Electron-Driven Dissipation in a Tailward Flow Burst

Traditionally, the magnetotail flow burst outside the diffusion region is known to carry ions and electrons together (V_i = V_e), with the frozen-in condition well satisfied (E + V_e × B = 0). Such picture, however, may not be true, based on our analyses of the high-resolution MMS (Magnetospheric Multiscale mission) data. We find that inside the flow burst the electrons and ions can be decoupled (V_e ≠ V_i), with the electron speed 5 times larger than the ion speed. Such super-Alfvenic electron jet, having scale of 10 d_i (ion inertial length) in X_GSM direction, is associated with electron demagnetization (E + V_e × B ≠ 0), electron agyrotropy (crescent distribution), and O-line magnetic topology but not associated with the flow reversal and X-line topology; it can cause strong energy dissipation and electron heating. We quantitatively analyze the dissipation and find that it is primarily attributed to lower hybrid drift waves. These results emphasize the non-MHD (magnetohydrodynamics) behaviors of magnetotail flow bursts and the role of lower hybrid drift waves in dissipating energies.