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<p>This study investigated the interplanetary drivers of 26 severe geomagnetic storms that occurred during Solar Cycle 23, spanning 1996 to 2006. The analysis focused on severe events with a peak Disturbance Storm Time (Dst) index value ≤ −150&#xa0;nT. Using data from the OMNI database, the study examines the relationships between storm intensity and various interplanetary and geomagnetic parameters. The results confirm that all 26 events were initiated by a prolonged southward component of the interplanetary magnetic field (IMF-B<sub>z</sub>), as measured by the GSM coordinate system, a condition crucial for facilitating magnetic reconnection and the subsequent transfer of energy to the Earth’s magnetosphere. While Dst is used to monitor the equatorial ring current intensity, Kp and ap are analyzed as indices reflecting global activity, noting that Kp is notably sensitive to solar wind dynamic pressure. Strong correlation coefficients are found between the peak Dst and the peak values of the total interplanetary magnetic field (IMF − B) (0.65) and its southward component (IMF − Bz) (0.67). The correlation with IMF-B is expected as high-field regions increase the probability of extreme −B<sub>z</sub>; however, we quantify this relationship to provide a baseline for comparison against solar proxies. It is emphasized that the fundamental physical driver is the convective electric field (E<sub>y</sub> = V × B<sub>z</sub>), which facilitates energy transfer. The highest correlations are observed with the geomagnetic indices Ap (0.70) and Kp (0.70). In contrast, solar proxies such as the sunspot number (SSN) and solar radio flux (F10.7) showed only weak correlations (0.26 and 0.32, respectively). A moderate correlation is observed between peak Dst and Solar wind velocity (V<sub>sw</sub>) (CC = 0.44). Analysis of the interplanetary structures revealed that simple magnetic clouds (sMC), sheath fields (SH), and combined sheath and magnetic cloud structures (SH + MC) collectively accounted for over 75% of these severe storms. The distribution of these drivers was highly dependent on the phase of the solar cycle, with sheath fields dominating at solar maximum and magnetic clouds prevailing during the rising and declining phases. This research shows that severe geomagnetic storm intensity is critically determined by specific interplanetary conditions (B, B<sub>z</sub>, and V<sub>sw</sub>), which have a much stronger influence than general solar activity proxies, SSN F (10.7), thus improving space weather forecasting accuracy.</p>

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An in-depth analysis of interplanetary drivers and their causal mechanisms for severe geomagnetic storms during the period from 1996 to 2006

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Swapnil Garg,
  • Omkar Prasad Tripathi,
  • Saket Kumar,
  • Palak Singh Thakur

摘要

This study investigated the interplanetary drivers of 26 severe geomagnetic storms that occurred during Solar Cycle 23, spanning 1996 to 2006. The analysis focused on severe events with a peak Disturbance Storm Time (Dst) index value ≤ −150 nT. Using data from the OMNI database, the study examines the relationships between storm intensity and various interplanetary and geomagnetic parameters. The results confirm that all 26 events were initiated by a prolonged southward component of the interplanetary magnetic field (IMF-Bz), as measured by the GSM coordinate system, a condition crucial for facilitating magnetic reconnection and the subsequent transfer of energy to the Earth’s magnetosphere. While Dst is used to monitor the equatorial ring current intensity, Kp and ap are analyzed as indices reflecting global activity, noting that Kp is notably sensitive to solar wind dynamic pressure. Strong correlation coefficients are found between the peak Dst and the peak values of the total interplanetary magnetic field (IMF − B) (0.65) and its southward component (IMF − Bz) (0.67). The correlation with IMF-B is expected as high-field regions increase the probability of extreme −Bz; however, we quantify this relationship to provide a baseline for comparison against solar proxies. It is emphasized that the fundamental physical driver is the convective electric field (Ey = V × Bz), which facilitates energy transfer. The highest correlations are observed with the geomagnetic indices Ap (0.70) and Kp (0.70). In contrast, solar proxies such as the sunspot number (SSN) and solar radio flux (F10.7) showed only weak correlations (0.26 and 0.32, respectively). A moderate correlation is observed between peak Dst and Solar wind velocity (Vsw) (CC = 0.44). Analysis of the interplanetary structures revealed that simple magnetic clouds (sMC), sheath fields (SH), and combined sheath and magnetic cloud structures (SH + MC) collectively accounted for over 75% of these severe storms. The distribution of these drivers was highly dependent on the phase of the solar cycle, with sheath fields dominating at solar maximum and magnetic clouds prevailing during the rising and declining phases. This research shows that severe geomagnetic storm intensity is critically determined by specific interplanetary conditions (B, Bz, and Vsw), which have a much stronger influence than general solar activity proxies, SSN F (10.7), thus improving space weather forecasting accuracy.