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タイトル: | Substorm simulation: Insight into the mechanisms of initial brightening |
著者: | Ebihara, Y. Tanaka, T. |
著者名の別形: | 海老原, 祐輔 |
キーワード: | substorm expansion onset initial brightening MHD simulation field-aligned current magnetosphere-ionosphere coupling |
発行日: | Sep-2015 |
出版者: | American Geophysical Union |
誌名: | Journal of Geophysical Research: Space Physics |
巻: | 120 |
号: | 9 |
開始ページ: | 7270 |
終了ページ: | 7288 |
抄録: | Initial brightening of the aurora is an optical manifestation of the beginning of a substorm expansion and is accompanied by large-amplitude upward field-aligned currents (FACs). Based on global magnetohydrodynamic simulation, we suggest the possible generation mechanism of the upward FAC that may manifest the initial brightening. (1) A formation of the near-Earth neutral line (NENL) releases the tension force that accelerates plasma earthward. (2) The earthward (perpendicular) flow is converted to a field-aligned flow when flow braking takes place. (3) A high-pressure region propagates earthward along a field line. (4) The off-equatorial high-pressure region pulls in and discharges ambient plasma, which generates a flow vorticity around it. (5) Region 1-sense FAC is generated in the upper part of the off-equatorial high-pressure region. (6) The upward FAC is connected with the ionosphere in the center of the Harang discontinuity, causing the initial brightening. Additional dynamo is generated in the near-Earth region, which transmits electromagnetic energy. Upward FAC that manifests the initial brightening seems to be necessarily originated in the near-Earth off-equatorial region where the magnitude of the perpendicular (diamagnetic) current is relatively small in comparison with that of the FAC. Near the equatorial plane, the perpendicular current is comparable to or larger than FAC so that a current line is diverted from a magnetic field line and that the FAC generated near the equatorial plane is not necessarily connected with the ionosphere. The proposed mechanism occurs regardless of the location of the NENL and may explain some of auroral forms. |
著作権等: | ©2015. The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. |
URI: | http://hdl.handle.net/2433/203274 |
DOI(出版社版): | 10.1002/2015JA021516 |
出現コレクション: | 学術雑誌掲載論文等 |
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