STUDIES OF THE E-REGION NEUTRAL WIND IN THE QUIET AURORAL IONOSPHERE

Quiet time auroral E region neutral wind data obtained by European Incoherent Scatter Radar (EISCAT) have been analyzed in order to establish the background mean neutral velocities as well as tidal influence on the wind. There is a rather strong and persistent mean eastward wind present in all seasons in the E region below 120 km. It is strongest in summer (approximately 60 m s-1), weak in fall and spring, and weaker in winter (approximately 20 m s-1). The zonal wind is westward above 120 km, in general stronger in winter (approximately 70 m s-1) and weaker in the other seasons (approximately 30 m s-1). The northward mean wind is rather small (approximately 10 m s-1). It is shifted gradually from being mainly southward in winter to becoming northward in summer. The mean vertical velocity is of the order of 5 m s-1 in the auroral E region. The amplitude of the diurnal tides of the vertical component have broad minima in the height region between 90 and 120 km. The horizontal diurnal tide is dominant in the upper E region, while the semidiurnal tide has a maximum at 110 km, in particular in the eastward component. The 8- and 6-hour tides are rather constant in amplitude by height. The results obtained are in good agreement with other results published on the basis of incoherent scatter radar measurements. The comparison with theoretical models underlines the need for more modeling of the auroral E region neutral tides including the ionized plasma as well as electric fields and mean background winds. Theoretical studies of the vertical motion with respect to the influence of tides are especially lacking in this important region.