Electron Heating by Parallel Electric Fields in Magnetotail Reconnection

Abstract: We investigate electron heating by magnetic-field-aligned electric fields ($E_\parallel$) during anti-parallel magnetic reconnection in the Earth's magnetotail. Using a statistical sample of 140 reconnection outflows, we infer the acceleration potential associated with $E_\parallel$ from the shape of the electron velocity distribution functions. We show that heating by $E_\parallel$ in the reconnection outflow can reach up to ten times the inflow electron temperature. We demonstrate that the magnitude of the acceleration potential scales with the inflow Alfv\'en and electron thermal speeds to maintain quasi-neutrality in the reconnection region. Our results suggest that, as the inflow plasma parameter $\beta_{e\infty}$ increases, $E_\parallel$ becomes increasingly important to the ion-to-electron energy partition associated with magnetic reconnection.