K. G. Simi
University of Kerala
India
Title: Evidence of successive under shielding and overshielding event during a geomagnetic storm and subsequent changes in the electrodynamics of equatorial upper atmosphere
Biography
Biography: K. G. Simi
Abstract
A case of the drastic effects of an eastward prompt penetration and a westward overshielding electric field successively affecting the daytime equatorial ionosphere during the space weather event that occurred on 24 November 2001 is presented. Under the influence of the strong eastward prompt penetration electric field starting from 11:25 Indian standard time (IST), the equatorial electrojet (EEJ) strength reached the maximum value of 225 nT at 12:42 IST, almost 7 times greater than the monthly quiet time mean at the same time. This peak EEJ value exceeds the maximum observed values during the month of November for the entire solar cycle by more than 100 nT, irrespective of quiet or disturbed conditions. Further, owing to an ensuing overshielding event that occurred during the main phase of the storm rather than the end of the main phase, this unusually large EEJ showed an equally strong polarity reversal along with a weakening of the sporadic E layer over the equator. The EEJ strength was reduced from +225 to - 120 nT at ~ 13:45 IST, resulting in a strong counter electrojet condition. The latitudinal variation of the F region electron density data from the CHAMP satellite reveal an ill-developed equatorial ionization anomaly at 17:00 IST (11:24 UT) over the Indian sector due to this significant weakening of the zonal electric field. Unlike other geomagnetic storm events, the event reported here occurs in the main phase of the storm, and the main phase continues even after the overshielding event. Hence, this overshielding event does not trigger the recovery of the storm, although there is a reduction in the convection due to the northward turning of the IMF Bz. Interestingly, the overshielding does trigger the recovery of the substorm.