Directional features of the downshifted peak observed in HF-induced stimulated electromagnetic emission spectra obtained using an interferometer

摘要

A high frequency (HF) ionospheric modification experiment was carried outbetween 25 September and 8 October 2004, using the EISCAT HF transmitterlocated near Tromsø, Norway. During this experiment the spectra of thestimulated HF sideband waves (stimulated electromagnetic emission or SEE)induced by the HF pump were observed using an interferometer consisting ofthree spaced receiving antennas with baselines both along and perpendicularto the meridian, and a multi-channel coherent receiver, installed in thevicinity of the HF facility. The transmitter operated at 4040kHz and itsantenna beam was scanned to angles of 0°, 7°, 14°, and 21°south from vertical, pausing 4min at each position. This paper focuses onfeatures of the downshifted peak (DP) emission, which has not been asthoroughly studied as many of the other SEE spectral features observablewithin the EISCAT pump frequency range. It was found that thesignal-weighted direction of the DP source region remained within 5° ofmagnetic zenith as the HF beam was tilted between 0 and 21° south of vertical.