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《Chinese Journal of Geophysics》 1998-01
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Xu WEN-YAO (Institute of Geophysics. Chinese Academy of Sciences,Beijing 100101, China)SUN WEI (Geophysical Institute, Alaska University, USA Alaska, AK99775-7320)  
Method of natural orthogonal components(MNOC) is used to analyze the spatial structure and secular variation of the earth's main magnetic field on the basis of IGRF models for 1900-2000. The main components (eigen modes) of the main field and their secular variation are obtained. The first eigen mode describes the overall characteristics in the stable structure of the field, and its intensity decreases monotonously. The second eigen mode, with monotonously decreasing intensity,describes the characteristics of the positive anomalies in indian Ocean and Atlantic.The third eigen mode corresponds to positive Caribbean anomaly, varying with a period of 100 years. The fourth eigen mode is characterized by positive North American anomaly and negative South-Asian anomaly, varying with 80 year period.The fifth eigen mode represents smaller scale and faster-varying anomalies. The results show that the magnetic field in the Pacific Ocean monotonously decreases, and has quite stable structure. It can be represented by the 1st mode. On the other hand, the structure in the indian Ocean is more complicated, it is composed of different eigen modes with different periods and spatial structure. The northern, central and southern partS of Atlantic are described by different modes, they have quite different periods.
【Fund】: 国家自然科学基金!49734140
【CateGory Index】: P318.1
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