Phenomena observed by HF long-distance diagnostic tools in the HF modified auroral ionosphere during magnetospheric substorm

摘要

The HF long-distance diagnostic tools located in St. Petersburg combined with multi- instrument observations at Tromso have been operated in conjunction with the ionospheric heating facility near Tromso to examine the heater-induced phenomena in the auroral iono- sphere. The distinctive feature of the heating experiment was the reflection of the pump wave from auroral sporadic E_s-layer. During substorm expansion, strong stimulated electromagnetic emission (SEE) at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the downshifted maxmum frequency was found. It is companied by excitation of the VLF waves penetrating into magneto- sphere and stimulating the precipitation of the energetic electrons (10-4keV) of ~1 -min dura- tion due to a cyclotron resonant interaction of the natural precipitating electrons (l - 1 0 keV) with the heater-induced whistler waves in the magnetosphere. In the recovery phase of the auroral substorm, emissions at the heater second harinomc frequency were accompamed by excitation of AFAI in the E_s layer with the large decay time up to several minutes after the heater tarn-off The possible explanation for these emissions can be found from the linear conversion process. when the pump wave of O mode may directly convert to electrostatic waves in the region ofthe HF plasma resonances. The large decay time may result from electromagnetic instability growth in the heater-modified ionosphere at the downward field-aligned currents.