Morphological aspects of a new type of counter electrojet event

The study describes the time and space morphologies of a rather new type of counter electrojet event on the basis of data from the excellent chain of magnetic and ionospheric observatories along the IndoRussian longitude sector. Abnormally large westward currents are observed during almost the whole of the daytime hours on a series of days. These events do not form any vortices in the current system and do not apparently seem to be associated with tidal e€ects or any solar magnetosphere events or geomagnetic disturbances. The existence of a westward electric ®eld over the equatorial ionosphere has been con®rmed by the absence of an equatorial type of sporadic E in the ionograms at Thumba precisely during the periods when DH at Trivandrum minus DH at Alibag is negative. The equatorial F region anomaly was also absent on the counter electrojet day. Such counter electrojet events during the northern winter months of low solar activity years are suggested to be the result of the modi®ed wind system in the ionosphere associated with stratospheric warming events.