V.L.F. observations on Ariel III: a preliminary report

The very-low-frequency receiver carried by Ariel HI makes synoptic studies at 3-2, 9-6 and 16 kHz of the world-wide distribution and occurrence of natural v.l.f. phenomena such as whistlers, chorus and hiss and also determines the configuration of the wave-field above the ionosphere due to the GBR (Rugby) transmission at 16 kHz. At these three frequencies the peak, mean and minimum signals are measured in each 28 second period (~2°) around the orbit. This report is based on a preliminary analysis of 36 orbits (quick-look data). Zones of emission, mainly hiss, are present on every orbit. They occur at both high and medium latitudes and may often extend over 20° in invariant latitude and down to within 20° of the geomagnetic equator. Whistlers, at medium latitudes, are usually easily identified by the large peak, very low mean and zero minimum signal levels. The,signal amplitudes often vary rather smoothly along the orbit and the pattern of signal amplitude may be repeated on different orbits following the same sub-satellite path. The geomagnetic field and the D-region are the main factors determining the configuration and intensity of the GBR (Rugby) 16 kHz wave-field above the ionosphere. Signals were identified at locations as remote as the Antipodes and the North Pacific.