Electrodynamics of the high‐latitude mesosphere

Abstract

The discovery of apparent large (V/m) electric fields within the mesosphere suggests that this region is more active electrically than originally suspected. High‐latitude observations have been particularly productive in developing new concepts regarding mesospheric electrodynamics. Several high‐latitude observations of large mesospheric fields have been made under both quiet and aurorally active conditions but always below heights where enhanced ionizing radiations could significantly penetrate. Two measurements from Andøya, Norway, have also produced an anticorrelation of horizontal electric field directions with neutral wind velocities, leading to the theoretical description of a newly defined mechanism for V/m electric field generation involving wind‐induced separation of charged aerosols. Evidence for mesospheric aerosols and winds exists at all latitudes but is most evident at high latitudes during the appearance of noctilucent and/or polar mesospheric clouds. New measurements show an influence of such clouds on electric fields mapping downward from the ionosphere, modifying the electric field in both magnitude and direction. Recent results also demonstrate that middle atmospheric electrical parameters can be used to track neutral air turbulence and wave structure at high latitudes, thereby providing a powerful tool for study of mesospheric neutral dynamics and its relationship to the electrodynamic system. This overview concentrates on the various subjects outlined above.