Spectral structure of stimulated electromagnetic emissions between electron cyclotron harmonics

Abstract

Experimental results concerning the spectrum of stimulated electromagnetic emissions (SEE) in the sidebands of a powerful high‐frequency electromagnetic ordinary mode pump wave are presented. The pump wave was vertically injected into the ionospheric F region from the Sura ionospheric modification facility in Russia. We report detailed measurements of the commonly observed continuum, downshifted maximum, and broad upshifted maximum emissions for pump frequencies ranging from the fourth to above the seventh electron cyclotron harmonic in the ionospheric plasma as well as observations of a new wideband emission occurring primarily in the upper sideband. The dependence of the SEE spectral structure on the pump frequency in relation to electron cyclotron harmonics is emphasized. All spectral features in the sidebands of the pump exhibit cyclotron harmonic effects.

Spectral features of stimulated electromagnetic emission, measured in the 4.3–9.5 MHz pump wave frequency range

“…shifted maximum (BUM), occurring in the SEE spectra in a frequency range of about A f + _ 15-150 kHz when the PW frequency is close to an electron cyclotron harmonic frequency, n fee (in our experiments, fee • 1.35 MHz, and n = 4-7 is the harmonic mode number) [Leyser et al, 1990[Leyser et al, , 1993Stubbe et al, 1994;Frolov et al, 1996Frolov et al, , 1998], and the broad upshifted structure (BUS), which is a wideband emission generated in a frequency range of about Af + • 15-100 kHz when f0 is somewhat higher than nf• [Frolov et al, 2000].…”

“…An important characteristic of all SEE features is the crucial dependence of their properties on the PW frequency when the latter is close to a gyroharmonic frequency, fo • nf• [Leyser et al, 1993[Leyser et al, , 1994Frolov et al, 1996Frolov et al, , 1998]. According to Stubbe et al, [1994], all SEE components may be divided into "gyrofeatures", which exist only when fo -n f•e, and "universal features", which exist for all pump frequencies, but may strongly change their properties if fo -nfce.…”

Numerical simulation studies on the broad upshifted maximum of ionospheric stimulated electromagnetic emission

“…The BUM is one of the most prominent upshifted features in the SEE spectrum and has been the subject of intensive investigation in past ionospheric modification experiments [Leyser et al, 1989[Leyser et al, , 1993Stubbe et al, 1994;Frolov et al, 1996Frolov et al, , 1997Frolov et al, , 1998Wagner et al, 1999]. The BUM is a broad upshifted sideband extending more than 100 kHz above the pump frequency and develops only when the pump frequency w0 is in the vicinity of harmonics of the electron cyclotron frequency, nf•½e.…”

Theoretical model for long time stimulated electromagnetic emission generation in ionospheric radio modification experiments

“…The most important of these features is the broad upshifted maximum (BUM). It occurs when f0 is within some tens of kHz above nfc• and the frequency of its maximum, fsuM, appears to satisfy the formula [Leyser et al, 1990[Leyser et al, , 1993 fBUM --fo '•' fo --llfce.…”

“…Figure 3b, 3c, and 3d of Leyser et aL [1993], showing a peak downshifted 10-15 kHz from the HF frequency. Detailed features of the DM are described by Leyser et al [1993Leyser et al [ , 1994 The føllowing may be emphasized:…”