Lower hybrid drift wave motion at a dayside magnetopause x-line with energy conversion dominated by a parallel electric field

Abstract

On December 4, 2017 at approximately 6:15:38 UTC, magnetospheric multiscale (MMS) encountered a reconnecting current sheet near the dayside magnetopause. MMS2 passed through the current sheet just sunward of the southward-moving x-line and observed the crescent-shaped electron velocity distributions associated with reconnection. Additionally, MMS2 observed anti-correlated oscillations in the Hall electric field EN and in the parallel electric field Eǁ at a frequency just below the lower hybrid (LH) frequency. These oscillations appear to be LH drift waves (also called corrugations), which have previously been observed along the dayside magnetopause but were not seen to cause the same kinds of oscillations in the electric field components as observed in this event. It appears that MMS2 periodically crosses a separatrix between the region where EN dominates and a different region where Eǁ dominates at the wave frequency likely due to the wave motion. We also observe energy conversion dominated by Eǁ and veǁ, mostly in the L-direction, in this region as opposed to the reconnection electric field EM and meandering electrons moving in the M-direction as is typically observed during reconnection near an x-line.