Active Modification of the Ionosphere

1993年日本学年期间，在美国阿拉斯加州费尔班克斯附近的高能极光刺激（HIPAS）设施中，美日联合进行了两次电离层改造实验活动。试验了各种诊断技术，并开发了在电离层改造实验期间有效协调这些技术的方法。在电离层改造实验中，高功率地面高频发射机用于引起电离层的大规模和小规模变化。因此，可以研究各种重要的等离子体现象，如非线性波现象和等离子体加热效应。电离层等离子体没有壁和长的约束时间使得电离层等离子体与传统的实验室等离子体截然不同。ELF和VLF波的激发ELF和VLF波是通过利用强HF波的加热效应修改等离子体电导率来调制极性电射流电流而激发的。进行了卫星和地面观测，以探测极低频（质子回旋频率范围）和甚低频（哨声波频率范围）信号。为了测量高频加热区的高度和范围，建立了一个具有八个偶极天线阵列的Riometer系统。这种测量对于定位ELF和VLF波的来源区域至关重要。据我们所知，这是第一次结合电离层改造实验进行的riometer测量。还使用频率与加热器HF波的频率略有不同的低功率HF波作为测试波进行HF多普勒测量。测试了高频相控阵雷达和高频激光雷达系统等新的诊断技术。

US-Japan joint ionospheric modification experimental campaigns were held twice during the 1993 Japanese academic year at the HIgh-Power Auroral Stimulation (HIPAS) Facility near Fairbanks, Alaska, U.S.A. Various diagnostic techniques were tested, and the method to efficiently coordinate them during ionospheric modification experiments were developed.In ionospheric modification experiments, high-power ground-based HF transmitters are used to induce large-scale, as well as small-scale, changes in the ionosphere. Various important plasma phenomena, such as nonlinear wave phenomena and plasma heating effects, can thus be investigated. The absence of walls and the long confinement time make the ionospheric plasma distinctively unique and different from conventional laboratory plasmas.Achievements from our HIPAS campaigns are summarized below.1. Excitation of ELF and VLF wavesELF and VLF waves are excited by modulating the polar electrojet current through the modification of plasma conductivities using the heating effect of powerful HF waves. Satellite, as well as ground-based, observations were carried out in order to detect ELF (proton cyclotron frequency range) and VLF (whistler wave frequency range) signals.2. Riometer observationsA riometer system with an array of eight dipole antennas was set up in order to measure the height and extent of the HF heated region. This measurement is vital in locating the region which is the source of ELF and VLF waves. To our knowledge, this is the first riometer measurement conducted in conjunction with ionospheric modification experiments. HF Doppler measurements were also performed using a low-power HF wave, whose frequency is slightly different from that of the heater HF wave, as a test wave.3. New diagnostic techniques, such as HF phased-array radar and HF lidar systems, were tested.