Geomagnetic cutoff effect as an evidence for the corpuscular nature of anomalous VLF disturbances

Abstract

The effect of geomagnetic cutoff with respect to the primary ionizing flux, which caused anomalous VLF disturbances on a completely auroral radio path with a moderate length (∼900 km), has been proved. Abnormality manifested itself in a qualitative similarity of amplitude and phase variations at all three working frequencies of this radio path. This should not be observed if the contribution of the second ionospheric ray to the received field is substantial. This similarity is still the only signature of ultrarelativistic electron precipitation. The VLF data for the auroral and long partially auroral radio paths with a common receiver point (10–16 kHz) in the auroral zone have been qualitatively compared in order to prove the geomagnetic cutoff effect. The experimental database on disturbances occupies six years in the vicinity of the solar activity minimum (1982–1987). The manifestation of the magnetic cutoff in the above experimental data indicates that the primary ionizing flux is of the corpuscular nature. This flux generates X-ray bremsstrahlung, which produces the ionized sporadic DS layer in the middle auroral atmosphere.