the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2025
Spatiotemporal Recurrence Pattern of Earth’s Polar Cap Variation During Geomagnetic Storms
Abstract. This study examined the recurrence patterns of Earth's polar cap activities in response to various geomagnetic storm intensities. Time series data of polar cap indices (PCN and PCS) for great storm, severe storm, strong storm, moderate storm, and weak storm events were analysed. Nonlinear dynamics tools, including Recurrence Plot (RP), Recurrence Rate (RR), and Length of Diagonal Line (L), were applied to the polar cap variations to identify the recurring patterns associated with the various categories of geomagnetic storms. The RP, RR, and L effectively captured the distinct recurrence features in the PCN and PCS variations across different storm categories. During great storms, severe storms, and strong geomagnetic storms, the RPs unveils a strong deterministic structure for both PCN and PCS variations, whereas moderate and weak storms showed a rare deterministic structure of RP. Similarly, RR and L values were high during great storms, severe storms, and strong storms, however these indicators significantly decline during moderate and weak storms. These findings indicates that the recurrence density and deterministic behaviour in the polar cap activities, intensify with increased solar wind energy input into the magnetosphere.
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RC1: 'Comment on egusphere-2025-2810', Anonymous Referee #1, 02 Aug 2025
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This study (entitled “Spatiotemporal Recurrence Pattern of Earth’s Polar Cap Variation During Geomagnetic Storms” by Oludehinwa et al.) examine the recurrence patterns of the polar cap indices for the Northern and Southern Hemispheres (PCN and PCS, respectively) during geomagnetic storm events and their changes in response to the intensity of the geomagnetic storms. For this study, geomagnetic storms are categorized into five intensity groups (great storms, severe storms, strong storms, moderate storms, and weak storms) according to the minimum value in the SYM-H index during the interval of the corresponding geomagnetic storm events. For each of these five intensity groups, two geomagnetic storm events are selected to use Recurrence Plot (RP) and Recurrence Quantification Analysis (RQA) techniques. Based on the results in the RP for a total of 10 geomagnetic storm events in five intensity groups, as well as the results in the Recurrence Rate (RR) and average line length of the diagonal (L) obtained from the RQA for these events, the authors suggest that the recurrence density and deterministic behavior in the polar cap activities (which could be in terms of the ionospheric electric fields in the near-pole regions generated by the solar wind-magnetosphere interaction and therefore the transpolar ionospheric Hall currents related to these fields) intensify with increasing solar wind energy input into the magnetosphere.
Although the research topic in this study and the mathematical methods used here for data analysis are somewhat interesting, it is needed to address incomplete information and difficult-to-understand data selection methods for the analysis, as well as the typos and grammatical errors. Therefore, this reviewer suggests that this manuscript requires substantial changes before it can be reconsidered for publication. The relevant comments are provided below.
MAJOR COMMENTS
- Identification method of geomagnetic storm events: The authors select two geomagnetic storm events for each of five categories divided based on the minimum value in the SYM-H index. Then,
- It is unclear if there are any reasons that the authors examine ONLY TWO geomagnetic storm events for each of the five categories.
- This reviewer recommends providing the start time and end time of the geomagnetic storm events (rather than the storm occurrence date) and the time when the SYM-H index is minimum in Table 1.
- Recurrence plot analysis method
- Equation 1 (xi = (x1, x2, …, xn), i = 1, 2, …, 1440) #1: Because this study focuses on the recurrence pattern of the variations in the (1-min resolution) polar cap indices “during geomagnetic storms”, the numbers of the time series data (i) in both the PCN and PCS indices for geomagnetic storm events can vary depending on the number of minutes in the time interval of the events. Therefore, all analyses used in this study could be performed using the polar cap indices during the geomagnetic storm intervals, instead of the storm occurrence dates. This reviewer cannot find any reasons that the numbers of data points in both polar cap indices are fixed to 1440 (equivalent to 1-day data). It is also worth noting that the X-axis range in Figure 1 (01:00-23:00 UT in this version, rather than 00:00-24:00 UT) as well as the X-axis range and Y-axis range in Figures 2-6 can vary according to the time interval of the events.
- Equation 1 #2: It is difficult to understand what “xi = (x1, x2, …, xn)” means. Equation 1 needs to be rewritten more clearly.
- Line 111: It is unclear which value is used as the threshold distance (ε).
