Day-to-day variability of the Sq geomagnetic field variation

It is noted that much apparent day-to-day variability in the H component of the S sub q variation in low and middle latitudes is not due to a variability in ionospheric currents, but arises from contamination by often unrecognized disturbance field variations associated with distant magnetospheric currents. Little if any day-to-day variability is seen in the shape, type, or phase of the pure S sub q variation. However, significant day-to-day variability exists in the daily range of S sub q, and this has a worldwide rather than a local cause. No conclusive evidence is seen for motion of the S sub q foci. It is noted that in low and middle latitudes the S sub q variation is in essence a daytime phenomenon.