Geomagnetic activity control of irregularities occurrences over the
crests and trough of the African EIA
Abstract
This paper examined the behavior of ionospheric irregularities over the
African Equatorial Ionization Anomaly (EIA) during intense geomagnetic
storms which occurred from 2012 to 2015. Total electron content (TEC)
data was used to derive the rate of change of TEC index (ROTI). This was
employed to monitor irregularities over the trough and crests of the
EIA. Variations of the horizontal component of the Earth’s magnetic
field (H) were examined. The H component was additionally used to
compute ionospheric electric current disturbance (Diono). Prompt
penetration electric field (PPEF) inferred from variations of Diono was
compared with PPEF obtained from the Prompt Penetration Equatorial
Electric Field Model (PPEFM). The PPEFM predicted accurately all PPEFs
thus, was found to be valid over the African EIA. The local time of
occurrence of interplanetary magnetic field (IMF ) dictated the behavior
of irregularities. Eastward PPEF triggered short duration irregularities
on 23 April 2012, 17 March 2013 and 20 February 2014 while westward
disturbance dynamo electric field (DDEF) reduced them thereafter. During
the storms recovery including the 15 July 2012 and 17 March 2015 events,
irregularities were suppressed by westward DDEF. However, during the
storms of 14 November 2012 and 29 June 2013 no irregularities were
observed. Irregularities were always inhibited over the trough. The
inhibition lasted longer during the super storm of March 2015. Over the
crests, there were differences in their behavior on 16-17 July 2012, 15
November 2012 and 19 March 2013. These were however, not linked to
storm-time electric field.