On the morphology of Stimulated Electromagnetic Emission spectra in a wide pump wave frequency range

Results of systematic study of Stimulated Electromagnetic Emission (SEE) steady state spectrum dependence on the pump wave frequency f0 are presented. Investigations of the HF-pumped ionosphere were performed at the SURA facility for the frequency range 4.3 < f0 < 9.5 MHz with stepping of 1-50 kHz including the vicinities of the electron gyroharmonics nfce from n = 4 to 7. The results are based on the data collected during 1996-2004. The main tendencies in a behavior of the most prominent SEE spectral features (their peak and total intensities, and positions in the spectrum) versus f0 are established and studied in detail. A comparative analysis of peculiarities of different spectral features allows to improve a determination of the electron gyrofrequency in the ionosphere from the SEE spectra, as well as provides a base for deeper understanding nonlinear processes in the pump-driven upper hybrid turbulence responsible for the SEE generation.