On the simultaneous existence of Eastward and Westward flowing equatorial electrojet currents

Abstract

The counter-electrojet currents are evidenced by the disappearance of theq type of Es layer (Es-q) or the appearance of the blanketing type of Es (Es-b) at Kodaikanal, associated with the depression of the geomagnetic H field and the reveisal of ionospheric drift at Thumba. The necessary condition for such an event is not the decrease of the H field below the night level but that the difference of the H field between an equatorial and a non-equatorial station should decrease below its night level. The different kinds of association between the disappearance of Es-q and the depression in the H field are suggested due to superimposition over the Sq current system (at about 107 km) of a separate westward current system at a lower level (about 100 km). The source of the reversed current over the dip equator during the daytime hours is sought in the current system generated by the lunar tides or in various magnetospheric processes generating the polar substorms. Large day-to-day variations of the solar daily range of H at the equator independent of Sq variation at tropical latitudes are suggested to be due to superimposition at the equator of the two rather independent current systems.