Night-time reception of a solar radio event

It is stated that on the night of March 30 1976 anomalous high level radio bursts were recorded with a 48-channel polarised high resolution radio spectrograph operating at a frequency range of 20.85 to 23.20 MHz. The observation was made at Kiiminki, Finland, in the complete absence of interference of any kind. At the time a strong solar radio event was in progress, the associated bursts starting in the vicinity of 80 MHz. At the lowest recorded frequency of 25 MHz they matched well with the bursts here reported. Anomalous propagation of solar bursts had been observed previously. In the present case the bursts must have been guided from the sunlit hemisphere over the polar regions. On the night in question an auroral substorm and a strong blanketing sporadic E were observed, and a suitable duct may have existed between the ground and the Es layer. This is supported by the low attenuation of the bursts. The waves first penetrated the F2 layer, perhaps at a relatively high latitude, and then entered the duct beneath the Es layer, assuming that the latter extended far enough towards the sunlit hemisphere. (UK)