Effect of a heated patch of auroral ionosphere on VLF-radio wave propagation

Abstract

In the early 1960s, during the period of atmospheric nuclear tests, much theoretical interest developed in the effects of localized ionospheric depressions on the propagation of very low frequency (VLF) radio waves^1–4. Similar VLF-propagation effects are also produced by the localized dumping of electrons from the radiation belts after wave–particle interactions^5,6. Both nuclear explosions and particle precipitation events are of a transient nature, however, and no experimental study has yet been made to confirm these early theoretical predictions. With the development of a unique high frequency (HF) heating facility near Tromsø, Norway, the generation of movable controlled anomalies in the D-region has become possible. We describe here some initial observations, made in Norway, of the effect of such a movable D-region anomaly on the VLF signals received from the 12.1-kHz Omega transmitter at Aldra. The observations confirm the validity of earlier theoretical predictions.