Resonant Cavities and Waveguides in the Ionosphere and Atmosphere
Resonant Cavities and Waveguides in the Ionosphere and Atmosphere
复制标题
DOI：
10.1029/169gm19
复制
发表时间：
2013-03
期刊：
影响因子：
--
通讯作者：
R. Lysak;A. Yoshikawa
中科院分区：
文献类型：
--
作者：
R. Lysak;A. Yoshikawa
电离层和邻近区域等离子体参数的强烈不均匀性可以捕获ULF范围（Pcl/Pil）上端的波。顶侧电离层的特点是迅速增加的阿尔芬速度与规模的高度约为1000公里。剪切模式阿尔芬波在这个区域可以部分地被困在0.1-1.0 Hz范围内的频率。相同的结构可以捕获该频带中的快模压缩波。由于这些波可以穿过磁场线传播，因此该结构构成波导，其中能量可以以与阿尔芬速度相当的速度传播，通常大约为1000 km/s。电离层中的霍尔效应耦合这两种波模式，使得通过剪切模式阿尔芬波引入场对准电流可以激发可以在波导中传播的压缩波。在无限大的电离层电导率的限制下，这些波从大气场中分离出来;然而，对于有限的电导率，电离层和大气波是耦合的。大气中的横磁模可以在超低频下传播，并与基频为8 Hz的大气形成整体舒曼共振。有人认为，在风暴突然开始期间，通过这种大气波导以光速传播的信号可以迅速将信号从极地地区传输到低纬度地区。
The strong inhomogeneities in plasma parameters in the ionosphere and adjacent regions can trap waves in the upper end of the ULF range (Pcl/Pil). The topside ionosphere is characterized by a rapidly increasing Alfven speed with a scale height on the order of 1000 km. Shear-mode Alfven waves in this region can be partially trapped at frequencies in the 0.1-1.0 Hz range. The same structure can trap fast-mode compressional waves in this frequency band. Since these waves can propagate across magnetic field lines, this structure constitutes a waveguide in which energy can propagate at speeds comparable to the Alfven speed, typically on the order of 1000 km/s. Hall effects in the ionosphere couple these two wave modes, so that the introduction of a field-aligned current by means of a shear-mode Alfven wave can excite compressional waves that can propagate in the waveguide. In the limit of infinite ionospheric conductivity, these waves are isolated from the atmospheric fields; however, for finite conductivity, ionospheric and atmospheric waves are coupled. Transverse magnetic modes in the atmosphere can propagate at ULF frequencies and form global Schumann resonances with the fundamental at 8 Hz. It has been suggested that signals that propagate at the speed of light through this atmospheric waveguide can rapidly transmit signals from the polar region to lower latitudes during sudden storm commencements.