Electron Heating by Parallel Electric Fields in Magnetotail Reconnection

We investigate electron heating by magnetic-field-aligned electric fields (E_{∥}) during antiparallel magnetic reconnection in the Earth's magnetotail. Using a statistical sample of 140 reconnection outflows, we infer the acceleration potential associated with E_{∥} from the shape of the electron velocity distribution functions. We show that heating by E_{∥} in the reconnection outflow can reach up to 10 times the inflow electron temperature. We demonstrate that the magnitude of the acceleration potential scales with the inflow Alfvén and electron thermal speeds to maintain quasineutrality in the reconnection region. Our results suggest that, as the inflow plasma parameter β_{e∞} increases, E_{∥} becomes increasingly important to the ion-to-electron energy partition associated with magnetic reconnection.