Response of equatorial electrojet during the super geomagnetic storm of April 2000

A major geomagnetic storm associated with coronal mass ejection (CME) occurred with sudden commencement at 1636 hrs UT on 6 April 2000 and a minimum Sym/H index of -300 nT at 0000 hrs UT on 7 April 2000. The event is unique with IMF Bz remaining southward from around 1630 hrs UT till almost midnight. The event is studied from data at a chain of ground magnetometers in the Indian and Pacific longitude sectors and other low latitude stations. The amplitude of SC (H) at low latitude stations was highest at Huancayo (around local mid-day) with a value of about 150 nT and about 45 nT at Tirunelveli in the Indian sector (nighttime). The amplitude of SC in H in the night side Indian sector showed an increase with latitude with a value of about 45 nT near dip equator and increased to about 85 nT near Sq focus. Counter electrojet was seen from 0400 to 1100 hrs UT (maximum value of -70 nT) in the Indian sector and the ionograms at Thumba showed disappearance of Es-q at 1130 hrs LT (0630 hrs UT) and its reappearance at 1630 hrs LT (1130 hrs UT). The long duration counter electrojet in the Indian sector is likely due to disturbance dynamo fields. Strong counter electrojet event from 0000 to 0300 hrs UT (maximum value of about -300 nT) in the far-east sector is probably due to prompt penetration electric field (over shielding) associated with the sudden northward turning of IMF Bz around midnight.

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