[P-EM11] Dynamics of Magnetosphere and Ionosphere

[PEM11-07] Nightside Distorted Transpolar Arcs and Their Possible Formation Process Model

*野和田 基晴¹、扬 俊¹、ヒューベルト ベノワ²、宗 秋刚³、史 全岐¹、王 永福³、周 煦之³、赵 华宇³ (1.山東大学 威海校 空間科学与物理学学院 空間科学研究院 空間天気物理与探計測研究中心 、2.リージュ大学 宇宙科学技術天文研究所、3.北京大学 地球与空間科学学院 空間物理与応用技術研究所)

キーワード：夜側に歪みを持つトランスポーラーアーク: “J”- and “L” 型トランスポーラーアーク、夜側磁気圏磁気リコネクション、リコネクションポイントの磁気圏尾部への直線的或いは歪曲的後退、動的平衡状態、磁気圏対流

Transpolar Arc (TPA) is an important auroral phenomenon when considering how the energy stored in magnetotail is transported to ionosphere via magnetic reconnection under the northward interplanetary magnetic field. Magnetotail reconnection is considered to play a crucial role in TPA formation. Reconnection X-points are expected to retreat tailward as TPA grows from nightside auroral oval to the dayside. Usually, they straightforwardly retreat tailward, and reconnection-formed TPA morphology is straight-bar shape. However, we wonder how the TPA shape would be expected when traces of the tailward X-point retreats were not straightforward. The Wideband Imaging Camera (WIC), which is a part of Far Ultraviolet (FUV) instrument, onboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite detected an interesting type of TPAs, which are identified as “nightside distorted TPAs”. Their main bar-shaped parts were located at the dawn or dusk sides, and the nightside ends of them got distorted toward pre- or post-midnight sectors. Because these TPAs look like the shape of an alphabetical letter of “J” or “L”, we distinguished the nightside distorted TPAs from “J”- and “L”-shaped TPAs. We followed the time sequence of the evolutions of several nightside distorted TPAs with the IMAGE FUV-WIC imager data. In most cases, the “J” and “L”-shaped TPAs started to grow from the nightside main auroral oval, and protruded to the dayside auroral oval via the experience of distortion, suggesting that magnetotail magnetic reconnection was closely be related with the formation of the nightside distorted TPAs. In this study, we have proposed a model to explain the nightside distorted TPA formation, in order to discuss that TPAs with their nightside ends distorted toward pre- or post-midnight were formed through how physical process. Furthermore, we have tried to verify whether or not our model proposed is appropriate to adequately explain formation process of nightside distorted TPA based on the global MHD simulation using the BATS-R-US codes.