Deformations of the geomagnetic tail during flapping observed by MMS

Abstract:

Flapping of the geomagnetic tail is a common phenomenon, consisting of quasi-periodic North-South oscillations
of the tail current sheet. The geometry of these perturbations has thus far largely only been inferred from
single-point observations of the changing magnetic field. The combination of high-resolution magnetometers on
four observatories in a close, regular tetrahedron formation allows the Magnetospheric MultiScale mission (MMS)
to observe the geometry of the geospatial magnetic field in unprecedented detail. We use these unique facilities
of MMS to analyze and compare the geometry of the flapping tail neutral sheet in three categories:
a) The undulating quiet neutral sheet, b) A tilted flapping current sheet, and c) A flapping, thin current sheet
supporting reconnection. We discuss the relation between these categories in terms of current sheet thickness
and the increasing complexity of its magnetic structure across an entire Dawn-Dusk MMS tail season.
The propagation and velocity of these traveling disturbances both along and across the tail is also discussed.