Transmitter-induced modulation of subionospheric VLF signals: Ionospheric heating rather than electron precipitation
Transmitter-induced modulation of subionospheric VLF signals: Ionospheric heating rather than electron precipitation
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发射机引起的亚电离层 VLF 信号调制：电离层加热而不是电子沉淀
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
M. Spasojević
中科院分区：
文献类型：
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作者：
K. Graf;U. Inan;M. Spasojević
[1]地面甚低频发射机的受控键控具有周期性的开/关序列，从而能够探测对用于甚低频遥感的其他亚电离层甚低频探测信号的微弱但可测量的交叉调制影响。在本文中，我们重新审视以前发表的和额外的情况下，这样的事件，并确定这种交叉调制是由于电子沉淀的初步解释可能是不正确的。相反，这样的事件似乎是完全一致的电离层加热所造成的键控信号，即使探测甚低频信号路径位于数千公里的加热甚低频发射机。位于夏威夷卢阿卢阿莱的21.4 kHz发射机NPM以周期性序列键控开/关，并且在由华盛顿吉姆克里克的24.8 kHz发射机NLK生成的亚电离层传播探测信号上观察到相同的周期性。先前发表的这些实验的初步结论并没有进行详细的审查，由于缺乏明显的开始延迟和滞后时间在观察到的扰动，这消除了发射机引起的沉淀的电子辐射作为一个可能的原因。对接收机的详细测试表明，仪器交叉调制在这些观测中不是一个问题。因此，它的结论是，所观察到的扰动，尽管发生在探测信号路径，是1750公里，远离NPM在其最接近的点，是由于直接电离层加热键控甚低频发射机NPM。结果表明，甚低频发射机可能会影响上覆电离层的横向区域比以前认为的要大得多。
[1] The controlled keying of ground-based VLF transmitters with periodic on/off sequences allows the detection of weak but measurable cross-modulation effects on other subionospheric VLF probe signals used for VLF remote sensing. In this paper, we reexamine previously published and additional cases of such events and determine that the initial interpretations of such cross modulation as being due to electron precipitation is likely incorrect. Rather, such events appear to be fully consistent with ionospheric heating caused by the keyed signal, even when the probe VLF signal path lies thousands of kilometers from the heating VLF transmitter. The 21.4 kHz transmitter NPM located in Lualualei, Hawaii, is keyed on/off in periodic sequences, and that same periodicity is observed on the subionospherically propagating probe signal generated by the 24.8 kHz transmitter NLK of Jim Creek, Washington. Previous initial conclusions published for these experiments do not hold under detailed review due to the lack of discernible onset delay and lag time in the observed perturbations, which eliminates transmitter-induced precipitation of electron radiation as a possible cause. Detailed testing of the receiver shows instrumental cross-modulation to not be a concern in these observations. It is thus concluded that the observed perturbations, despite occurring on a probe signal pathway that is 1750 km away from NPM at its point of closest approach, are due to direct ionospheric heating by the keyed VLF transmitter NPM. Results indicate that the VLF transmitter may affect the overlying ionosphere over much larger lateral regions than previously believed.