Westward drift of the geomagnetic anomaly in East Asia

The westward drift is one of the most important characteristics of the secu lar variation in the Earth's main magnetic field. The most obvious westward drift occurs in the non-dipole magnetic fields. In this paper we analyzed East Asia geomagnetic anomaly by using the correlation analysis of moving r andom pattern based on the International Geomagnetic Reference Field (IGRF) from 1900 to 2000. The time variations of geomagnetic drift vector are obt ained for X, Y and Z component anomalies. Z component anomaly, which illust rates best the geomagnetic drift, drifted westward at a velocity of 0.07 de grees/a in the 100 years. This is obviously slower than the global average westward drift of 0.2 degrees/a. In addition the Z component anomaly slowly drifted northward at a speed of 0.07 degrees/a. Further analyses indicate that there are three stages of the drift of East Asia geomagnetic anomaly. First, the westward drift was fast from 1900 to 1930, with an average speed of 0.10 degrees/a, Then, the drift changed northwest from 1930 to 1980. Th e westward speed was 0.07 degrees/a and northward speed was 0.04 degrees/a during this period. Finally, the drift almost stopped after 1980, and may c hange eastward.