Observations of Energy Conversion Caused by Magnetic Reconnection at a Dipolarization Front.

Dipolarization fronts (DFs) are widely believed to host energy conversion processes. However, which mechanism is responsible for the energy conversion is still obscure. Using data from the Magnetospheric Multiscale mission, a current sheet is observed at a DF. This current sheet is caused by interchange instability bending the edge of the DF. Inside the current sheet, Hall electromagnetic field, super Alfvénic electron jets, demagnetization of ions and electrons, strong energy conversion, and steady ion flow and temperature are observed, indicating an electron‐only reconnection at the DF. The duskward plasma flow, which may be deflected by the DF, compresses the bent edges of the DF. As a result, the width of the current sheet between two adjacent bent edges of the DF reduces, and then reconnection begins. Our observations give direct evidence that magnetic reconnection results in energy conversion at a DF. Plain Language Summary: Magnetic reconnection is an explosive phenomenon in space, which can rapidly convert energy from magnetic field to particles. Dipolarization fronts are essential carriers of mass and energy from the magnetotail to the Earth. Strong energy conversion, considered to be even more significant than magnetic reconnection, is usually observed at dipolarization fronts. However, the specific mechanism responsible for the energy conversion at a dipolarization front is elusive. Using data from the Magnetospheric Multiscale mission, we present direct evidence of magnetic reconnection at a dipolarization front, leading to strong energy conversion. The reconnection occurs in the current sheet at the dipolarization front. The duskward diverted flow compresses the bent dipolarization front induced by interchange instability, resulting in reconnection. Key Points: A current sheet with strong energy conversion is found at a DFThe strong energy conversion at this DF is mainly caused by the magnetic reconnectionThe duskward diverted flow compresses the bent DF caused by interchange instability, leading to the reconnection [ABSTRACT FROM AUTHOR]