Global features of quiet time counterelectrojet observed by Ørsted

Abstract

[1] The present work investigates the reverse equatorial electrojet signature seen in the Ørsted satellite data, during magnetically quiet conditions. We found that whenever the satellite sees the reverse electrojet signature over the Indian region, it is always accompanied by the counter electrojet (CEJ) at Indian observatories, and therefore, the reverse electrojet signature at the satellite height can be considered a proxy for the CEJ observed on the ground. Then using satellite observations, global features of the CEJ phenomenon are obtained. The broad features of the phenomenon such as a seasonal variation of the CEJ occurrence frequency, and also its anticorrelation with the normal electrojet strength, are found to be in agreement with earlier ground-based studies. Satellite-based investigations have a distinct advantage over ground data for studying the global extent as well as the longitudinal variation of the CEJ occurrence. It is observed that in general, the longitudinal extent of the phenomenon is very narrow, often restricted to less than 25°. However, the present analysis suggests that strong westward currents generated at a given universal time can result in CEJ at wider longitudinal locations. The percentage of CEJ occurrence is found to be highest in the Brazilian sector, between 300°E and 330°E longitude. It is observed that the CEJ is prone to occur where the magnetic declination is large, highlighting the role of the geometry of the ambient geomagnetic field. The present study emphasizes that the CEJ occurs more favorably when and where the strength of the normal equatorial electrojet is weak.