THEMIS observations of the current sheet dynamics in response to the intrusion of the high‐velocity plasma flow into the near‐Earth magnetotail

Abstract

A small separation between Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes allows us to analyze a sudden activation in the near‐Earth current sheet (CS) at microscales. The start of the activation coincides with the appearance of an earthward plasma flow and dipolarization front (DF) at THEMIS location. The time sequence of observations of the fast plasma flow and the associated DF by three THEMIS probes denotes their dawnward displacement and the localization of the flow channel in the dawn‐dusk direction. The onset of kink perturbations of the CS was generated on the dawn side of the flow. These fluctuations also propagated dawnward and were followed by the CS thinning ( L ~ ρ i ) and by the development of tearing instability with transient appearance of a magnetic null point. The region of the unstable CS with a magnetic null point was localized in the X and, possibly, in the Y directions. The CS perturbations were most likely triggered by the intrusion of the fast flow into the ambient plasma in the course of the global dawnward displacement of the flow structure. Although no substorm onset was observed during the CS activation, a ground signature of a pseudobreakup was detected just after the excitement of the tearing mode in the near‐Earth tail. Probably the pseudobreakup was caused by a localized diversion of the current, which could result from the disruption of the cross‐tail current in a localized region of the near‐Earth CS. The intrusion of fast flow triggered kink and tearing modes in the CS