The quiet-time equatorial electrojet and counter-electrojet.

Abstract

Using ground magnetometer data from several stations near the dip equator, the magnetically quiet-time characteristics of the daytime normal electrojet and the morning and afternoon counter-electrojets are established and illustrated. In particular, the solar cycle, seasonal, longitudinal and day-to-day variations of counter-electrojets as well as their dependence on lunar phase are studied. In order to investigate the influence of solar tidal winds in the production of counter-electrojets, the equatorial electric fields generated by such winds through the dynamo mechanism are calculated, using a numerical dynamo simulation model developed earlier at UCLA. From these calculations it is found that westward electric fields responsible for the afternoon counter-electrojets can be produced in the local summer solstice (when these events are most common) by a combination of the solar semidiurnal (2, 2) tide and the diurnal (1, -2) tide. An example from January 1964 is discussed to illustrate that afternoon counter-electrojet events occurring at all longitudes on the same day are likely to be associated with abnormalities in the global Sq or SR current system. It is suggested that the lunar semi-diurnal tide is a more important causative agent for the morning rather than the afternoon counter-electrojets.