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A Significant Finding of New Morphological Type of Transpolar Arc: Nightside Distorted Transpolar Arc
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  • Motoharu Nowada,
  • Jun Yang,
  • Qiu-Gang Zong,
  • Quan-Qi Shi,
  • Yong-Fu Wang,
  • Hua-Yu Zhao,
  • Xu-Zhi Zhou
Motoharu Nowada
Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, People Republic of China

Corresponding Author:moto.nowada@sdu.edu.cn

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Jun Yang
Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, People Republic of China
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Qiu-Gang Zong
Institute of Space Physics and Applied Technology, School of Earth and Space Sciences, Peking University, People Republic of China
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Quan-Qi Shi
Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, People Republic of China
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Yong-Fu Wang
Institute of Space Physics and Applied Technology, School of Earth and Space Sciences, Peking University, People Republic of China
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Hua-Yu Zhao
Institute of Space Physics and Applied Technology, School of Earth and Space Sciences, Peking University, People Republic of China
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Xu-Zhi Zhou
Institute of Space Physics and Applied Technology, School of Earth and Space Sciences, Peking University, People Republic of China
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Abstract

Based on a large database of Wideband Imaging Camera (WIC), which is a part of Far Ultraviolet (FUV) instrument, onboard the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite during 5 years between 2000 and 2005, we found a new morphological type of transpolar arcs (TPAs), which are identified as “nightside distorted TPAs”. The nightside ends of the dawnside (duskside) TPAs got distorted toward pre- (post-) midnight sector; These TPAs look like the shape of an alphabetical letter of “J” or “L”. We identified 17 nightside distorted TPAs from our database. The 12 events out of 17 nightside distorted TPA events were the dawnside TPA with the nightside end distorted toward the pre-midnight sector (“J”-shaped TPA), and the TPAs in the duskside, whose nightside parts got distorted toward the post-midnight sector, were found in the remnant 5 events (“L”-shaped TPA). Statistically, the nightside distorted TPAs can dominantly be found under the northward Interplanetary Magnetic Field (IMF) conditions. Furthermore, when the IMF-By component pointed to the dawnward (duskward) direction, the “J” (“L”)-shaped TPAs were dominantly observed, suggesting that the relation between the IMF-Bz and By orientations, and the locations of the nightside distorted TPAs is consistent with that between the IMF conditions and regular TPA previously reported. We also followed the time sequence of the nightside distorted TPA evolution with the IMAGE FUV-WIC imager and additional Polar UVI data. In most cases, the “J” and “L”-shaped TPAs started to grow from the nightside main auroral oval, and protruded to the dayside region with being distorted. In this presentation, we will introduce several selected cases of the nightside distorted TPA among our database, and discuss why and how the nightside end of the TPA became distorted toward pre- or post-midnight sectors based on the in-situ satellite nightside plasma sheet observations and the electron drift velocity distribution calculated utilizing a simple electromagnetic field model in magnetotail, together with the auroral imager data.