Electron Heating Within the Earth's Bow Shock

High-temporal-resolution measurements of electron velocity distributions, f(→v), have been obtained for many transits through the Earth's bow shock. Within all oblique shocks studied, the maximum of f(→v) is offset with respect to the ion rest frame parallel to →B and directed downstream. These observations indicate that electron thermalization within the bow shock consists first of a downstream acceleration parallel to →B by the macroscopic shock electric field, followed by beam-driven plasma instabilities.