Dayside and nightside segments of a polar arc: The particle characteristics

Abstract

Using multiple satellites and a ground‐based radar network, the physical characteristics of a polar arc and its evolution are investigated under quiet solar wind conditions. The average electron energy is higher at the near‐midnight segment than at the sunward extension of the polar arc. Both polar arc segments are positioned primarily on closed magnetic field lines. The convection reversal boundary in the fitted convection pattern was located close to the transition region in the average electron energy seen by the satellites. The topside plasma density at an altitude of 680 km is clearly enhanced around the polar arc, although the enhancement boundary does not coincide precisely with that of the precipitation. The temporal sequence of auroral images suggests that the polar arcs emerged from a double oval structure. This suggestion is supported by the observed physical characteristics of the polar arc, which are quite similar to those of double oval structures that have been reported previously.