Comprehensive Analysis of the Counter Equatorial Electrojet: Average Properties as Deduced From CHAMP Observations

Abstract

Ten years of geomagnetic field observations by the CHAMP satellite are used for a systematic investigation of the counter equatorial electrojet (CEJ). For the first time a comprehensive characterization of CEJ is presented. CEJs occur preferably during early morning, and their occurrence rate is down to 4% at noon. The CEJ occurrence rate shows a clear annual variation with a peak around July–August and a secondary peak in January. The late summer peak is related to the effect of meteor dust ablation. The CEJ amplitude is closely controlled by magnetic activity, showing a good correlation with the aP index. Nonmigrating solar tides are the main reason for longitudinal patterns of occurrence rate. The most prominent wavenumber 1 longitudinal structures during all seasons can be attributed to the tidal components SW3 and SPW1. The wavenumber 4 becomes largest during late summer-autumn season, which is related to the DE3 component. Also, the influence of lunar tides is evident in the CEJ occurrence rate. Strongest modulation of the CEJ by the semidiurnal lunar M2 tide is observed around January, which is responsible for the secondary CEJ occurrence peak in January. Both the solar and lunar tidal waves appear out of phase between CEJ and equatorial electrojet, implying that the same tidal mechanisms influence both current systems. Changes of solar wind conditions can also influence the CEJ. Immediately after a sudden increase of solar wind input CEJs are depressed, but about 3 hr after that event CEJs are strongly enhanced because of the disturbance wind dynamo.