P. Stubbe et al., STIMULATED ELECTROMAGNETIC EMISSIONS AND ANOMALOUS HF WAVE ABSORPTIONNEAR ELECTRON GYROHARMONICS, J GEO R-S P, 99(A4), 1994, pp. 6233-6246
Simultaneous observations are presented of stimulated electromagnetic
emission (SEE) spectra and the anomalous absorption of a diagnostic HF
wave, caused by powerful radio waves generated by the Tromphi heating
facility. The pump frequency was varied in small steps around the thi
rd, fourth, and fifth harmonic of the electron gyrofrequency. Systemat
ic variations with pump frequency were observed in the anomalous absor
ption data and the entirety of SEE properties. The anomalous absorptio
n exhibits a pronounced minimum at a certain pump frequency near (or a
t) the gyroharmonic in question. Of the SEE properties the strength an
d discreteness of the downshifted maximum and the width of the downshi
fted continuum minimize together with the anomalous absorption. Other
SEE properties (namely the broad upshifted maximum, the downshifted pe
ak, and the broad symmetrical structure) exist only in well-defined na
rrow pump frequency ranges near the absorption minimum. Significant qu
antitative and qualitative differences are found between the SEE prope
rties around the third gyroharmonic on the one hand, and the fourth an
d fifth gyroharmonics on the other hand.