Structure of large amplitude abrupt magnetic variations observed by the MAGSAT

• Main Authors: Toshihiko Iyemori, Akinari Nakagawa, Tatsuya Ikeda
• Format: Report
• Language: English
• Published: Data Analysis Center for Geomagnetism and Spacemagnetism, Faculty of Science, Kyoto University 1987
• Subjects: Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=2159; http://id.nii.ac.jp/1291/00002159/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=2159&item_no=1&attribute_id=18&file_no=1

The structure and occurrence characteristics of large amplitude abrupt magnetic variations that are frequently observed over the auroral oval are statistically analyzed using the high time resolution data obtained by the MAGSAT. A superposed epoch analysis shows a systematic difference in the structure between the upward and downward field-aligned currents, confirming that the abrupt variations are due to spatial structure of small-scale field-aligned current sheets. The estimated current density is very high (>90μA/m^2). The high density downward currents are canceled by adjacent strong upward currents, and the net current is upward or almost zero. On the other hand, a high density upward current does not necessarily accompany adjacent strong downward current, and the net current around the region is upward. The thickness of the current sheet is normally 0.5-1.0km or less, suggesting that the events are related to the rayed auroral arc elements. The occurrence frequency decreases rapidly as the amplitude of abrupt jump increases, and the dependence is describable by a simple power function, suggesting that the abrupt jumps are the events that distribute in the high density side trail of the small-scale field-aligned current density distribution.