Peculiarities in the evolution of the BUM of stimulated radio emission of the ionosphere

We present measured spectral and dynamic characteristics of the broad upshifted maximum (BUM) in the spectrum of artificial ionospheric radio emission (AIRE). It is shown that BUM is already formed starting from pump-wave frequencies that are smaller by at least 10 kHz than the values of electron gyrofrequency harmonic nf_He determined by the disappearance of the principal downshifted maximum (DM) in AIRE spectrum. The characteristics of additional maxima in BUM spectrum, which are a multiple of its principal maximum, are studied. It is shown that the frequency of BUM intensity maximum does not depend on the pump-wave frequency and the characteristic times of its evolution increase sharply for f_PW close to nf_He. We discuss the possibility of existence of the fast and slow components in BUM spectrum, which have significantly different evolution times. Experimental results on BUM behavior for different regimes of ionosphere modification are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 3, pp. 352–371, March, 1996.The authors thank the staff of the Sura heating facility for assistance in organizing and running the experiments. The Russian authors also thank the Russian Foundation for Fundamental Research (grants 94-02-03253a and 96-02-18659), Soros Foundation (grants R87000 and 020623), and Ministry of Science for financial support of this paper and the Sura heating facility.