On the Occurrence of Large SSC Amplitudes in the Horizontal Intensity of the Geomagnetic Field in Middle Latitudes Around Local Midnight

Abstract

A study is made of the SSC amplitudes in H in relation to their local time of occurrence in the middle latitudes using data of 10 geomagnetic stations for the period 1953-60. It is found that (1) the greatest SSC amplitudes in H are recorded (in the summer months) around the local midnight (1 to 3 hours before or 1 to 3 hours afterthe local midnight), and (2) the minimum in SSC amplitudes in H occurs (in the winter months) during 18^h-21^h L. T. at the African stations and during 4^h-10^h L. T. (generally around 7^h L. T.) at the other stations.
The midnight maximum amplitude and the morning minimum amplitude are explained in terms of the ionospheric screening effect and precipitation of electrons into the auroral zone ionosphere on the night side of the earth from the outer Van Allen Belt at the time of the SSC.