Characteristics of small-scale magnetic fluctuations over the high-latitude ionosphere

• Main Authors: Toshihiko Iyemori, Tatsuya Ikeda, Akinari Nakagawa
• Format: Report
• Language: English
• Published: Data Analysis Center for Geomagnetism and Spacemagnetism, Faculty of Science, Kyoto University 1986
• Subjects: Birkeland; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1995; http://id.nii.ac.jp/1291/00001995/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1995&item_no=1&attribute_id=18&file_no=1

The global amplitude distributions of the small-scale (1<L<35km) or short-time scale (0.12<T<5s) magnetic fluctuations over the high-latitude ionosphere are obtained for various geomagnetic, seasonal and IMF conditions using the MAGSAT data and are compared with the large-scale Birkeland currents. On the dayside, the maximum of the amplitude distribution appears near the poleward edge of the large-scale Birkeland current region-1 or at the latitude poleward of it. The amplitude strongly depends on the ionospheric conductivity and varies about factor three or more even in the same conditions of the geomagnetic activity, suggesting that the fluctuations are generated mainly by small-scale Birkeland currents rather than by Alfven waves. The IMF-By causes the dawn-dusk asymmetry of the amplitude and the IMF-Bz controls the latitudinal distribution of the fluctuations. On the night-side, the amplitude is controlled mainly by the geomagnetic activity, and the active region statistically corresponds to the large scale Birkeland current regions. However, the correlation between the amplitude and the large-scale Birkeland current density is not necessarily good. On both sides, the latitude of the maximum amplitude roughly correspond to that of the large-scale magnetospheric convection reversal, suggesting that the small-scale Birkeland currents originate from the turbulence generated in the strong convection shear regions.