Relationship between large horizontal electric fields and auroral arc elements

Abstract

High time resolution optical measurements in the magnetic zenith are compared with European Incoherent Scatter (EISCAT) field‐aligned measurements of electron density at 0.2‐s resolution and with horizontal electric field measurements made at 278 km with resolution of 9 s. In one event, 20 min after a spectacular auroral breakup, a system of narrow and active arc elements moved southward into the magnetic zenith, where it remained for several minutes. During a 30‐s interval of activity in a narrow arc element very close to the radar beam, the electric field vectors at 3‐s resolution were found to be extremely large (up to 400 mV m −1 ) and to point toward the bright optical features in the arc, which moved along its length. It is proposed that the large electric fields are short‐lived and are directly associated with the particle precipitation that causes the bright features in auroral arc elements.