Solar cycle and seasonal variation of spread-F near the magnetic equator

Abstract

Spread-F at equatorial stations, Ibadan, Djibouti and Kodaikanal is shown to increase with increasing solar activity. At Huancayo and other stations in the American zone there is least occurrence of spread-F in years of high solar activity. The seasonal variation of spread-F is greatest at stations in the American zone with a maximum in December and a minimum in June. At African stations a smaller seasonal variation is seen with maximum in June and minimum in December. At Asian stations the seasonal variation of spread-F is very small.