Simultaneous observations of ELF waves from an artificially modulated auroral electrojet in space and on the ground
Simultaneous observations of ELF waves from an artificially modulated auroral electrojet in space and on the ground
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DOI：
10.1029/ja089ia03p01655
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发表时间：
1984-03
影响因子：
--
通讯作者：
H. G. James;R. Dowden;M. Rietveld;P. Stubbe;H. Kopka
中科院分区：
文献类型：
--
作者：
H. G. James;R. Dowden;M. Rietveld;P. Stubbe;H. Kopka
1981年12月9日，在挪威特罗姆索附近的Max-Planck-Institut Fur Aeronomie电离层加热器上空飞行时，在地面和ISIS 1号航天器的甚低频接收器中同时观测到频率在525至5850赫兹的无线电波。加热器载波频率为4.04 MHz，使用一组四个频率进行幅度调制：525、1725、2925和4125赫兹。卫星检测到了所有这些基频加上525赫兹和2925赫兹分量的谐波，这是由载波的非正弦调制引起的。沿卫星轨道接收到的信号的特征与特罗姆索周围电离层模型的三维射线跟踪结果大致一致。基于峰值相对较低的实时数据的电离层密度模型对信号的时间色散进行了最好的拟合。利用等离子体偶极子理论和从三维射线解获得的波极化信息，将观测到的信号能级转换为功率流。通过使用感应D/E区电流的磁等离子体偶极子理论，观测到的能级对应于约1.0A到100A之间的有效偶极电流产生的辐射。几何光学理论还预测了射线到达接收区极限点附近的给定卫星点的两种解，以及对应于焦散表面的北极限值。用几何光学理论预测了在该区域观察到的信号衰落的频率，但不能预测衰落深度。同时的地面观测对应于大约1A或更小的源区电流。此外，地面观测到的ELF波与ISIS上观测到的ELF波具有不同的谐波信号比和小得多的起伏。
Radio waves at frequencies between 525 and 5850 Hz were observed simultaneously on the ground and in the VLF receiver of the ISIS 1 spacecraft during a flight over the Max-Planck-Institut fur Aeronomie ionospheric heater near Tromso, Norway, on December 9, 1981. The heater carrier frequency, 4.04 MHz, was amplitude modulated with a set of four frequencies: 525, 1725, 2925, and 4125 Hz. The satellite detected all these fundamental frequencies plus harmonics of the 525 Hz and 2925 Hz components, caused by the nonsinusoidal modulation of the carrier. Characteristics of the signal received along the satellite track are in approximate agreement with the results of three-dimensional ray tracing applied to a model of the ionosphere around Tromso. The time dispersion of the signals is best fitted with an ionospheric density model based on real time data with relatively low peak values. Observed signal levels have been transformed to power flux by using a plasma dipole theory and wave polarization information obtained from the three-dimensional ray solutions. Through the use of a magnetoplasma dipole theory for the induced D/E region current, the observed levels are found to correspond to radiation created by effective dipole currents between about 1.0 and 100 A. The geometrical optics theory also predicts two solutions for rays reaching a given satellite point near the polar limit of the reception zone, and a northern limit corresponding to a caustic surface. The frequencies of signal fades observed in this region are also predicted by the geometrical optics theory, but the fade depths are not. Simultaneous ground observations correspond to source region currents of about 1 A or less. Also, the ELF waves observed on the ground have different harmonic signal ratios and much smaller fluctuations than those observed on ISIS.