A generating process of geomagnetic drifting field
Abstract The geomagnetic field is comprised of drifting and standing fields. The drifting field has two remarkable features. One is predominance of sectorial harmonics when the field is expressed in a spherical harmonic series, and the other is uniform drift rate irrespective of harmonics. We consid...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
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SpringerOpen
2018-09-01
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| Series: | Earth, Planets and Space |
| Subjects: | |
| Online Access: | http://link.springer.com/article/10.1186/s40623-018-0908-3 |
| _version_ | 1818194809077104640 |
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| author | Takesi Yukutake Hisayoshi Shimizu |
| author_facet | Takesi Yukutake Hisayoshi Shimizu |
| author_sort | Takesi Yukutake |
| collection | DOAJ |
| description | Abstract The geomagnetic field is comprised of drifting and standing fields. The drifting field has two remarkable features. One is predominance of sectorial harmonics when the field is expressed in a spherical harmonic series, and the other is uniform drift rate irrespective of harmonics. We consider that the drifting field is a product of interaction of the core flow with the axial dipole field near the surface of the core. The key to the predominance of sectorial harmonics is in the boundary condition on the electric current at the core–mantle boundary. If we take the mantle to be an electrical insulator, the electric current normal to the boundary must vanish. This strongly constrains the surface flow. The toroidal flow becomes the flow with the sectorial harmonics predominant. Then, the sectorial toroidal flow, interacting with the axial dipole field, induces the poloidal field in which the sectorial harmonics are predominant. This is the observed type of drifting field. The uniform drift rate, the second nature of the drifting field, seems to suggest that the surface part of the core is rotating westwards as a whole. Subsequently, the sectorial type toroidal flow embedded in the westward-rotating surface layer is considered as the cause of the drifting field. |
| first_indexed | 2024-12-12T01:08:11Z |
| format | Article |
| id | doaj.art-b79e55126fde49fe88af9657b25be186 |
| institution | Directory Open Access Journal |
| issn | 1880-5981 |
| language | English |
| last_indexed | 2024-12-12T01:08:11Z |
| publishDate | 2018-09-01 |
| publisher | SpringerOpen |
| record_format | Article |
| series | Earth, Planets and Space |
| spelling | doaj.art-b79e55126fde49fe88af9657b25be1862022-12-22T00:43:32ZengSpringerOpenEarth, Planets and Space1880-59812018-09-0170112010.1186/s40623-018-0908-3A generating process of geomagnetic drifting fieldTakesi Yukutake0Hisayoshi Shimizu1Earthquake Research Institute, University of TokyoEarthquake Research Institute, University of TokyoAbstract The geomagnetic field is comprised of drifting and standing fields. The drifting field has two remarkable features. One is predominance of sectorial harmonics when the field is expressed in a spherical harmonic series, and the other is uniform drift rate irrespective of harmonics. We consider that the drifting field is a product of interaction of the core flow with the axial dipole field near the surface of the core. The key to the predominance of sectorial harmonics is in the boundary condition on the electric current at the core–mantle boundary. If we take the mantle to be an electrical insulator, the electric current normal to the boundary must vanish. This strongly constrains the surface flow. The toroidal flow becomes the flow with the sectorial harmonics predominant. Then, the sectorial toroidal flow, interacting with the axial dipole field, induces the poloidal field in which the sectorial harmonics are predominant. This is the observed type of drifting field. The uniform drift rate, the second nature of the drifting field, seems to suggest that the surface part of the core is rotating westwards as a whole. Subsequently, the sectorial type toroidal flow embedded in the westward-rotating surface layer is considered as the cause of the drifting field.http://link.springer.com/article/10.1186/s40623-018-0908-3Geomagnetic secular variationWestward driftSectorial harmonicsFlow in Earth’s core |
| spellingShingle | Takesi Yukutake Hisayoshi Shimizu A generating process of geomagnetic drifting field Earth, Planets and Space Geomagnetic secular variation Westward drift Sectorial harmonics Flow in Earth’s core |
| title | A generating process of geomagnetic drifting field |
| title_full | A generating process of geomagnetic drifting field |
| title_fullStr | A generating process of geomagnetic drifting field |
| title_full_unstemmed | A generating process of geomagnetic drifting field |
| title_short | A generating process of geomagnetic drifting field |
| title_sort | generating process of geomagnetic drifting field |
| topic | Geomagnetic secular variation Westward drift Sectorial harmonics Flow in Earth’s core |
| url | http://link.springer.com/article/10.1186/s40623-018-0908-3 |
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