Abstract
AbstractThe configuration of the Earth's main magnetic field and its secular variation are greatly controlled by the nondipole field. This portion of the main field exhibits as 5 planetary‐scale magnetic anomalies in Australia, Africa, Eurasia, North America, and South Atlantic Ocean, as well as a few minor anomalies. Only anomaly in the equatorial region is the Africa anomaly, which affects seriously the shape and position of the magnetic equator, pushing the equator northward for 15° at maximum. The fast westward drift of the Africa anomaly results in a major secular variation cell (Żmax > 200 nT/a for 1900~2005) in Central America on the west of the anomaly. In addition, the secular variations of the Africa and South Atlantic Ocean anomalies seriously distort the geomagnetic field in the western hemisphere, implying its causal relation with the polarity reversed patches on the core‐mantle boundary.
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