Dayside magnetospheric and ionospheric responses to a foreshock transient on 25 June 2008: 2. 2-D evolution based on dayside auroral imaging

The diffuse aurora brightening, which corresponded to a region a few Re size in geocentric solar magnetospheric Y in the equatorial plane, propagated duskward with an average speed of similar to 100km/s. Soon after the diffuse aurora brightened, discrete aurora also brightened and extended duskward, which was consistent with the motion of the foreshock transient as it swept through the magnetosheath while impacting the magnetopause.

Equivalent horizontal currents measured by magnetometers revealed a pair of field-aligned currents moving duskward consistent with motion of the discrete aurora patterns. We conclude that the high-resolution and two-dimensional observation of auroral responses by ground-based all-sky imager can help to estimate the evolution and propagation of upstream foreshock transients and their substantial impacts on the magnetosphere-ionosphere coupling system, including magnetospheric compression and currents in the ionosphere.