Aurora and the poleward edge of the main ionospheric trough

Abstract

The Chatanika incoherent scatter radar was used on fifteen days during the winter of 1971–1972 to provide data on ionospheric parameters in a meridional cross section of the auroral zone. On three of these days the aurora was quiet and conditions were sufficiently stable that variations during the observations could be ignored. These three cases, supported by the other less well-defined cases, provide the following results: (1) during one quiet period, the main ionospheric trough extended from 69° down to at least 61° geomagnetic latitude; (2) the poleward edge of the trough was a steep horizontal electron density gradient (essentially a wall of ionization) that is approximately field aligned, and its position appears to be determined not by the concurrent position of the visual aurora but by the most equatorward position of the visual aurora during the preceding hours; and (3) the maximum F region electron density in the space between the trough and the visual aurora occurs 1 to 2 deg of latitude equatorward of the aurora. These results are interpreted in terms of a qualitative model that invokes the equatorward and upward transport of aurorally produced ionization by collisional coupling with an equatorward neutral wind caused by auroral heating.