Communication Research Laboratory/Communication Research Laboratory
Abstract
Long term variations of radio auroral activity are investigated from auroral radar data obtained at Syowa Station during 1978-1990. The diurnal variation of radio auroral activity shows a maximum in the post-midnight period with a small peak in the evening. Similar to the case of magnetic activity, the occurrence rate of radio aurora shows semi-annual variations with summer (December) and winter (June) time minimums. For post-midnight radio aurora, summer minimums are more pronounced than winter minimums. The magnetic activity controls the occurrence of evening time radio aurora more notably than post-midnight radio aurora. For the solar cycle variation, a double-peaked modulation is seen during 11-year sunspot cycle, with a major peak in the declining phase of the sunspot cycle and a secondary peak in the increasing phase
