On the geomagnetic secular variation in the Pacific region

Autor: Hisayoshi Shimizu, Takesi Yukutake
Rok vydání: 2018
Předmět:
Zdroj: Physics of the Earth and Planetary Interiors. 283:122-130
ISSN: 0031-9201
DOI: 10.1016/j.pepi.2018.08.008
Popis: It is widely believed that in the Pacific region the geomagnetic secular variation is low and that the non-dipole field is weak. This is also known as hemispherical asymmetry between the Pacific and the Atlantic hemispheres, representing the low secular variation in the Pacific hemisphere. With this characteristic feature, a question has been left unsolved whether it is a permanent feature or a transient one. Reexamination of the geomagnetic field for the past 400 years indicates that in the early 17th century the non-dipole field was not weak, nor the secular variation was low in the Pacific region, implying that the hemispherical asymmetry is not a permanent phenomenon. This paper examines the secular variation for the past 400 years from viewpoint of drifting and standing field model. It has been found that the low secular variation in the Pacific region is mainly caused by the drift of the drifting field. At the Earth’s surface the drifting field is dominated by spherical harmonics Y 2 2 ( θ , ϕ ) with two pairs of ridges and troughs with their axes aligned in the meridional direction. The two pairs are not equal; one pair is stronger than the other. Movements of the different magnitude of the pairs are considered to have caused the hemispherical asymmetry of the secular variation for recent years, giving rise to the non-weak field in the Pacific region in the early 17th century.
Databáze: OpenAIRE
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