<p>This study investigates the ionospheric saturation effect in the total electron content (TEC) response to solar activity using long-term global ionospheric map data spanning 1999–2024. Empirical mode decomposition is used to isolate long-term solar-cycle variability, and a two-segment regression model provides a consistent diagnostic of the saturation threshold in TEC versus solar proxy F10.7p. The global distribution exhibits pronounced local-time and seasonal patterns, with strong occurrence at low latitudes during equinoxes and enhanced mid- and high-latitude occurrence in the summer hemispheres during solstice seasons. Although saturation is most pronounced within localized high-density structures such as the Equatorial Ionosphere Anomaly, Weddell Sea Anomaly, and Yakutsk&#xa0;Anomaly regions, the broader hemispheric occurrence, particularly in the summer hemispheres, shows only weak correlations with TEC, suggesting that additional drivers such as neutral winds and composition changes must also be considered.</p>

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Global characteristics of the saturation effect in the TEC response to solar activity

  • Chun-Yen Huang,
  • Jann-Yenq Liu,
  • Tatsuhiro Yokoyama,
  • Peng Liu,
  • Chi-Yen Lin,
  • Fu-Yuan Chang,
  • Yuh-Ing Chen

摘要

This study investigates the ionospheric saturation effect in the total electron content (TEC) response to solar activity using long-term global ionospheric map data spanning 1999–2024. Empirical mode decomposition is used to isolate long-term solar-cycle variability, and a two-segment regression model provides a consistent diagnostic of the saturation threshold in TEC versus solar proxy F10.7p. The global distribution exhibits pronounced local-time and seasonal patterns, with strong occurrence at low latitudes during equinoxes and enhanced mid- and high-latitude occurrence in the summer hemispheres during solstice seasons. Although saturation is most pronounced within localized high-density structures such as the Equatorial Ionosphere Anomaly, Weddell Sea Anomaly, and Yakutsk Anomaly regions, the broader hemispheric occurrence, particularly in the summer hemispheres, shows only weak correlations with TEC, suggesting that additional drivers such as neutral winds and composition changes must also be considered.