1991 年 43 巻 4 号 p. 307-317
The separation of the field of secular variations into the drifting and non-drifting parts by methods worked out by Yukutake and James-Nevanlinna is discussed. The reliability of these techniques is studied on the basis of the international geomagnetic reference field (IGRF) data. The conclusion is drawn about the statistical insignificance of the results of the separation. Using multipole analysis, the authors reject the hypothesis that the multipole grows (decays) and undergoes a rigid rotation around an axis without any structural changes.