资源环境科技发展态势分析平台

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 of-fers 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 mechanism identified from multiple-instrument observations of unusually bright, multiple TPAs and simulations from a high-resolution three-dimensional (3D) global MagnetoHydroDynamics (MHD) model. The observations and simulations show an excellent agree-ment and reveal that these multiple TPAs are generated by pre-cipitating 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 supersonic 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 insight into the complex solar wind-magnetosphere-ionosphere coupling pro-cesses under a northward IMF condition, and it challenges existing paradigms of the dynamics of the Earth's magnetosphere.