THEMIS observations of extreme magnetopausemotion caused by a hot flow anomaly

摘要

On 30 October 2007, the five THEMIS spacecraft observed the cause andconsequence of extreme motion of the dawn flank magnetopause, displacing themagnetopause outward by at least 4.8 RE in 59 s, with flow speeds in the direction normalto the model magnetopause reaching 800 km/s. While the THEMIS A, C, D, and Eobservations allowed the determination of the velocity, size, and shape of a large bulgemoving tailward along the magnetopause at a speed of 355 km/s, THEMIS B observed thesignatures of a hot flow anomaly (HFA) upstream of the bow shock at the same time,indicating that the pressure perturbation generated by the HFA may be the source of thefast compression and expansion of the magnetosphere. The transient deformation of themagnetopause generated field-aligned currents and created traveling convection vorticeswhich were detected by ground magnetometers. This event demonstrates that kinetic(non-MHD) effects at the bow shock can have global consequences on the magnetosphere.