The 2D evolution of the M-I responses to solar wind/foreshock transients based on the coordinated observation between THEMIS and ground-based ASI

Abstract

Dynamic pressure variations that are upstream from the magnetopause can interact with the coupled magnetospheric and ionospheric system, causing significant auroral responses, which indicates magnetospheric compressions, wave propagations and disturbances of current system. Recent studies have shown that not only large-scale solar wind structures but also locally-generated foreshock transients can be associated with strong dynamic pressure variations and further induce such auroral responses. However, how these auroral responses evolve in 2D perspective and how the corresponding current system and electron precipitation evolve in 2D perspective are still unclear. Thus, in our study, we used the coordinated observations between THEMIS probes and the ground-based all-sky images at South Pole to statistically investigate the 2D evolution of discrete and diffuse auroral responses to both solar wind structures and foreshock activities. The discrete auroral evolution shows that the dynamic pressure variations upstream from the magnetopause can induce upward field-aligned currents near the magnetopause in the magnetosphere. These currents can extend earthward and most of them extend duskward, causing the bifurcation of auroral oval. The diffuse auroral patterns reveal that in the ionosphere, the area with compression-related electron precipitations propagates poleward. The azimuthal motion of compression-related electron precipitations can be either dawnward or duskward, depending on the azimuthal propagation of the magnetospheric compressions. We further found that the location, size and associated dynamic pressure change of the upstream solar-wind or foreshock transients can modify the shape and 2D evolution of the corresponding auroral patterns.