Long-term features of drifting and standing non-dipole fields as determined from Holocene palaeomagnetic secular variations |
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Authors: | Chizu Itota Masayuki Hyodo Katsumi Yaskawa |
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Affiliation: | Department of Earth Sciences, College of Humanities and Sciences, Nihon University, Setagaya, Tokyo 156, Japan. E-mail: citota@chs.nihon-u.ac.jp;Research Center for Inland Seas, Kobe University, Nada, Kobe 657, Japan;Osaka College, Hinamikawachi, Osaka 587, Japan |
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Abstract: | Geomagnetic field motions of Holocene secular variations are investigated using a separation method. The palaeomagnetic secular variations from Britain, North America and Australia have been subjected to maximum-entropy method analyses. Based on the results of spectral analyses, the secular variations are separated by band-pass filters into low-frequency components, generally including the period band 1800-3600 yr, and high-frequency components, generally including the period band 1000-1200 yr. There is an interval, from 4200 to 1700 yr BP, which shows clockwise rotational motions in the low-frequency components of all three sites. Westward drifting of geomagnetic fields may be globally dominant. Swinging or elliptical looping motions constrained to a certain direction were observed in the low-frequency components of the British data. The time duration for the persistence of the swinging motion constrained to a certain direction was 3500 years or so, which could be the lifetime of an oscillating stationary field. The duration of the transitional motion was 1000-1300 years, which may indicate the recurrence time of a stationary field. |
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Keywords: | geomagnetic field non-dipole field palaeomagnetism spectral analysis |
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