It is shown that sufficiently reliable coefficients of spherical harmonic series for the geomagnetic secular change are obtainable by comparison of spherical harmonic coefficients of the main field for different epochs spaced at fairly long'intervals. Then the spherical harmonic coefficients of the secular change gmn and hmn are computed for the epochs 1806, 1857 and 1900, and synthesized to obtain isoporic charts of the non-dipole field. The isoporic charts thus synthesized indicate that the westward drift is the most prevailing feature of the geomagnetic secular variation, in contrast to the non-dipole anomalies most of which remain at the same position and only a few drift westwards. The result that the whole distribution of the secular change drifts westward suggests that the drifting part of the non-dipole field has global distribution as well as the standing part. It is probably due to the predominant standing anomalies which conceal most parts of the drifting anomalies that only a.few of the anomalies can be recognized to be drifting. Poleward shift of the isoporic foci was also noted, but it seems to be associated with a rapid growth of an equatorial zone where the change in the vertical force is negative.|地球磁場経年変化の解析は,固定観測所で観測された磁場の変化率をもととしてなされてきたが,理論的には主磁場解析より得られた球函数係数(gmn, hmn)の時間変化を求めても同一の結果が得られる筈である.この方法を用いて,17世紀以降の経年変化(gmn, hmn)を推定し,非双極子部分の経年変化の時間的変動を調べた.
雑誌名
東京大學地震研究所彙報 = Bulletin of the Earthquake Research Institute, University of Tokyo
巻
46
号
5
ページ
1075 - 1102
発行年
1968-12-20
ISSN
00408972
書誌レコードID
AN00162258
フォーマット
application/pdf
日本十進分類法
453
出版者
東京大学地震研究所
出版者別名
Earthquake Research Institute, University of Tokyo
アイテムへのリンクの際はタイトル右肩にある「Permalink」をご利用ください！
Please use "Permalink" at the top right of the title when linking to items!
52. The Westward Drift of the Geomagnetic Secular Variation
ji0465004.pdf
(1.85MB)
