Occurrence of an Additional Layer in the Daytime F Region over Ilorin, Nigeria
An additional stratification in the daytime F region of the equatorial ionosphere within 10 magnetic latitude, known as F3 layer, has been observed and reported for the South American and Asian sectors of the equatorial ionosphere. All the available ionograms recorded at Ilorin (Latitude 8.48 N, Longitude 4.67 W, dip 3.3 S) have been used to study the occurrence of the F3 layer. The study covers a period of 6 years (i.e., 2002, 20052008 and 2010). The results obtained showed a distinct F3 layer during low solar activity whereas the layer was not distinct during high solar activity. The duration of occurrence of the F3 layer ranges from about 15 minutes to 7 hours. The duration of occurrence seemed to be higher during low solar activity although no clear trend in solar activity was observed. The virtual peak height of the F3 layer ¬†as observed in Ilorin ranges from 484 km to 700 km, and the critical plasma frequency of the F3 layer ¬†exceeds that of F2 layer ¬†by 0.58 MHz to 1.01 MHz. The percentage of occurrence of the F3 layer seems to decrease with increase in solar activity.