Sequentially released tilted flux ropes in the Earth's magnetotail

Abstract

On 14 July 2011, the two ARTEMIS spacecraft observed a chain of flux ropes generated by reconnection in the Earth's magnetotail. The flux ropes are found to extend more than 90 ion inertial lengths out of the reconnection plane. We analyze six of these flux ropes by employing a novel combination of two-spacecraft-timing for their global orientation and Grad-Shafranov reconstruction (GSR) for their local orientation. We find that their diameter was ∼10 ion inertial lengths, temporal separations ∼100 ion gyroperiods, and that their speed increased from ∼30% to ∼70% of the Alfvén velocity. Given their temporal and spatial separations, we can infer that they were produced sequentially via a secondary instability. All of the flux ropes were tilted in the current sheet plane, suggesting that the secondary instability grew along the X-line in the direction of the electron current (-YGSM). The first five had a tilt between-14° and-26°. Based on the GSR axes their shape became increasingly complex over a period of ∼300 gyroperiods indicating kinking. The sixth event was again rather linear, and had a larger tilt (-38°), cross-section and core magnetic field; these changes are most likely related to a change in the boundary conditions. © 2014 IOP Publishing Ltd.