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<p>The central position of the South Atlantic Anomaly (SAA) has been drifting westward or northward, and the drift speeds exhibit a complex relationship with solar activity, which also affects the area of the SAA configuration. Using six years of data from the low-Earth orbit satellite CSES, we analyze the spatiotemporal evolution of the geomagnetic field and high-energy protons within the SAA during Solar Cycle 25. Low-energy protons (2.0–10.0 MeV) exhibit a characteristic double-peak structure, whereas high-energy protons (10.0–20.0 MeV) display a single-peak profile—consistent with observations from NOAA/MEPED. By fitting a Double-Gaussian distribution in both latitude and longitude from January 2019 to April 2024, we find that the center of the SAA proton distribution drifted northward at an average speed of 0.29±0.12°/yr (dayside). At the same time, the SAA proton center drifted westward at speeds of 0.36±0.08°/yr (dayside) and 0.33±0.10°/yr (nightside). Notably, lower-energy protons drift slightly faster. The geomagnetic field variations in the SAA region observed by CSES are generally consistent with the IGRF-13 model. Based on IGRF-13, we calculate drift speeds from 2015 to 2025 to be 0.014±0.002°/yr in the northward (latitudinal) direction and 0.282±0.030°/yr in the westward (longitudinal) direction. Quantitative boundary analysis further indicates that the area of the SAA decreased by 6.09%±1.03% from 2019 to 2024, showing a negative correlation with solar activity. These findings contribute to the understanding of SAA dynamics and the near-Earth radiation and electromagnetic environment during this current solar activity cycle.</p>

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Investigation of the South Atlantic Anomaly (SAA) by proton flux variabilities based on 6 years’ CSES data

  • 期刊论文

  • 发表日期：

    2025年10月22日

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  • Lu Wang,
  • Zhenxia Zhang,
  • Xinqiao Li,
  • Zhenghua An,
  • Yanbing Xu,
  • Ping Wang,
  • Hong Lu,
  • Xiaoyun Zhao,
  • Dali Zhang,
  • Xiaohua Liang,
  • Zhiqiang Ding,
  • Shujie Li,
  • Zeren Zhima,
  • Na Zhou

摘要

The central position of the South Atlantic Anomaly (SAA) has been drifting westward or northward, and the drift speeds exhibit a complex relationship with solar activity, which also affects the area of the SAA configuration. Using six years of data from the low-Earth orbit satellite CSES, we analyze the spatiotemporal evolution of the geomagnetic field and high-energy protons within the SAA during Solar Cycle 25. Low-energy protons (2.0–10.0 MeV) exhibit a characteristic double-peak structure, whereas high-energy protons (10.0–20.0 MeV) display a single-peak profile—consistent with observations from NOAA/MEPED. By fitting a Double-Gaussian distribution in both latitude and longitude from January 2019 to April 2024, we find that the center of the SAA proton distribution drifted northward at an average speed of 0.29±0.12°/yr (dayside). At the same time, the SAA proton center drifted westward at speeds of 0.36±0.08°/yr (dayside) and 0.33±0.10°/yr (nightside). Notably, lower-energy protons drift slightly faster. The geomagnetic field variations in the SAA region observed by CSES are generally consistent with the IGRF-13 model. Based on IGRF-13, we calculate drift speeds from 2015 to 2025 to be 0.014±0.002°/yr in the northward (latitudinal) direction and 0.282±0.030°/yr in the westward (longitudinal) direction. Quantitative boundary analysis further indicates that the area of the SAA decreased by 6.09%±1.03% from 2019 to 2024, showing a negative correlation with solar activity. These findings contribute to the understanding of SAA dynamics and the near-Earth radiation and electromagnetic environment during this current solar activity cycle.