thermospheric and Ionospheric Responses, Storm-Specific Ionospheric Responses, Implications for Space Weather ForecastingCitation: https://doi.org/10.5194/egusphere-2025-86-RC1
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