Influence of small-scale irregularities on features of the overshoot effect in the temporal evolution of stimulated electromagnetic emission. Part II. Relaxation stage

We present the results of experimental studies of the evolution of diagnostic stimulated electromagnetic emission of the ionosphere (DSEE) in a broad range of the pump and probing wave frequencies under sounding of the F-layer disturbed by powerful HF radio waves. We study the parameters of the overshoot effect in SEE evolution during the relaxation stage of artificial small-scale irregularities and show that the amplification of DSEE (inverse overshoot effect) is related to the relaxation of the anomalous attenuation due to scattering at these irregularities. We have found that the characteristic time scales of development of the overshoot effect decrease and its value increases as the pump wave frequency decreases from 6 to 4 MHz and as the probed volume moves from the edge to the central part of the disturbed volume. We relate the effects observed to the increasing intensity of the irregularities with scales l_∼∼3−10 m. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 810–824, August 1999.