Quiet Time Geomagnetic Field Variations in the Equatorial East African Region During the Inclining Phase of Solar Cycle 24

Abstract

In the present paper, geomagnetic field data obtained from magnetometer measurements at two ground based stations have been used to study solar activity dependence of the solar quiet variations. The study has focused on the horizontal component of the geomagnetic field. The data used in the current study was obtained for all quiet periods from the solar minimum year (2009) through the solar maximum year (2014) to the start of the declining phase (year 2015) of Solar Cycle 24. The present study uses the magnetic data from International Real-time Magnetic Observatory Network (INTERMAGNET) station at Addis Ababa (geomagnetic latitude 0.18°N, geomagnetic longitude110.47°E) and MAGnetic Data Acquisition System (MAGDAS) station at Nairobi (geomagnetic latitude 10.65°S, geomagnetic longitude 108.18°E). The amplitude of mean Sq(H) has shown a dependence on local time of the day and solar activity, with peak values occurring between 1100 LT and 1200 LT and increasing with increase in solar activity; attaining highest values during the solar maximum year. Further, the amplitude of mean Sq(H) at Nairobi is higher than the corresponding values at Addis Ababa in the morning hours around 0700- 0800 LT. The local time dependence is attributed to the variation in solar heating and ionization rates while the solar activity dependence is attributed to the increase in electron density with increase in solar activity. The larger morning hours’ amplitudes at Nairobi than Addis Ababa are possibly due to counter electrojet effects close to the geomagnetic equator