Wave characteristics of tweek atmospherics deduced from the direction-finding measurement and theoretical interpretation
Wave characteristics of tweek atmospherics deduced from the direction-finding measurement and theoretical interpretation
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DOI：
10.1029/93jd02555
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发表时间：
1994-05
影响因子：
--
通讯作者：
M. Hayakawa;K. Ohta;K. Baba
中科院分区：
文献类型：
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作者：
M. Hayakawa;K. Ohta;K. Baba
基于我们对中国南方观测到的甚低频数据的现场分析测向应用，阐明了周大气的详细波特征（入射角和方位角、波偏振及其频率依赖性）。然后发现，在其截止频率（f1c = 1.7 ∼ 1.8 kHz）之上的频率处，一阶模的波偏振总是左手性的，并且当波频率降低到f1c时，它变成精确的左手圆形，并且当频率接近f1c时，入射角变为零（垂直）。而频率低于 f1c 的零阶模式被发现是线性偏振的。首先对这些波特性进行定性解释，然后我们尝试根据地球-电离层波导中的全波理论来解释它们，其中假设了较低电离层的实际电子密度分布。最后，本文提出的波偏振测量有助于研究周尾的形成机制、闪电放电的哨声模式波的耦合、较低的电离层密度剖面等。
Detailed wave characteristics (incident and azimuthal angles, wave polarization, and their frequency dependences) of tweek atmospherics have been elucidated on the basis of the application of our field-analysis direction finding to the VLF data observed in southern China. It is then found that the wave polarization of the first-order mode at the frequency above its cutoff frequency (ƒ1c = 1.7 ∼ 1.8 kHz) is always left handed and it becomes exactly left-handed circular when the wave frequency decreases down to the ƒ1c, together with the fact the incident angle becomes zero (vertical) when the frequency approaches ƒ1c. Whereas the zeroth-order mode at frequency below ƒ1c is found to be linearly polarized. These wave properties are first interpreted qualitatively, and then we try to explain them in terms of the full wave theory in the Earth-ionosphere waveguide in which the realistic electron density profiles of the lower ionosphere are assumed. Finally, it is suggested that the measurement of wave polarization, as given in this paper, would be useful in studying the formation mechanism of tweek tails, the coupling into whistler mode waves of lightning discharges, the lower ionospheric density profile, etc.