V.l.f. observations on Ariel III

Abstract

The v. l. f. experiment on Ariel III is designed to make a synoptic study of the worldwide distribution and occurrence of v. l. f. electromagnetic wavefields above the ionosphere using a multi-channel receiver with a loop aerial. This report is based on a preliminary examination of data obtained during some 200 satellite revolutions. It has been found convenient to divide the observed phenomena into four main classes. ( a ) Man made transmissions . These are signals transmitted at 16 kHz from GBR (Rugby), U. K. and at 15⋅5 kHz from NWC (Australia). ( b ) Medium and low latitude emissions . These usually have a well-defined high latitude boundary—probably the plasma pause. ( c ) High latitude ‘hiss' . This well-defined zone of broad band noise occurs at invariant latitudes, Ʌ, greater than 60° ( L = 4) and is observed on the majority of revolutions. It is probably associated with the inner zone of soft electron (few keV) precipitation located outside the trapping boundary. ( d ) Thunderstorm emissions . The sferic impulses of large signal amplitude, generated in lightning discharges, are a powerful probe for the study of D-region phenomena and of geomagnetic field-alined structure in the ionosphere and magnetosphere. The occurrence and behaviour of these phenomena are discussed in relation to the structure of the magnetosphere and to magnetic storm effects. The equatorial arch of enhanced ionization is also found to have a marked effect on the v. l. f. wavefields.