Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location
Abstract
:1. Introduction
2. Data and Methods of Analysis
3. Results
4. Discussion
5. Conclusions
- The peak of τ appeared at noon, consistent with previous studies on equatorial latitudes.
- There is a post-sunset peak in τ observed during the winter and equinox, and it means that NmF2 is decreasing faster than TEC, which can be associated with the higher post-sunset TEC enhancement occurrence in equinox/winter, proving previous conclusions. In addition, the τ continues to decrease after post-midnight and the equinoctial one is smallest due to the largest nighttime NmF2 enhancement in equinox and the faster decrease in TEC in equinox than that in solstice.
- The dependence of τ on the solar activity are different for daytime and nighttime: the daytime τ seems to increase with solar activity, as TEC is more sensitive to the solar activity than NmF2, whereas the nighttime one decreases with solar activity at night, and it should be due to the fact the H+-O+ transition height in the low solar activity is lower than that in the high solar activity at night.
- The τ has more variability during nighttime than daytime, during both the geomagnetically quiet and disturbed conditions, and the greatest variability of τ appeared at sunrise.
- The τ at noon is larger in winter and equinox than in summer. It is probably due to the absence of NmF2 noontime bite-out in summer at this region.
- There is no pre sunrise peak in τ and τ get low values during the pre-sunrise period at Guam. However, previous studies indicate that pre sunrise peak is a widely observed feature, from low to high latitude, and τ even reaches maximum at sunrise for specific seasons. The contradiction is probably due to Guam being located at equatorial latitude, as the low values in the pre sunrise period could also be seen at other longitudinal equatorial latitude station. In addition, longitudinal difference might also contribute to the difference.
- The geomagnetic storm seems to have a positive effect on the τ during most of the storm period in Guam, except at sunrise period, when the τ attains large variability, even at the geomagnetically quiet condition. This study also provides a new physical explanation for the observed effect of geomagnetic storm on τ in Guam. During the positive storms, the penetration electric field along with storm time equator-ward neutral wind tends to increase upward drift and uplift F region, causing the large increase in TEC accompanied by relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC, which does not undergo severe depletion as NmF2 does during the negative storms. Therefore, the geomagnetic storm seems to enhance τ both during the positive and negative ionospheric storms.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Year | Seasons | Mean Daytime Values of τ (km) | Mean Nighttime Values of τ (km) |
---|---|---|---|
2014 | Winter | 388.9 | 232.1 |
Summer | 303.9 | 188.9 | |
Equinox | 364.6 | 250.7 | |
2016 | Winter | 299.3 | 255.5 |
Summer | 288.6 | 238.5 | |
Equinox | 301.2 | 268.4 |
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Zhang, Y.; Wu, Z.; Feng, J.; Xu, T.; Deng, Z.; Ou, M.; Xiong, W.; Zhen, W. Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location. Remote Sens. 2021, 13, 5175. https://doi.org/10.3390/rs13245175
Zhang Y, Wu Z, Feng J, Xu T, Deng Z, Ou M, Xiong W, Zhen W. Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location. Remote Sensing. 2021; 13(24):5175. https://doi.org/10.3390/rs13245175
Chicago/Turabian StyleZhang, Yuqiang, Zhensen Wu, Jian Feng, Tong Xu, Zhongxin Deng, Ming Ou, Wen Xiong, and Weimin Zhen. 2021. "Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location" Remote Sensing 13, no. 24: 5175. https://doi.org/10.3390/rs13245175