Excitation of Alfven waves and vortices in the ionospheric Alfven resonator by modulated powerful radio waves

A review of the artificial excitation of Alfven waves and vortices in the i onospheric Alfven resonator (IAR) is presented. In the framework of simplif ied models of the IAR and the Alfven vortex instability, we discuss the mai n physical phenomena arising under the periodic heating of the ionosphere b y a powerful HF radio signal with a modulation frequency F which lies in th e range of short-period geomagnetic pulsations (F = 0.1-10 Hz). The amplitu des, frequency spectra, and polarization characteristics of artificial puls ations on the ground are found, and a brief comparison with experimental da ta is made. The Alfven vortex instability in the IAR is analysed from the p oint of view of its artificial triggering. Two ways of such a triggering ar e discussed. The first suggests the use of two spaced transmitter antenna w hich produce an ionospheric current being in resonance with Alfven vortices . Existing heating facilities are suitable for this experiment. The second method is based on the change of macroscopic parameters of the ionosphere, such as the conductivity in the instability region. This method is simple, but requires more powerful heaters. (C) 2000 Elsevier Science Ltd. All righ ts reserved.