Ionospheric modification experiments with the Arecibo Heating Facility

Abstract

The results obtained with ionospheric modification experiments over the three years preceding the XXI General Assembly of URSI in 1984 at Florence are reviewed. The topics discussed include weak electromagnetic sidebands observed using a single pump frequency, the HF-induced plasma line at 3.175 MHz and its similarity to the plasma lines observed using higher HF frequencies near Tromsø, the HF-enhanced plasma line observed with the 50 MHz radar, the HF-induced plasma line with a doublehumped spectrum below threshold. HF-induced plasma line spectra with height discrimination using a new technique, the HF-induced plasma line and ion line spectra obtained with two pumps differing in frequency by a few kHz, narrow features such as the OTSI in the HF-enhanced plasma line and ion line spectra observed by a new technique, the use of such narrow features for measuring the line-of-sight electron drift velocity, the discovery of a radical qualitative change in the spectrum of the HF-induced plasma line as the HF power (CW) is increased or as the duty cycle is changed while pulsing, observations of the temporal development of the enhancement of the thermal plasma line at the peak of the F2-layer by electrons accelerated during ionospheric heating studies of artificial density stratification resulting from the standing wave nature of the heating wave and strong electromagnetic sidebands generated by two Powerful HF radio waves differing from each other by some tens of Hz. Theoretical work on soliton formation and on VLF generation by HF heating is briefly mentioned, as well as experimental studies of self-focusing by observing the scintillation of extraterrestrial radio sources, direct conversion and studies of short scale field-aligned irregularities by VHF radar backscatter during ionospheric modification.