Generation of Field‐Aligned Currents During Substorm Expansion: An Update

We investigated generation processes of field-aligned currents (FACs) that are abruptly intensified at the beginning substorm expansion phase by tracing a packet Alfvén wave backward in time from onset position ionosphere global magnetohydrodynamics (MHD) simulation. The region is found near-Earth plasma sheet, which (a) azimuthally moving pulls magnetic field line, and performs negative work against tension force to excite waves, (b) FACs generated requirement Ampère Faraday laws, (c) field-perpendicular current converted FACs. call this FAC dynamo. involved originates tail lobe region. When reconnection occurs accelerated earthward Lorentz force, decelerated pressure gradient followed force. flow deflected west east directions resulting excitation waves propagate along rest frame plasma. it arrives ionosphere, auroral electrojet starts developing begins. dynamo can be distinguished (J · E < 0, where J density electric field). suggest evolution understood terms development