| 地磁场长期变化速率的30年周期 |
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| 引用本文： | 徐文耀,魏自刚,杜爱民.地磁场长期变化速率的30年周期[J].地球物理学报,2006,49(5):1329-1338. |
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| 作者姓名： | 徐文耀 魏自刚 杜爱民 |
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| 作者单位： | 1.中国科学院地质与地球物理研究所, 北京 100029 2 Laboratoire de Geophysique Interne et Tectonophysique, Grenoble, France |
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| 摘 要： | 地球主磁场B和它的长期变化都起源于地球外核的磁流体发电机过程，但是，它们的空间结构和时间演化特征却有很大差异. 本文采用全球平均的“无符号年变率”X〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Y〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Z〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、H〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗和F〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗来表征长期变化场〖WTHX〗〖AKB·〗〖WTBZ〗的总体强度，利用第9代国际参考地磁场模型IGRF 9，研究〖WTHX〗〖AKB·〗场的变化特征. 结果表明，在1900～2000年的100年当中，〖AKB·〗场经历了3幕变化，最大年变率分别发生在1910～1920、1940～1950、1970～1980年，显示出清晰的30年周期变化，而且，每一周期的上升段比其下降段短得多. 研究结果还表明，非偶极场对〖AKB·〗的贡献约为偶极场的2倍，因此，决定〖AKB·〗场周期特征的主要因素是非偶极场（特别是四极子场），而不是偶极子场. 这一特点与主磁场B〖WTBZ〗中偶极场占绝对优势的特点完全不同.
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| 关 键 词： | 主磁场 长期变化 偶极磁场 非偶极磁场 无符号年变率 |
| 文章编号： | 0001-5733（2006）05-1329-10 |
| 收稿时间： | 2005-12-12 |
| 修稿时间： | 2005-12-122006-05-08 |
Thirty_year period in secular variation rate of the main geomagnetic field |
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| XU Wen-Yao,Henri-Claud Nataf,WEI Zi-Gang,DU Ai-Min.Thirty_year period in secular variation rate of the main geomagnetic field[J].Chinese Journal of Geophysics,2006,49(5):1329-1338. |
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| Authors: | XU Wen-Yao Henri-Claud Nataf WEI Zi-Gang DU Ai-Min |
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| Institution: | 1.Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2 Laboratoire de Geophysique Interne et Tectonophysique, Grenoble, France |
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| Abstract: | The main geomagnetic field, 〖WTHX〗B〖WTBZ〗, and its secular variation,〖WTHX〗〖AKB·〗〖WTBZ〗,originate from same dynamo process in the outer core. Their spatial structure and temporal behaviors, however, are drastically different. Using ‘globally averaged unsigned annual rate', 〖WTBX〗X〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Y〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、Z〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗、H〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗〖WTBZ〗 and 〖WTBX〗F〖DD(-*3〗〖KG*2/3〗·〖DD)〗〖DD(-*2〗〖KG*2/3〗—〖DD)〗〖WTBZ〗, to express the magnitude of the 〖WTHX〗〖AKB·〗〖WTBZ〗_field, we studied periodicity in the 〖WTHX〗〖AKB·〗〖WTBZ〗_field on the basis of IGRF_9 models. The results show that the 〖WTHX〗〖AKB·〗〖WTBZ〗_field experienced a three_episode variation during the centennial period from 1900 to 2000 The maximum annual rates occurred around 1910～1920, 1940～1950, and 1970～1980, respectively, showing a 30_year period. In addition, the rising phase in each episode is much shorter than declining phase. The governing factor of this periodic variation is the non_dipole field, mainly the quatrupole, instead of the dipole field, although the dipole field is dominative over all other multiples in the main field 〖WTHX〗B〖WTBZ〗. |
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| Keywords: | Main geomagnetic field Secular variation Dipole field Non-dipole field Unsigned annual rate |
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