North-south Asymmetric Nightside Distorted Transpolar Arcs within A
Framework of Deformed Magnetosphere-Ionosphere Coupling: IMF-By
Dependence, Ionospheric Currents, and Magnetotail Reconnection
Alexander W Degeling
Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai
Author ProfileAn-Min Tian
Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai, Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai
Author ProfileAbstract
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 and Southern Hemispheres, 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 unravelled 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.