North-south Asymmetric Nightside Distorted Transpolar Arcs within A Framework of Deformed Magnetosphere-Ionosphere Coupling : IMF-By Dependence, Ionospheric Currents, and Magnetotail Reconnection

Nowada, Motoharu and Song, Qiu-Gang and Hubert, Benoit and Shi, Quan-Qi and Wang, Yong-Fu and Yang, Jun and Grocott, Adrian and Degeling, Alexander W. and Tian, An-Min and Zhou, Xu-Zhi and Yue, Chao (2020) North-south Asymmetric Nightside Distorted Transpolar Arcs within A Framework of Deformed Magnetosphere-Ionosphere Coupling : IMF-By Dependence, Ionospheric Currents, and Magnetotail Reconnection. Journal of Geophysical Research: Space Physics, 125 (10): 2020JA0279. ISSN 2169-9402

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Abstract

The terrestrial magnetosphere is perpetually exposed to and significantly deformed by the interplanetary magnetic field (IMF) in the solar wind. This deformation is typically detected at discrete locations by space‐ and ground‐based observations. Earth's aurora, on the other hand, is a globally distributed phenomenon that may be used to elucidate magnetospheric deformations caused by IMF variations, as well as plasma supply from the deformed magnetotail to the high‐latitude atmosphere. We report the utilization of an auroral form known as the transpolar arc (TPA) to diagnose the plasma dynamics of the globally deformed magnetosphere. Nine TPAs examined in this study have two types of a newly identified morphology, which are designated as “J”‐ and “L”‐shaped TPAs from their shapes and are shown to have antisymmetric morphologies in the Northern Hemisphere and Southern Hemisphere, depending on the IMF polarity. The TPA‐associated ionospheric current profiles suggest that electric currents flowing along the magnetic field lines (field‐aligned currents [FACs]), connecting the magnetotail and the ionosphere, may be related to the “J”‐ and “L”‐shaped TPA formations. The FACs can be generated by velocity shear between fast plasma flows associated with nightside magnetic reconnection and slower background magnetotail plasma flows. Complex large‐scale TPA FAC structures, previously unraveled by an magnetohydrodynamic (MHD) simulation, cannot be elucidated by our observations. However, our interpretation of TPA features in a global context facilitates the usage of TPA as a diagnostic tool to effectively remote sense globally deformed terrestrial and planetary magnetospheric processes in response to the IMF and solar wind plasma conditions.