Sq current effects on the seasonal variations in the E-region of the ionosphere

Abstract The index n that describes the seasonal variation of the E -region critical frequency has been obtained for a large number of I.G.Y. stations. Charts are given that show the variation of this index with latitude and local tune, for three different longitude zones. The contours of constant n exhibit asymmetries in latitude, time and magnitude. These asymmetries correlate closely with corresponding asymmetries in the S q current system.