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低纬电离层人工调制所激发的ELF波射线追踪
Raytracing of extreamely low frequency waves radiated from ionospheric artificial modulation at low latitude
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摘要: 通过大功率极低频（ELF）／甚低频（VLF）高频调幅波能有效地扰动低电离层电流，形成等效的ELF／VLF电离层虚拟天线，辐射ELFNLF波，所辐射出的低频信号能够传播进入到磁层，对其传播特性的研究对于理解辐射带高能电子沉降具有重要意义．本文基于磁层射线追踪理论，通过数值模拟得到在低纬地区所激发出的ELF波在磁层中的射线路径，并对其特征进行分析．数值模拟结果表明，从低纬激发的ELF波在南北半球来回弹跳，并逐渐传播到更远处，对于不同频率的ELF波，频率越高，传播距离越近，频率越低，传播距离越远，在传播过程中，ELF波会逐渐倾向于在一个固定的磁层区域附近来回反射，在此过程中波法向角也逐渐变为90°，射线方向倾向于沿着背景磁场方向传播．Abstract: Powerful high-frequency radio waves modulated at extremely low frequency (ELF) and very low frequency (VLF) can efficiently modify the lower ionospheric current which can act as an equivalent ionospheri'c antenna for the generation of ELF/VLF wave and these signals can propagate into the magnetosphere and the investigation of the propagation properties is of significance for understanding of radiation belt energetic electrons precipitation. In this paper, based on the raytracing theory, the ray paths of ELF waves in the magnetosphere are obtained using numerical modeling and the properties are analyzed. The results shows that the ELF waves generated from the low latitude reflect between the southern and northern hemisphere and propagate to the farther place gradually. For the signals with different frequencies, the higher their frequencies, the shorter their propagation distances are, the lower their frequencies, the longer their propagtion distances are. In the process, ELF waves tend to reflect near a fixed region. The normal angel increases to 90° gradually and ray direction tends to propagate along the direction of geomagnetic field.
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