Study of the geomagnetic anomaly during sunspot maximum

Abstract

The data on the critical frequency of the F2-layer and N( h) profiles obtained for a number of stations during the IGY have been utilized in this paper in a study of the geomagnetic anomaly in the F2-region. Data for the months of September 1957 and March 1958 have been considered as representative of the equinoxial months during a year of high sunspot activity. Using the N( h) profile data, the subpeak electron content of the ionosphere has been obtained. Curves showing the latitudinal variation of maximum electron density ( N m F2) and of subpeak electron content ( n t ) have been drawn and compared for all the even hours of the day. The following facts are observed: Starting as a flat one before sunrise, the maximum electron density curve develops an equatorial maximum after sunrise. This maximum becomes strong at 1000 hours local time. At 1200 hours this maximum shifts to the middle latitudes (between 30° and 40°) leading to a shallow trough at the equator. The trough becomes more pronounced during later hours and is maintained up to midnight. From then onwards it gradually disappears, giving rise once again to the flat curve observed just before sunrise. The subpeak electron content curves show a similar trend. The daytime maximum of the curve is, however, between latitudes 15° and 20°. Comparing the maximum electron density curves obtained above with those obtained during a year of sunspot minimum activity, the trends are seen to be similar. The equatorial trough, however, develops much earlier (3–4 hr) and also disappears much earlier during the sunspot minimum year. Diurnal variation curves for both maximum electron density and subpeak electron content for the magnetic latitudes 0–60°N have been drawn at intervals of 10° and compared. The variations of subpeak electron content are smoother. Martyn's theory of horizontal divergence of ionizaton from the magnetic equator accounts for the general features observed here. But the phase shift between the sunspot minimum and maximum years remains to be explained.