The day-to-day variability in ionospheric electric fields and currents

The daily variations in ionospheric drift velocities are examined from incoherent scatter measurements at Millstone Hill. The data with ∑ Kp > 24 behave differently from those with low magnetic activity and basically follow the convection pattern but have large day-to-day variations. The influence of the magnetic conjugate point is discussed, and solar cycle variations are examined in conjunction with geomagnetic variations. Ionospheric currents calculated by using a semidiurnal neutral wind model are in good agreement with ground-based magnetograms for low magnetic activity, but the E region neutral wind model appears to be applicable only to this case.