Electron‐Scale Measurements of Dipolarization Front

Abstract

Dipolarization front (DF)—a sharp boundary with scale of ion inertial length (c/ωpi) in the Earth's magnetotail—can also have fine structures at electron scale (c/ωpe). Such electron‐scale structures, determining the local energy conversion, have not been revealed by multispacecraft observations so far, due to the large separation of spacecraft in previous studies. Here we report the first electron‐scale multispacecraft measurements of DF, using data from the recent Magnetospheric Multiscale mission. We find strong parallel currents only in the high‐density side of the DF but strong perpendicular currents across the whole DF. We find no parallel electric fields during the DF interval. Although DF is primarily an energy‐load region (E·J > 0), the electron‐scale currents could lead to a localized energy generation (E·J < 0). Such features are different from those reported in previous multispacecraft studies, where the currents, electric fields, and energy conversion are uniform across the DF; they also shed lights on the study of substorm current wedge, which is crucial in the magnetosphere‐ionosphere coupling.

Electron‐Driven Dissipation in a Tailward Flow Burst

“…As can be seen, inside the electron jet, both energy conversion (see red line in Figure g) and energy dissipation (see red line in Figure h) were primarily negative, indicating an energy transfer from particles to electromagnetic field. The magnitude of maximum energy dissipation reached 2 nW/m 3 (Figure h), much larger than that at dipolarization fronts (Angelopoulos et al, ; Huang et al, ; Liu, Fu, Vaivads, et al, ; Liu, Fu, Xu, et al, ; Yang et al, ). Since the current was primarily from electrons, the energy dissipation in this event was driven by electrons.…”

Ion‐Beam‐Driven Intense Electrostatic Solitary Waves in Reconnection Jet

“…The intense electric fields at the JF, with both N and M components dominant (Figure c), exhibit spiky features. Such features are due to the ripples generated by lower hybrid drift instability, which is driven by density gradient at the front (Liu, Fu, Xu , et al, ; Pan et al, ). Sharp changes in the electron and ion distributions are observed at the JF crossing.…”

“…Now we focus on the flux pileup region behind the JF, where large‐amplitude E M and E L components are observed. The persistent E M ~ V N × B L is the motional electric field arising from the enhanced magnetic field strength and high‐speed flow (Fu et al, ; Liu, Fu, Xu , et al, ). The short‐period intense E L ~ E ∥ is the parallel electric field as the angle between the L direction and the local B is less than 3°.…”

Energy Range of Electron Rolling Pin Distribution Behind Dipolarization Front

“…The dipolarization front (DF), characterized by a sharp increase of magnetic field Bz (Fu et al, ; Liu, Fu, Xu, et al, ; Nakamura et al, ; Runov et al, ) and typically preceded by a small Bz dip structure (Schmid et al, ; Yao et al, ), is frequently observed in the Earth's magnetotail associated with bursty bulk flows (Fu et al, ; Liu et al, ; Schmid et al, ). It plays an important role in the energy conversion (Angelopoulos et al, ; Huang et al, ; Liu, Fu, Vaivads, et al, ), particle acceleration (Fu et al, ; Zhou et al, ), and transport of mass and magnetic fluxes (Liu et al, ; Nakamura et al, ).…”