Energy Conversion in the Dip Region Preceding Dipolarization Front

Dipolarization fronts (DFs), characterized by sharp increases in the northward magnetic field and usually preceded by magnetic dips, are suggested to play an important role in energy conversion and transport in the magnetotail. It has been documented that strong energy conversion typically develops right at the fronts. Here we present spacecraft observations of electron-scale energy conversion (EEC) developed inside the dip region ahead of a DF, by using high-cadence data from the Magnetospheric Multiscale Mission. The EEC, with magnitude comparable to that at the front, is primarily driven by ion current and electron-scale electric field. The electric field inside the dip is provided by electrostatic waves fed by lower hybrid drift instability, which experiences temporal decaying. Such decaying leads to nonhomogeneity of EEC along the dawn-dusk direction. These results, uncovering a new channel for DF-driven energy conversion, can provide important insights into understanding energy transport in the magnetotail.