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<p>The ionospheric irregularities in the East Asian sector mainly occur in the equinox months, but they also occur occasionally in the solstice months, that is, the unseasonal ionospheric irregularities. The study of the morphology and mechanism of this kind of unseasonal irregularities has been a hot topic in recent years. Using the rate of the TEC index (ROTI) map derived from the observation of multiple GNSS receiver network in China, combined with observations from four ionosondes located in Hainan and Guangzhou, the ionospheric irregularities that occurred in China’s low-latitude region during the geomagnetic quiet period on July 5 and 17, 2013 are studied, and their spatiotemporal evolution during these two events is provided. Unlike the irregularities in equinox months, both concerned events occurred near midnight, and when the irregularities appear above the ionosonde station, the range spread F emerges in the ionograms. Comparatively, the irregularities on July 5 mainly appear before midnight, while the irregularities on July 17 were present both before and after midnight, and the intensity and range of the irregularities on July 5 are greater than those on July 17. The irregularities can be identified as two discrete patches located on the east and west sides in both events. They initially appeared at lower latitudes and gradually drifted northeastward, roughly drifting from the region of 15°N and 105°E to the region of 25°N and 125°E. The eastward drift velocity on July 5 and 17 is estimated to be about 32 and 39 m/s, respectively. In addition, it is noted that the irregularities exhibit a little southward drifting in the final evolving stage in both events, which may be related to the meridional wind in the thermosphere. During and before the irregularities, the increase of the ionospheric foF2 and TEC is observed, but the pre-sunset reversal enhancement or the increase of hmF2 that is favorable for the development of irregularities is not observed. Considering the relatively quiet geomagnetic conditions during these two events, the reason for these two irregularities cannot be determined.</p>

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Case studies of the unseasonal ionospheric irregularities in China’s low latitude on July 5 and July 17, 2013

  • 期刊论文

  • 发表日期：

    2025年10月13日

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  • Hongyu Gao,
  • Donghe Zhang,
  • Yabin Zhang,
  • Yaoyu Tian,
  • Ke Li,
  • Guanglin Yang,
  • Shuji Sun,
  • Xiukuan Zhao,
  • Guozhu Li,
  • Guojun Wang

摘要

The ionospheric irregularities in the East Asian sector mainly occur in the equinox months, but they also occur occasionally in the solstice months, that is, the unseasonal ionospheric irregularities. The study of the morphology and mechanism of this kind of unseasonal irregularities has been a hot topic in recent years. Using the rate of the TEC index (ROTI) map derived from the observation of multiple GNSS receiver network in China, combined with observations from four ionosondes located in Hainan and Guangzhou, the ionospheric irregularities that occurred in China’s low-latitude region during the geomagnetic quiet period on July 5 and 17, 2013 are studied, and their spatiotemporal evolution during these two events is provided. Unlike the irregularities in equinox months, both concerned events occurred near midnight, and when the irregularities appear above the ionosonde station, the range spread F emerges in the ionograms. Comparatively, the irregularities on July 5 mainly appear before midnight, while the irregularities on July 17 were present both before and after midnight, and the intensity and range of the irregularities on July 5 are greater than those on July 17. The irregularities can be identified as two discrete patches located on the east and west sides in both events. They initially appeared at lower latitudes and gradually drifted northeastward, roughly drifting from the region of 15°N and 105°E to the region of 25°N and 125°E. The eastward drift velocity on July 5 and 17 is estimated to be about 32 and 39 m/s, respectively. In addition, it is noted that the irregularities exhibit a little southward drifting in the final evolving stage in both events, which may be related to the meridional wind in the thermosphere. During and before the irregularities, the increase of the ionospheric foF2 and TEC is observed, but the pre-sunset reversal enhancement or the increase of hmF2 that is favorable for the development of irregularities is not observed. Considering the relatively quiet geomagnetic conditions during these two events, the reason for these two irregularities cannot be determined.