EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Multiple transpolar auroral arcs reveal new insight about coupling processes in the Earth’s magnetotail

Qing-He Zhang1, Yong-Liang Zhang2, Chi Wang3, Michael Lockwood4, Hui-Gen Yang5, Bin-Bin Tang3, Zan-Yang Xing1, Kjellmar Oksavik6,10, Larry R. Lyons7, Yu-Zhang Ma1, Qiu-Gang Zong8, Jøran Idar Moen10,9, and Li-Dong Xia1
Qing-He Zhang et al.
  • 1Institute of Space Sciences, Shandong University, Weihai, Shandong, 264209, China (
  • 2The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, USA
  • 3Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, China.
  • 4Department of Meteorology, University of Reading, Earley Gate, Post Office Box 243, RG6 6BB, UK.
  • 5Polar Research Institute of China, Shanghai, China
  • 6Birkeland Centre for Space Science, Department of Physics and Technology, University of Bergen, Bergen, Norway
  • 7Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, California, USA
  • 8School of Earth and Space Sciences, Peking University, Beijing, China
  • 9Department of Physics, University of Oslo, Blindern, Oslo, Norway
  • 10The University Centre in Svalbard, Longyearbyen, Norway

A distinct class of aurora, called transpolar auroral arc (TPA) (in some cases called “theta” aurora), appears in the extremely high latitude ionosphere of the Earth when interplanetary magnetic field (IMF) is northward. The formation and evolution of TPA offers clues about processes transferring energy and momentum from the solar wind to the magnetosphere and ionosphere during a northward IMF. However, their formation mechanisms remain poorly understood and controversial. We report a new mechanism identified from multiple-instrument observations of unusually bright, multiple TPAs and simulations from a high-resolution three-dimensional global MagnetoHydroDynamics (MHD) model. The observations and simulations show an excellent agreement and reveal that these multiple TPAs are generated by precipitating energetic magnetospheric electrons within field-aligned current (FAC) sheets. These FAC sheets are generated by multiple flow shear sheets in both the magnetospheric boundary produced by Kelvin-Helmholtz instability between super-sonic solar wind flow and magnetosphere plasma, and the plasma sheet generated by the interactions between the enhanced earthward plasma flows from the distant tail (less than -100 RE) and the enhanced tailward flows from the near tail (about -20 RE). The study offers a new insight into the complex solar wind-magnetosphere-ionosphere coupling processes under a northward IMF condition, and it challenges existing paradigms of the dynamics of the Earth’s magnetosphere.

How to cite: Zhang, Q.-H., Zhang, Y.-L., Wang, C., Lockwood, M., Yang, H.-G., Tang, B.-B., Xing, Z.-Y., Oksavik, K., Lyons, L. R., Ma, Y.-Z., Zong, Q.-G., Moen, J. I., and Xia, L.-D.: Multiple transpolar auroral arcs reveal new insight about coupling processes in the Earth’s magnetotail, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3780,, 2021.