东亚大陆磁异常的西向漂移

WESTWARD DRIFT OF THE GEOMAGNETIC ANOMALY IN EAST ASIA

西向漂移是地磁场长期变化最重要的特点之一，而西漂最显著的部分是非偶极子场部分．本文以１９００-２０００年国际参考地磁场（ＩＧＲＦ）为依据，运用无线电科学中的"移动变形图案相关分析"方法对近百年来东亚大陆磁异常的漂移运动进行了分析，得到磁异常各分量漂移矢量随时间的变化．结果表明，最能代表地磁场西漂特征的Ｚ分量异常近百年来平均西漂速度为０.０７°／ａ，明显小于全球磁场西漂的平均速度０．２°／ａ．Ｚ分量还显示出０.０２°／ａ的缓慢北向漂移．详细分析还表明，东亚大陆磁异常的漂移分为３个阶段：１９００-１９３０年为较快的西漂，平均速度为０.１０°／ａ；１９３０-１９８０年为西北向漂移，平均西漂速度分量０．０７°／ａ，北漂速度分量为０．０４°／ａ；１９８０年后漂移几乎停止，并有转为东漂的迹象．

The westward drift is one of the most important characteristics of thesecular variation in the Earth's main magnetic field. The most obvious westward driftoccurs in the non-dipole magnetic fields. In this paper we analyzed East Asiageomagnetic anomaly by using the correlation analysis of moving random patternbased on the international Geomagnetic Reference Field (IGRF) from 1900 to 2000.The time variations of geomagnetic drift vector are obtained for X Y and Z componentanomalies. Z component anomaly, which illustrates best the geomagnetic drift, driftedwestward at a velocity of 0.07°/a in the 100 years. This is obviously slower than theglobal average westward drift of 0.2°/a. In addition the Z component anomaly slowlydrifted northward at a speed of 0.07°/a. Further analyses indicate that there are threestages of the drift of East Asia geomagnetic anomaly. First, the westward drift wasfast from 1900 to 1930, with an average speed of 0.10°/ a. Then, the drift changednorthwest from 1930 to 1980. The westward speed was 0.07°/a and northward speedwas 0.04°/a during this period. Finally, the drift almost stopped after 1980, and maychange eastward.