| 甚低纬哨声低电离层透射过程的数值模拟 |
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| 引用本文： | 吴向阳,长野勇.甚低纬哨声低电离层透射过程的数值模拟[J].地球物理学报,1996,39(5):588-600. |
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| 作者姓名： | 吴向阳 长野勇 |
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| 作者单位： | 武汉大学空间物理系, 武汉 430072;
2. 金泽大学电子与计算机工程系，金泽，920，日本 |
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| 摘 要： | 利用全波解算法模拟哨声波束在甚低纬地区黎明前低电离层透射的三维能量分布，依据波场能量和偏振分布及其对波参量和电子浓度剖面的依赖特征，分析了哨声透射、反射及与大地－电离层波导耦合过程．结果表明，哨声模波存在于９０ｋｍ以上高度，吸收、反射、波束扩展及波模转换主要发生于电离层底部８０－９０ｋｍ区间；到达地面的透射能量密度衰减２０ｄＢ以上，透射衰减随频率变化不大，但随波入射角呈不对称变化；距透射区１５０ｋｍ以外区域的测向方位角有很大偏差；入射波能量的很少一部分（对５ｋＨｚ约为－２５ｄＢ）被反射并激发起哨声模波，反射波束能量集中于入射波束附近，并随频率下降而迅速增强．计算也表明，地面接收到的甚低纬哨声回波可能与使回波向极侧偏移的电离纬向梯度有关．
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| 关 键 词： | 低纬哨声 全波解 甚低频测向 |
NUMERICAL SIMULATION OF THE WHISTLER PENETRATION PROCESS THROUGH THE LOWER IONOSPHERE AT VERY-LOW-LATITUDE |
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| WU XIANG-YANG, BAO ZONG-TI.NUMERICAL SIMULATION OF THE WHISTLER PENETRATION PROCESS THROUGH THE LOWER IONOSPHERE AT VERY-LOW-LATITUDE[J].Chinese Journal of Geophysics,1996,39(5):588-600. |
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| Authors: | WU XIANG-YANG BAO ZONG-TI |
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| Institution: | 1. Department of Space Physics, Wuhan University, Wuhan 430072, China;
2. Department of Electrical and Computer Engineering, Kanazawa University, Kanazawa 920, Japan |
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| Abstract: | By the full-wave algorithm with Fourier synthesis, 3-D propagation of whistler beam incident on the pre-dawn lower ionosphere at very low latitude is numerically investigated. Processes of transmission, reflection, and coupling with the Earth-ionosphere waveguide are discussed via the wave energy and polarisation distributions and their dependence on the wave parameters and the ionospheric profile. It is shown that the dominant wave above 90km has the propagation characteristics of the whistler mode, and the absorption, spreading, reflection and mode conversion mainly occur at and are greatly affected by the bottom of the ionosphere. It is found that the transmitted energy density along the Earth's surface is reduced by 20 dB or more. Beam transmission loss varies asymmetrically with its incident angle, but changes little with the frequency. In the region 150 km （for 5 kHz） away from the“exit area”where whistlers emerges, the bearing measurements using ground-based VLF direction-finders may be in error. Only a small portion （about-25 dB at skHz） of the incident energy is reflected up to the altitude of 150 km, and major reflection takes place in a small range of altitude at the bottom of the ionosphere with little spreading and lateral shift with respect to the incident beam. Reflection is enhanced considerably at lower frequency. Our results also suggest that an ionospheric gradient refracting waves to higher latitudes would be favorable factor for multi-hop echoes to be received on the ground. |
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| Keywords: | Low-latitude whistler Full-wave solution Direction-finding |
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