analysis of the geomagnetic secular variation in the 20th century.
20世纪地磁长期变化场分析

Using IGRF(International Geomagnetic Reference Field) workout by IAGA (International Association of Geomagnetism and Aeronomy), this paper investigates the geomagnetic field in the 20th century. The quadrupole field ( n =2) is the most significant one of the geomagnetic secular variation in the 20th century. The Gauss series of the geomagnetic secular variation is converged slower than that of the main field. Using the method of tracing the change of the position of the anomaly focus, it is found that there are 5 anomalies in the chats of Z (vertical component) of the secular variation of the non dipole field. Their drifting is not consolidate in a few degrees. But they are drifting westward basically. This inconsistency of the westward drifting of the geomagnetic secular variation proves the Wang's geomagnetic model in some degrees. Different from the geomagnetic main field, the power spectra of the dipole, quatrupole and the eighthpole field of the secular variation have significant changes.