100 days of ELF/VLF generation via HF heating with HAARP
100 days of ELF/VLF generation via HF heating with HAARP
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DOI：
10.1002/jgra.50558
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发表时间：
2013-10-01
影响因子：
2.8
通讯作者：
Golkowski, M.
中科院分区：
文献类型：
--
作者：
Cohen, M. B.;Golkowski, M.
极低频/甚低频（ELF/VLF）无线电波很难用传统的天线产生。电离层高频（HF）加热设施通过调制电离层下层的加热产生ELF/VLF波。电离层的高频加热改变了电离层较低的电导率，当加热在极低频/极低频频率调制时，电离层电导率在自然电流（如极光电喷流）的存在下会在天空中产生天线。本文总结了在阿拉斯加加科纳附近3.6MW高频主动极光研究计划（HAARP）设施中近100天的ELF/VLF波产生实验，在各种ELF/VLF频率，季节和一天中的时间。我们提供了在附近站点观测到的500- 3500hz波段产生的ELF/VLF磁场的综合统计数据。具有特定高频波束配置（3.25 MHz，垂直波束，调幅）的传输被隔离，因此数据比较是自一致的，跨越近500万次音调或频率时间斜坡的单个测量。在接近当地午夜时，平均发电量有一个最小值。研究发现，局部夜间的发电平均较弱，但变化较大，有少数很强的发电周期。每天的信号幅度可能相差20-30dB。在传输的最初大约30分钟内，产生增强了大约5dB，这可能是持续高频加热引起的缓慢电子密度变化的标志。理论计算将观察到的振幅与注入波导的功率联系起来，达到250公里。在这个基线配置（垂直波束，3.25 MHz，调幅）中，HAARP产生并注入波导的中位功率约为0.05-0.1 W，但可能在短时间内产生数百瓦的功率。几项效率改进进一步提高了极低频/甚低频波的产生效率。
Extremely low frequency/very low frequency (ELF/VLF) radio waves are difficult to generate with conventional antennas. Ionospheric high frequency (HF) heating facilities generate ELF/VLF waves via modulated heating of the lower ionosphere. HF heating of the ionosphere changes the lower ionospheric conductivity, which in the presence of natural currents such as the auroral electrojet creates an antenna in the sky when heating is modulated at ELF/VLF frequencies. We present a summary of nearly 100days of ELF/VLF wave generation experiments at the 3.6MW High Frequency Active Auroral Research Program (HAARP) facility near Gakona, Alaska, at a variety of ELF/VLF frequencies, seasons, and times of day. We present comprehensive statistics of generated ELF/VLF magnetic fields observed at a nearby site, in the 500-3500 Hz band. Transmissions with a specific HF beam configuration (3.25 MHz, vertical beam, amplitude modulation) are isolated so the data comparison is self-consistent, across nearly 5 million individual measurements of either a tone or a piece of a frequency-time ramp. There is a minimum in the average generation close to local midnight. It is found that generation during local nighttime is on average weaker but more highly variable, with a small number of very strong generation periods. Signal amplitudes from day to day may vary by as much as 20-30dB. Generation strengthens by approximate to 5dB during the first approximate to 30min of transmission, which may be a signature of slow electron density changes from sustained HF heating. Theoretical calculations are made to relate the amplitude observed to the power injected into the waveguide and reaching 250 km. The median power generated by HAARP and injected into the waveguide is approximate to 0.05-0.1 W in this baseline configuration (vertical beam, 3.25 MHz, amplitude modulation) but may have generated hundreds of watts for brief durations. Several efficiency improvements have improved the ELF/VLF wave generation efficiency further.