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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Excitation of short-scale field-aligned electron density irregularities by ionospheric topside sounders
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Excitation of short-scale field-aligned electron density irregularities by ionospheric topside sounders

机译：电离层顶部测深仪激励短尺度场对准电子密度不规则性

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摘要

Generation of short-scale field-aligned electron density irregularities on a short timescale (1 s) by ionospheric topside sounder pulses is studied. It is a four-wave parametric coupling process, in which a sounder-launched Z mode pump wave decays into two electron Bernstein sidebands and a geomagnetic field-aligned density irregularity. The dispersion relation of the parametric coupling process has been derived and analyzed. The results show that meter-scale field-aligned electron density irregularities (FAI) can be excited with growth rates of the order of 10~5 s~(-1) under the resonance conditions that f_0 approx= f_p approx= nf_c, where f_0, f_p, and f_c are the pump wave frequency, electron plasma frequency, and electron cyclotron frequency, respectively, and n is an integer. The excited FAI extend along the magnetic field toward the satellite path, causing the incoherent scattering of the subsequently transmitted sounding pulses. This is suggested to be a possible cause of long-duration Z mode echoes appearing on the Alouette 2 ionograms when f_0 approx= f_p approx= nf_c, as reported by Benson [1997]. It is found that the threshold field of the instability decreases with increased n. It may explain why long-duration Z mode echoes were only observed when n >= 4.
机译：研究了电离层顶部测深仪脉冲在短时间尺度（ 1 s）上产生的短尺度场对准电子密度不规则现象。这是一个四波参数耦合过程，其中，发声器发射的Z模式泵浦波衰减为两个电子伯恩斯坦边带和与地磁场对齐的密度不规则性。推导并分析了参数耦合过程的色散关系。结果表明，在f_0近似= f_p近似= nf_c的共振条件下，以10〜5 s〜（-1）的量级的增长率可以激发米级场取向电子密度不规则（FAI），其中f_0 ，f_p和f_c分别是泵浦波频率，电子等离子体频率和电子回旋加速器频率，并且n是整数。激发的FAI沿着磁场向卫星路径延伸，从而导致随后发送的探测脉冲发生非相干散射。如Benson [1997]所报道的，这被认为是当f_0近似= f_p近似= nf_c时，Alouette 2离子图上出现长时间Z模式回波的可能原因。发现不稳定性的阈值场随n的增加而减小。这可以解释为什么只有在n> = 4时才观察到长时间Z模式回波。

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