Effects of counter electrojet on total electron content over the African equatorial/low-latitude ionosphere during the minimum phase of Solar Cycle 24

Imoleayo Deborah  Adewoyin; Elijah Oyedola  Oyeyemi; Andrew Oke-‘Ovie  Akala

Imoleayo Deborah Adewoyin Department of Physics, University of Lagos, Akoka, Yaba, Lagos, Nigeria
Elijah Oyedola Oyeyemi Department of Physics, University of Lagos, Akoka, Yaba, Lagos, Nigeria
Andrew Oke-‘Ovie Akala Department of Physics, University of Lagos, Akoka, Yaba, Lagos, Nigeria

Keywords: Counter electrojet, total electron content, ionosphere, low latitude

Abstract

This study investigates the effects of Counter Electrojet (CEJ) on Total Electron Content (TEC) over the African equatorial/low-latitude regions during a solar minimum year (2009). TEC data were obtained from three Global Positioning System (GPS) receivers. Horizontal magnetic field data that were used to determine CEJ values were obtained from two ground-based magnetometers. The magnetometers are located at Yaoundé: Geographic latitude (GLAT) 3.85°N, geographic longitude (GLON) 11.50°E, magnetic latitude (MLAT) 5.30^oS; and Ilorin: 8.50°N, 4.67°E, 1.82^oS; while the GPS receivers are located at Libreville: 0.35°N, 9.67°E, 8.05^oS; Yamoussoukro: 6.87°N, 5.24°W, 1.81^oS; and Rabat: 33.9°N, 6.85°W, 27.92^oN. We adopted the K planetary index criterion of Kp ≤ 3 to define the geomagnetically quiet days, in addition to the confirmation with the International Quiet Days (IQDs) listing. Out of all the quiet days of each month, ten days; five CEJ days and five days without CEJ (equatorial electrojet (EEJ) days) were selected. Our results showed that CEJ occurrences clearly suppressed the daily TEC variations. We attributed this suppression in TEC to the reversal of EEJ from eastward to westward direction. TEC enhancement was observed during days without CEJ, and the higher the strength of CEJ, the higher the extent of modification that it imposes on TEC variation. Generally, the extent of TEC variation during CEJ events is more significant in Libreville (near the southern Equatorial Ionization Anomaly (EIA) crest) and least significant in Rabat (outside the EIA band). Furthermore, CEJ-induced variations in TEC exhibit monthly characteristics; TEC suppression was observed 2-3 hours before CEJ onset time in February, March, April and August. However, the suppression in TEC in January, May, June, and July was observed at about 1-2 hours after the onset of CEJ.