Control factor of solar cycle variation of auroral kilometric radiation

概要

論文の詳細を見る
Solar cycle variations of auroral kilometric radiation (AKR) observed by the Akebono satellite have been compared with the variations of F10.7 and solar wind dynamic pressure. F10.7 and solar wind dynamic pressure show different solar cycle variations: F10.7 increases during solar maximum and decreases during solar minimum. Solar wind dynamic pressure suddenly increases in the declining phase of solar activity and gradually decreases. The pressure minimum occurs during solar maximum. Statistical analysis of the Akebono data has shown that AKR occurrence minimum occurs during solar maximum, however AKR occurrence maximum coincides not with solar wind dynamic pressure peak but with F10.7 minimum. Up-flowing ion (UFI) events and ambient plasma density, which are associated with generation conditions of AKR, also show similar behavior. They are dependent not on solar wind dynamic pressure but on F10.7. These results suggest the anti-correlation between discrete aurora and solar activities, which has been never recognized through the studies on secular variations of auroral phenomena mainly based on old auroral records obtained in mid-latitude regions.