Geomagnetic Field Variations along the African Geomagnetic Equator During Recovery Phases of 5th July 2011 and 16th July 2012 Geomagnetic Storms

This paper presents results on an investigation on storm time variation of Earth’s magnetic field along the African geomagnetic equator during the recovery phases of the 5th July 2011 and 16th July 2012 geomagnetic storms. Magnetic field measurements were obtained from the International Real-time Magnetic Observatory Network (INTERMAGNET) stations in Ethiopia, Addis Ababa (AAE) and Mbour (MBO) in Senegal and African Meridian B-field Education and Research (AMBER) network at Yaoundé (CMRN) in Cameroon. The storm time daily variations were derived by subtracting the baseline of three days before the storm and after the storm days of the 5th July 2011 and16th July 2012 geomagnetic storms from each disturbed day. The obtained disturbance daily variations were used to calculate the perturbations of the recovery phases of the storms. The results showed that all the three stations displayed variations in storm time behavior during the recovery phases of the 5th July 2011 and 16th July 2012 geomagnetic storms, which were linked to the effect of Equatorial Electrojet current and the influence of meridional winds and tidal waves. There was also a noticeable reduction in the storm time variation of geomagnetic field at local noon (11:00 - 13:00LT) over the all the three stations during the recovery phases of both storms. This was attributed to the effect of equatorial electrojet (EEJ) and the disturbance dynamo electric fields (DDEF) coming from the high-latitude regions. The reduction in the depth of the storm time variation of geomagnetic field depended on the strength of the storm. The storm time variations of geomagnetic field over the three stations also displayed small irregular and inconsistent patterns (perturbations), which were associated with the ionospheric disturbances coming from the effects of the geomagnetic storms, such as ring current decay, solar wind and Interplanetary magnetic field (IMF) effect and wave-particle interactions.