Investigations in the U.S.S.R. of non-linear phenomena in the ionosphere

Investigations of non-linear ionospheric phenomena in the U.S.S.R. are reviewed. The facilities available and some non-linear phenomena first observed with these facilities are described. Among these are strong heating and non-linear absorption in lower parts of the ionosphere, self-modulation caused by intense Langmuir oscillations, the modulation of the auroral electrojet at VLF, stimulated ionization in the F-region, self-focusing effects at oblique incidence as well as many theoretical investigations of non-linear phenomena.