Active Modification of the Ionosphere

1993年日本学年，在美国阿拉斯加州费尔班克斯附近的高能极光刺激（HIPAS）设施举行了两次美日联合电离层改造实验活动，对各种诊断技术进行了测试，并开发了在电离层改造实验中有效协调它们的方法。在电离层改造实验中，大功率地面高频发射机被用来诱导电离层的大尺度和小尺度变化。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，约束时间长，这使得电离层等离子体与传统的实验室等离子体有明显的区别。我们HIPAS活动的成就总结如下。极低频和极低频波的激发极低频和极低频波的激发是利用强高频波的热效应，通过改变等离子体的电导率来调制极性电喷电流。为了探测质子回旋波频率范围（ELF）和哨声波频率范围（VLF）信号，进行了卫星和地面观测。为了测量高频加热区的高度和范围，建立了一个由8个偶极子天线组成的热计系统。这种测量对于定位极低频和甚低频波的源区域至关重要。据我们所知，这是第一次与电离层改变实验一起进行的距离计测量。高频多普勒测量也使用低功率高频波，其频率与加热器高频波略有不同，作为测试波。新的诊断技术，如高频相控阵雷达和高频激光雷达系统，进行了测试。

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.