Seasonal variations of Sq(H) for a chain of geomagnetic observatories in the eastern part of China

The detailed latitudinal sections of seasonal variation of Sq(H) for quiet days are presented, using the method of main component analysis and utilizing data of ten geomagnetic observatories which are well-distributed with latitudes in the eastern part of China. The apparent focal latitude of equivalent current system in the ionosphere is determined; it is shown that the variation of the second eigenvector of Sq(H) is resulted from the deviation of symmetrical axis of equivalent current system from the geomagnetic axis.