Subion-Scale Flux Rope Nested Inside Ion-Scale Flux Rope in Earth's Magnetotail

Abstract

Magnetic flux ropes (MFRs)—transient magnetic structures widely observed in Earth's magnetosphere—play crucial roles in particle acceleration and energy dissipation. MFRs above ion scale have been well studied, while MFRs at subion scales and their coupling with larger-scale ropes still remains not well understood. In this paper, we present the first observation of a subion-scale MFR nested in an ion-scale MFR, using high-resolution data from the magnetospheric multiscale (MMS) mission. We find that the subion-scale MFR hosts more intense plasma activity than the ion-scale MFR, including distinct electron agyrotropy and strong electromagnetic turbulence. In addition, axis of the subion-scale MFR is oblique to that of the ion-scale MFR, indicating that their generation may be ascribed to 3D magnetic reconnection. Observations of such cross-scale structure may shed new lights into understanding energy cascade in space plasmas.