Seasonal variations in the incidence of auroral radio absorption events at very high latitude, and the influence of the magnetotail

A statistical analysis has been made of the incidence of auroral radio absorption events at South Pole, and of its dependence on basic geophysical parameters such as season, time of day, and magnetic activity level. It is found that at low and moderate levels of activity the incidence of events in the winter season is at least twice that in the summer. However, at high activity no events at all occurred during the local summer night, which appears to be explicable as the effect of the magnetotail and the consequent distortion of the magnetosphere when the southern polar region is tilted strongly towards the Sun. Previous results from even higher latitudes show the effect in an even more exaggerated form, in that both the day and night periods of absorption activity exhibit strong seasonal variations.