| Autor: |
Wang, Yongping1,2 (AUTHOR), Lu, Gaopeng2 (AUTHOR) gaopenglu@gmail.com, Cheng, Zhengwei3 (AUTHOR), Niu, Ziru2 (AUTHOR), Chen, Yazhou4 (AUTHOR), Peng, Kang‐Ming2 (AUTHOR), York, Seah Boon2 (AUTHOR), Ahmad, Mohd Riduan5 (AUTHOR) |
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| Zdroj: |
Journal of Geophysical Research. Atmospheres. 9/28/2024, Vol. 129 Issue 18, p1-16. 16p. |
| Abstrakt: |
The return stroke of cloud‐to‐ground (CG) lightning is an impulsive radiator of very low‐frequency/low‐frequency (VLF/LF) electromagnetic signals allowing for the remote sensing of lower ionosphere over large spatial coverage. In this study, we examined the LF magnetic fields measured in Malacca, Malaysia, to probe reflection heights of the lower ionosphere near the equator on three different nights in 2021. The results show that the virtual ionospheric height at nighttime typically ranged from 82.0 to 90.0 km, with a mean value of 85.3 km. Our measurements also revealed significant variations in the virtual ionospheric height across different regions over a spatial scale of about 800 km. The maximum height difference was about 5.0 km. Moreover, the fluctuation characteristics are observed in both estimated ionospheric height and calculated peak reflection ratio during similar periods. This fluctuation may be related to atmospheric gravity waves in the nighttime ionosphere. In addition, we compared the virtual ionospheric height estimated from CG strokes of different polarities, and the results showed that the virtual reflection height for positive CG strokes is lower than that for negative ones. Plain Language Summary: The ionosphere is the border zone between Earth's atmosphere and exterior space environment. The lowest part of ionosphere, at the altitude range of 60–100 km is particularly tough to measure and impacts both ground‐to‐ground and satellite‐to‐ground communications. Due to the limited coverage range of artificial very low‐frequency and low‐frequency (VLF/LF) techniques by a fixed number of transmitters, the global distribution of broadband radio atmospherics, or sferics, originating from cloud‐to‐ground (CG) lightning strokes has higher detection efficiency. These sferics propagating hundreds of kilometers provide a higher signal‐to‐noise ratio and more detailed information on the lower ionosphere. Currently, the applications of lightning‐induced electromagnetic pulses for remote sensing the lower ionosphere are primarily focused on mid‐to‐high latitude regions. Despite being a hotspot of lightning, there is still a lack of related research in the equatorial areas. Therefore, this study aims to investigate nighttime ionospheric variations using LF magnetic fields generated by lightning strokes in the equatorial region near Malacca, Malaysia, to fill the gap in this field. Our analysis reveals the variation in the virtual reflection height of the equatorial nighttime lower ionosphere by using the magnetic field information contained in lightning sferics and discusses the possible reasons for this variation. Key Points: Variation in the nighttime lower ionospheric height near the equator is estimated with the measurement of low‐frequency lightning sfericsIonospheric reflection height at night in equatorial region shows significant temporal fluctuation, similar for peak reflection ratioEstimation of nighttime lower ionospheric height appears to considerably depend on the polarity of lightning strokes [ABSTRACT FROM AUTHOR] |
| Databáze: |
GreenFILE |
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