Using MMS high‐resolution measurements, we present the first observation of fast electron jet (Ve ~2,000 km/s) at a dipolarization front (DF) in the magnetotail plasma sheet. This jet, with scale comparable to the DF thickness (~ 0.9 di), is primarily in the tangential plane to the DF current sheet and mainly undergoes the E × B drift motion; it contributes significantly to the current system at the DF, including a localized ring‐current that can modify the DF topology. Associated with this fast jet, we observed a persistent normal electric field, strong lower hybrid drift waves, and strong energy conversion at the DF. Such strong energy conversion is primarily attributed to the electron‐jet‐driven current (E ⋅ je ≈ 2 E ⋅ ji), rather than the ion current suggested in previous studies.

Whistler waves that can produce anomalous resistivity by affecting electrons' motion have been suggested as one of the mechanisms responsible for magnetic reconnection in the electron diffusion region (EDR). Such type of waves, however, has rarely been observed inside the EDR so far. In this study, we report such an observation by Magnetospheric Multiscale (MMS) mission. We find large‐amplitude whistler waves propagating away from the X line with a very small wave‐normal angle. These waves are probably generated by the perpendicular temperature anisotropy of the ~300 eV electrons inside the EDR, according to our analysis of dispersion relation and cyclotron resonance condition; they significantly affect the electron‐scale dynamics of magnetic reconnection and thus support previous simulations.

The electron rolling pin distribution, showing electron pitch angles primarily at 0°, 90°, and 180°, has recently been observed behind dipolarization fronts (DFs) and explained using an analytical model. However, the energy range of such distribution has been unknown so far, owing to the low‐resolution data in previous spacecraft missions. Here using the high‐resolution measurements of Magnetospheric Multiscale, we reveal the energy range of electron rolling pin distribution behind DFs for the first time. We find that such distribution appears only above 1.7 keV, falling well into the suprathermal energy range. Below 1.7 keV, electrons exhibit a Maxwell distribution, while above 1.7 keV, they exhibit a power law distribution. In addition, such distribution appears primarily in the growing phase of the flow and disappears quickly in the decaying phase. During the formation of the rolling pin distribution, electrons are gyrotropic. These findings have greatly improved our knowledge of electron dynamics around DFs.

Traditionally, the magnetotail flow burst outside the diffusion region is known to carry ions and electrons together (Vi = Ve), with the frozen‐in condition well satisfied (E + Ve × 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 (Ve ≠ Vi), with the electron speed 5 times larger than the ion speed. Such super‐Alfvenic electron jet, having scale of 10 di (ion inertial length) in XGSM direction, is associated with electron demagnetization (E + Ve × 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.

Magnetic reconnection is a fundamental energy conversion process where the magnetic field topology is reconfigured, dissipating efficiently magnetic energy into particle energy. In the magnetotail, magnetic reconnection results in mass, energy, and magnetic flux transport during substorms (