A statistical study of magnetopause flux ropes and their substructure using Magnetospheric Multiscale mission (MMS)

During magnetic reconnection stored magnetic energy is released through the breaking and reconnecting of magnetic field lines, resulting in particle energisation. There have been many particle acceleration mechanisms proposed for magnetic reconnection, several of which involve flux ropes; helical magnetic field structures formed during the reconnection process. One mechanism suggests that contracting magnetic islands (the 2D analogue of flux ropes) can trap and accelerate electrons in a Fermi acceleration process, resulting in energetic electrons consistent with those associated with magnetic reconnection observations throughout the heliosphere. In previous work, we also demonstrated a mechanism for electron trapping and potential acceleration in 3D magnetic mirror structures on the edge of magnetopause flux ropes.

In this study, we present a statistical survey of magnetopause flux ropes investigated using the Magnetospheric Multiscale mission (MMS). MMS measures the thermal electron and ion 3D distributions at 30 msec and 150 msec time resolution, respectively, and at spacecraft separations down to a few kilometres, allowing a detailed study of the substructure of the flux ropes. We explore how the small-scale substructure is influenced by the large-scale properties of the flux ropes and the reconnection exhausts in which they are embedded, as well as the topology and connectivity of the field. The results illustrate the potential significance of flux ropes and their substructure for particle energisation in magnetopause reconnection.