Seasonal & Sunspot-cycle Effects in the Occurrence of Equatorial Spread-F Configurations

Abstract

A study has been made of the seasonal and solar cycle changes in the occurrence of the range- and frequency-type of spread-F at Kodaikanal (geomag, lat" 0'6o N; dip, 3'5 o N) using ionogram data for the period 1957-69. It is found that the range type of spread-F IS the predominant configuration on ionograms at Kodaikanal at any time o year. The occurrence of the frequency type of spread-F-shows a significant positive correlation with sunspot number irrespective of season while that of range-type spread-F shows such behaviour only during local summer months, A comparison of the behaviour of spread-F configurations at Kodaikanal with those at Huancayo reported recently indicates striking longitudinal dependence of the seasonal and solar cycle effects in the occurrence of the two basic forms of spread-F on equatorial ionograms.