Systematic ionospheric changes associated with geomagnetic activity

Systematic changes of maximum electron‐density associated with geomagnetic disturbance have been difficult to isolate owing to the lack of sufficient homogeneous data. It is well known that intense magnetic storms are associated with marked ionospheric changes. The purpose of this investigation is to determine the nature of systematic changes of maximum ion‐density of F 2 ‐layer which accompany geomagnetic disturbance of all ranges of intensity at several latitudes. Appleton, Naismith, and Ingram [see 1 of “References” at end of paper] have shown that at Tromsö and at Slough there are, associated with geomagnetic disturbance, characteristic variations in F 2 ‐1ayer which change with season. Similar changes have been observed at the Kensington (Maryland) Experimental Station and described qualitatively [2]. In the present investigation we consider about two years of continuous observations made at the Watheroo and Huancayo magnetic observatories of the Department of Terrestrial Magnetism utilizing automatic multifrequency technique described elsewhere [3, 4]. A convenient quantitative measure, namely, deviation of daily average maximum electron‐density from normal, has been derived and compared to associated geomagnetic activity for each day.