Ariel 3 and 4 Studies of Power Line Harmonic Radiation

Abstract

Continuous on-board tape-recording of ELF/VLF signals on the Ariel 3 and 4 satellites has made it possible to study the world-wide distribution of PLHR and associated emissions above the ionosphere and their frequency of occurrence as a function of location, intensity, storm-time, season and solar cycle.

A particularly prominent zone of emission is obtained at VLF (3.2 kHz over N. America where frequent PLHR induced magnetospheric wave amplification up to 50 dB and typically 10 to 20 dB, is obtained at invariant latitudes 45 to 550° (2 < L < 3) centred on the electron slot. It appears that PLHR and associated emissions are responsible for pitch angle diffusion of energetic electrons (E ≥ 100 keV) at large pitch angles by first order gyroresonance and thereby contribute to the formation of the electron slot.

A marked lack of PLHR induced emission in winter is attributed to the inability of the waves to become entrapped in ducts. The dependence of signal intensity on storm-time is similarly attributed to duct formation and wave-trapping therein. One and two (or multi) hop emissions occur with about equal probability at 3.2 kHz; at 9.6 kHz one hop are predominant.

There is evidence of a possible association between PLHR emissions and thunderstorm activity at American longitudes.