Variability of the equatorial electrojet: Its relations to the Sq current system and semidiurnal tides

Average diurnal and seasonal variations of the horizontal geomagnetic element ΔH are examined. The semiannual variation in equatorial electrojet strength is found to disappear in afternoon hours. This may be related to changes in the latitude of the Sq current system focus during the day. This in turn may be caused by a superposed semidiurnal tide and may also explain ΔH variations at stations near the focus.