Variations of Spread-F Occurrence Rates at Near-equatorial Stations in the Australasian Zone

Abstract

The occurrence rates of spreadF for selected years between 1964 and 1972 are presented for three Australian stations lying between 10� and 25� magnetic latitude. Spreading is mainly of the rangespreading type. Two types of spread F are observed: one occurs during the solstices and correlates negatively with sunspot number; the other occurs during the equinoxes and correlates positively with sunspot number and negatively with magnetic activity. The relative importance of the two types is found to vary with latitude.