Suprathermal Ions Observed Inside a Magnetic Flux Rope in the Earth's Magnetotail

Abstract

AbstractSuprathermal ions have not been observed inside magnetic flux ropes, although energetic electrons have been extensively detected and were thought to be accelerated inside magnetic flux ropes. In this paper, we present the first observation of the suprathermal ions inside a magnetic flux rope in the Earth's magnetotail with a spatial‐scale of tens of ion inertial length. This flux rope was propagating earthward, and its leading part was substantially compressed while its trailing part was significantly stretched. The suprathermal ions can be detected inside the whole flux rope and displayed distinct pitch angle distributions between its leading and trailing parts. In the leading part, the ion fluxes were enhanced primarily in the direction perpendicular to the magnetic field in the all measured energy range, while the ion fluxes increased in the parallel and antiparallel directions in the trailing parts. A large flow vortex was observed immediately behind the flux rope, consistent with Kármán vortex street. The observation suggested that a flux rope even with a large scale can still be highly dynamic, and the charged particles can be significantly accelerated during the flux rope evolution in magnetic reconnection.