Secular variation in the geographic location of the dip equator

The geographic location of the dip equator on the globe has been determined for several epochs between 1550 and 1990 A.D. It is shown that two regions near 165°E and 285°E are devoid of migratory changes whereas between 300 and 0°E there is a large northward movement. The period between 1945 and 1990 is marked by a nearly linear change in the latitude of the dip equator while earlier epochs show more complex trends. Consistent with the earlier observations of the movement of the magnetic center towards or away from the centre of the earth, before and after 1800 A.D., the secular curves in certain longitude zones indicate a clear change in pattern. The observed secular variations in the vertical cornponent at several low latitude stations are generally in agreement with the direction of the movement of the dip equator. Examples of unexpected behaviour are highlighted. The eccentric dipole model appears to be adequate to delineate the dip equator for any epoch.