Observations of Short-Period Ion-Scale Current Sheet Flapping

TL;DR

This paper reports a short-period flapping event of a thin current sheet observed by MMS, revealing wave-like propagation, ion-scale dynamics, and associated lower hybrid waves in the Earth's magnetotail.

Contribution

It provides the first detailed observation of a 25-second ion-scale current sheet flapping event with analysis of its propagation and underlying plasma processes.

Findings

Wave-like structure propagates along current direction with ion velocity.

Wavelength scales with current sheet thickness, indicating drift-kink mode.

Decoupling of ion and electron motions suggests a thin current sheet.

Abstract

Kink-like flapping motions of current sheets are commonly observed in the magnetotail. Such oscillations have periods of a few minutes down to a few seconds and they propagate toward the flanks of the plasma sheet. Here, we report a short-period ($T\approx25$ s) flapping event of a thin current sheet observed by the Magnetospheric Multiscale (MMS) spacecraft in the dusk-side plasma sheet following a fast Earthward plasma flow. We characterize the flapping structure using the multi-spacecraft spatiotemporal derivative and timing methods, and we find that the wave-like structure is propagating along the average current direction with a phase velocity comparable to the ion velocity. We show that the wavelength of the oscillating current sheet scales with its thickness as expected for a drift-kink mode. The decoupling of the ion bulk motion from the electron bulk motion suggests that the current sheet is thin. We discuss the presence of the lower hybrid waves associated with gradients of density as a broadening process of the thin current sheet.