Ground‐level detection of low‐ and medium‐frequency auroral radio emissions
Ground‐level detection of low‐ and medium‐frequency auroral radio emissions
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低频和中频极光无线电发射的地面探测
DOI：
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
G. Romick
中科院分区：
文献类型：
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作者：
R. Benson;M. Desch;R. Hunsucker;G. Romick
在极光区域地面探测到频率范围为几百千赫的自然射电辐射。这些测量是1986年春天在阿拉斯加费尔班克斯附近进行的一次地面观测计划中进行的，目的是探测极光回旋脉泽产生的哨声模波。对探测这种辐射的期望是基于早先关于极光射电发射的理论工作和卫星观测。四个商用通信接收器被用来获取150、291、500和700 kHz的无线电噪声频谱的窄带(3 KHz)样本。在15个晚上的操作中，有7个晚上获得了极光过程的信号。这种信号与人为干扰的区别在于它们的突发时间结构和宽带(数百千赫)和/或正交天线上类似的信号强度。与地球物理现象的一一对应关系并不总是显而易见的。即使在弱到中等的磁活动时也能观察到发射，而且在最强的磁活动期间往往没有发射。然而，大多数最强的发射是在当地时间午夜(≈±30分钟)附近的一个小时间间隔内观察到的。磁午夜附近现象的如此紧密的有序表明了与极光过程的密切联系，尽管在传统的地面地球物理记录中，产生波过程的必要条件并不容易显现。目前的结果支持过去30年文献中关于极光在100千赫兹频率上产生的无线电噪声的文献中的偶然报告，并表明将地面高纬度甚低频电台的上限频率扩大到1兆赫附近的重要性。这样的观测可以提供持续监测地面回旋脉泽产生的哨声发射的手段，进而确定在什么条件下启动这一特定的不稳定过程。
Natural radio emissions in the frequency range of several hundred kilohertz were detected at ground level in the auroral region. The measurements were made during a ground-level observing program conducted near Fairbanks, Alaska, in the spring of 1986 in an attempt to detect auroral cyclotron-maser generated whistler mode waves. The expectation for detecting such emissions was based on earlier theoretical work and satellite observations concerning auroral radio emissions. Four commercial communication receivers were used to obtain narrowband (3 kHz) samples of the radio noise spectrum at 150, 291, 500, and 700 kHz. Signals attributed to auroral processes were obtained on 7 of 15 nights of operation. Such signals were distinguished from man-made interference by their bursty time structure and wide bandwidth (hundreds of kilohertz) and/or comparable signal intensities on orthogonal antennas. A one-to-one correlation with geophysical phenomena was not always readily evident. Emissions were observed even when magnetic activity was weak-to-moderate, and they were often absent during the strongest magnetic activity. Most of the strongest emissions, however, were observed in a small time interval around midnight magnetic local time (≈ ± 30 min). Such a tight ordering of the phenomena near magnetic midnight suggests a close tie-in with auroral processes, even though the necessary conditions for the wave generation process are not readily apparent in conventional ground-based geophysical records. The present results support earlier occasional reports in the literature, over the last 3 decades, of radio noise from the aurora at frequencies ∼ 100 kHz and indicate the importance of extending the upper frequency of ground-based high-latitude VLF stations to the vicinity of 1 MHz. Such observations may provide the means to continuously monitor cyclotron maser-generated whistler emissions from the ground and, in turn, to determine under what conditions this specific instability process is initiated.