Tests of electrodynamic consistency from daytime ionospheric drift observations

Abstract

Observations of the daytime horizontal ion drift velocity in the ionospheric E and F regions by the incoherent scatter radar at Millstone Hill (42.6°N) during quiet geomagnetic conditions reveal the presence of a clockwise rotation of the drift direction with a semidiurnal period and a lag in the azimuth of the E region drift of 50°–60° behind the F region drift. The F region horizontal ion drifts result from the presence of ionospheric polarization electric fields, while at E region heights the ions are additionally driven by neutral winds. By using the electric fields determined from the F region drifts it is possible to derive information on the neutral winds from the E region drifts. The winds so obtained are found to be in good agreement with appropriately height averaged tidal winds in the lower thermosphere corresponding primarily to the (2, 4) propagating mode. This mode has been identified independently from temperature measurements at Millstone Hill. Conversely, calculations for the E region ion drift as a consequence of the combination of the (2, 4) tidal winds and the observed electric fields are shown to reproduce all features of the observations. Finally, the electric currents in the dynamo region have been computed from these experimental data and are shown to produce a magnetic variation at the ground that is similar to the observed average Sq variation at mid-latitudes, indicating the overall consistency of our observations.