Fermi Acceleration of Electrons at Earth's Bow Shock Due To Current Sheet Interaction

We use the Magnetospheric Multiscale (MMS) mission to present a case study of electron acceleration at Earth's bow shock due to an interaction with a solar wind magnetic depression. The magnetic depression is identified as a reconnecting current sheet and is observed both at the bow shock, using MMS, and upstream of the shock at the Lagrange point 1 using the ACE, WIND, and DSCOVR spacecraft. The interaction with the current sheet and drop in magnetic field magnitude enables electrons to be accelerated from thermal energies (10–20 eV) up to suprathermal energies (1–5 keV) in a process producing a power‐law with a spectral index p = − 2.3 $p=-2.3$ close to that predicted by first order Fermi acceleration ( p = − 2 ) $(p=-2)$ . The observations are compared to a numerical model of Fermi acceleration considering two approaching magnetic mirrors and pitch angle scattering by whistler waves, and good agreement is shown. Thus, we add another piece to resolving the long‐standing electron injection problem.