Nonlocal Acceleration of Electrons During Substorms

Magnetic reconnection in a magnetized plasma represents a change in the topology of magnetic fields and is associated with a concomitant energization of charged particles that results from a conversion of magnetic energy into particle energy. In Earth’s magnetosphere this process is associated with the entry of solar wind into the magnetosphere and with the initiation of auroral substorms. Using data from the THEMIS mission together with global and test particle simulations, we demonstrate that electrons are energized in two distinct regions: A low energy population (up to a few keV) appears to arise in the diffusion region where particles are demagnetized and the magnetic topology changes. A high energy component that is energized by betatron acceleration arises within dipolarization fronts as they sweep toward the inner magnetosphere far from the diffusion region. This study concludes that particle energization is not associated solely with the conversion of magnetic to kinetic energy but, at least in the magnetosphere, also arises in conjunction with macroscopic flows.