Fade of transpolar arc and its relation to the intensification of the nightside auroral oval
| Autor: | OBARA, Takahiro |
|---|---|
| Jazyk: | japonština |
| Rok vydání: | 2021 |
| Zdroj: | 宇宙航空研究開発機構特別資料: 第17回「宇宙環境シンポジウム」講演論文集 = JAXA Special Publication: Proceedings of the 17th Spacecraft Environment Symposium. :7-12 |
| ISSN: | 2433-2232 |
| Popis: | 第17回宇宙環境シンポジウム (2020年10月7日-8日. 宇宙航空研究開発機構(JAXA)オンライン会議) The 17th Spacecraft Environment Symposium (October 7-8, 2020. Japan Aerospace Exploration Agency (JAXA), Online meeting) 北向き太陽風磁場の状態(IMF Bz>0)で、太陽風磁場の水平成分(IMF By)の極性が変わるとき、極冠域にトランスポーラ―アークと呼ばれるオーロラが出現する。このような状態で、太陽風磁場が南転した時、トランスポーラ―アークは消失を始め、しばらくすると、夜側オーロラオーバルが増光した。増光する場所は、北半球では、太陽風磁場の東西成分がマイナスになった時(IMF By0)は、トランスポーラ―アークの朝方側であった。この結果は、磁気圏対流MHDシミュレーションから予想される結果と一致する。 We have identified that night side oval intensification took place when the transpolar arc was fading. This is due to the switch of IMF Bz polarity from north to south. We have confirmed in the past that theta aurora appears in the polar cap region, corresponding to the IMF By polarity change (Type I) or long lasting strong IMF By (Type II) during northward IMF conditions. In the Type I case, the transpolar arc was detached from the morning (evening) side oval and moves dusk ward (dawn ward), corresponding to the IMF By polarity change from negative to positive (positive to negative). Movement of the transpolar arc is caused by the large supply of newly formed open field lines to the polar cap region, due to the change of the null point location. For the change of IMF By from negative to positive (positive to negative), accumulation of the magnetic flux occurs within the newly formed polar cap region in the dawn side (dusk side). When the IMF switched to the south, accumulation continues in the same side of the polar cap. Enhanced convention stores the energy and the stored energy at last releases, resulting in the intensification of the night side auroral oval. Location of the intensification with respect to the transpolar arc seems to depend on the IMF By polarity; i.e. dusk side for negative IMF By and dawn side for positive IMF By in the northern polar cap. For the Type II case, accumulation of open flux in the polar cap would enhance due to the switch of IMF Bz to the south, resulting in the intensification of the night side oval. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA2030009002 レポート番号: JAXA-SP-20-007 |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|