- Lines 125-126: How do the authors determine 15 as the embedding dimension (m = 15) and 6 as the time delay (τ = 6)?
- Interpretation of recurrence plot
- Section 3 #1: The results shown in Figures 2-6 can be provided in terms of visible elements such as diagonal lines, vertical/horizontal lines, clustering of points, and so on.
- Section 3 #2: It is needed to elaborate on the locations in Figures 2-6 that the authors pointed out in the text (for example, “… it was seen that the polar cap signals exhibit some coherent structure in its underlying dynamics.” on Lines 147-148, “The RPs observation for these severe geomagnetic storms captured a wide distribution of recurrence points, with a high density of recurrence points observed in all the severe storms investigated.” on Lines 162-164, and so on).
- Section 4 (Discussion and Conclusion): Only the discussion of the results obtained from the recurrence plots and from the recurrence quantification analysis (in terms of RR and L) has been provided in Section 4. It is also needed to provide the conclusion of this study in this section.
MINOR COMMENTS
- Title: The abstract and main body of this manuscript lead to a question about why the authors put “Spatiotemporal” in the title.
- Line 28: In “… the polar cap undergoes significant variations …”, please elaborate on the kind of variations the polar cap undergoes significantly.
- Lines 31-32: In “One of the parameters that measures the activities of the Earth’s polar cap is the Northern and Southern Hemisphere Polar Cap indices (PCN and PCS).”, please elaborate on which activities of the Earth’s polar cap.
- Lines 38-39: Detailed description about “some coherent structures, which are complex multiscale and chaotic” is needed. Moreover, it is unclear what “They” indicates.
- Line 65: “… and 2024-2018 …” → “… and 2004-2018 …”
- Line 68: “… middle latitude (MLT) …” → “… magnetic local time (MLT) …”
- Line 76: Rewrite “Donner and co” in different form.
- Lines 90-91: “In section 3, we unveiled our results and observation in section 4, the discussion and conclusion in section 5.” should be rewritten based on the main body of the manuscript.
- Line 92: 2.0 → 2
- Lines 108, 131, & 135: According to the title in Section 2 (Data Acquisition and the Concept of Nonlinear Dynamics), this section could be organized into two subsections by “Data Acquisition” and “Concept of Nonlinear Dynamics”.
- Equation 3 & Line 124: What does “i” mean in “εi”, which has not appeared on Line 111?
- Line 124, Line 134, & Line 140: Are the total number of considered states (N) on Line 124, the number of points (N) on Line 134, and the maximum possible line length in the RP (N) on Line 140 identical? Please also provide the values of N.
- Lines 129-130: It is NOT necessary to mention “Laminarity (LAM)”, “Entropy (ENTR)”, “Determinism (DET)”, and “Trapping Time (TT)” unless these measures are used in this study. Please rephrase this sentence.
- Equation 5: i (in the parentheses) → l
- Line 139: How do the authors obtain the length of a diagonal line (l)?
- Line 141 #1: 3.0 → 3
- Line 141 #2: Please re-arrange the subsections in Section 3 based on the observations of the polar cap indices and the results obtained from the recurrence plot and recurrence quantification analysis techniques.
- Line 148: Detailed descriptions about “some coherent structure in its underlying dynamics” and “these inherit coherent structures” are needed.
- Line 188 & Line 203: magenta → red (or orange)?
- Line 189 & Line 204: grey → purple?
- Line 213: 4.0 → 4
- Lines 228-229: What does “similarity dynamics” mean?
- Lines 278-280: Delete repetition.
- Lines 308-312: Delete repetition.
Throughout the manuscript,
- As mentioned in the first and second minor comments, please specify what kind of “polar cap activities”, “polar cap variation”, and so on the authors describe.
- Clear explanations about “deterministic structure” and “deterministic behavior” mentioned in this manuscript are also needed.
- Quanaaq → Qaanaaq
- The words “(EKL)”, “(PCN and PCS)”, “(PCN)”, “(PCS)”, “(RPs)”, “(RQA)”, “(L)”, and so on appear many times. Please find and correct the corresponding parts.
- The average line length of the diagonal (L) and length of the diagonal (l) could be distinguishable.
- The quality of this manuscript would be improved when the corrections of typos and grammar mistakes that have not been mentioned yet are made.
Citation: https://doi.org/10.5194/egusphere-2025-2810-RC1
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