{"title":"从强磁通量斑块的时间依赖性看区域外核运动学","authors":"Filipe Terra-Nova , Ingo Wardinski","doi":"10.1016/j.pepi.2023.107106","DOIUrl":null,"url":null,"abstract":"<div><p>Observations of the geomagnetic field by surface observatories and dedicated satellite missions such as the Swarm constellation provide constraints on the dynamics in Earth's outer core. In particular, global core flow models estimated by inversion of the radial magnetic induction equation provide an image of the circulation of the electrically conductive fluid at the top of the core. However, in these models the poloidal flow is much less robust than the toroidal core flow. Here, we infer regional outer core kinematics from the temporal variability of high-latitude intense geomagnetic flux patches. We develop an algorithm to fit anisotropic 2D-Gaussians to the shape of those flux patches in order to infer their area, amplitude and level of anisotropy. The temporal variabilities of these properties are used to quantify contraction, expansion, amplification, weakening and horizontal shear. Comparisons with idealized kinematic scenarios based on synthetic field and flow models allow to infer regional outer core kinematics. We found that some geomagnetic flux patches exhibit expansion and weakening corresponding to fluid upwellings, whereas other patches exhibit contraction and intensification corresponding to downwellings. In both cases the patches' area and amplitude relations follow hyperbolic curves. Our results show that the geomagnetic flux patches are affected by upwelling more often than by downwelling during the historical period. Equatorially symmetric poloidal flow prior to <span><math><mo>≈</mo><mn>1910</mn></math></span> is inferred for the western intense patches. Kinematic scenarios where the field and flow structures centers coincide failed to reproduce the geomagnetic flux patches behavior. We recover the flux concentration efficiency of intense geomagnetic flux patches with an upwelling that resides two times its radius size away from the center of the flux patch. We also found a significant level of anisotropy over long periods for the historical geomagnetic flux patches. Anisotropic magnetic flux patches that are elongated in the direction of the shear flow may explain the east-west oriented present-day field at high latitudes of the southern Hemisphere. Overall, stretching effects at the top of the core can be deduced from our analysis of regional SV and allow further inferences on the poloidal part of the core flow.</p></div>","PeriodicalId":54614,"journal":{"name":"Physics of the Earth and Planetary Interiors","volume":"344 ","pages":"Article 107106"},"PeriodicalIF":2.4000,"publicationDate":"2023-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Regional outer core kinematics from the time dependence of intense geomagnetic flux patches\",\"authors\":\"Filipe Terra-Nova , Ingo Wardinski\",\"doi\":\"10.1016/j.pepi.2023.107106\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>Observations of the geomagnetic field by surface observatories and dedicated satellite missions such as the Swarm constellation provide constraints on the dynamics in Earth's outer core. In particular, global core flow models estimated by inversion of the radial magnetic induction equation provide an image of the circulation of the electrically conductive fluid at the top of the core. However, in these models the poloidal flow is much less robust than the toroidal core flow. Here, we infer regional outer core kinematics from the temporal variability of high-latitude intense geomagnetic flux patches. We develop an algorithm to fit anisotropic 2D-Gaussians to the shape of those flux patches in order to infer their area, amplitude and level of anisotropy. The temporal variabilities of these properties are used to quantify contraction, expansion, amplification, weakening and horizontal shear. Comparisons with idealized kinematic scenarios based on synthetic field and flow models allow to infer regional outer core kinematics. We found that some geomagnetic flux patches exhibit expansion and weakening corresponding to fluid upwellings, whereas other patches exhibit contraction and intensification corresponding to downwellings. In both cases the patches' area and amplitude relations follow hyperbolic curves. Our results show that the geomagnetic flux patches are affected by upwelling more often than by downwelling during the historical period. Equatorially symmetric poloidal flow prior to <span><math><mo>≈</mo><mn>1910</mn></math></span> is inferred for the western intense patches. Kinematic scenarios where the field and flow structures centers coincide failed to reproduce the geomagnetic flux patches behavior. We recover the flux concentration efficiency of intense geomagnetic flux patches with an upwelling that resides two times its radius size away from the center of the flux patch. We also found a significant level of anisotropy over long periods for the historical geomagnetic flux patches. Anisotropic magnetic flux patches that are elongated in the direction of the shear flow may explain the east-west oriented present-day field at high latitudes of the southern Hemisphere. Overall, stretching effects at the top of the core can be deduced from our analysis of regional SV and allow further inferences on the poloidal part of the core flow.</p></div>\",\"PeriodicalId\":54614,\"journal\":{\"name\":\"Physics of the Earth and Planetary Interiors\",\"volume\":\"344 \",\"pages\":\"Article 107106\"},\"PeriodicalIF\":2.4000,\"publicationDate\":\"2023-09-22\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Physics of the Earth and Planetary Interiors\",\"FirstCategoryId\":\"89\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0031920123001322\",\"RegionNum\":3,\"RegionCategory\":\"地球科学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"GEOCHEMISTRY & GEOPHYSICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physics of the Earth and Planetary Interiors","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0031920123001322","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOCHEMISTRY & GEOPHYSICS","Score":null,"Total":0}
Regional outer core kinematics from the time dependence of intense geomagnetic flux patches
Observations of the geomagnetic field by surface observatories and dedicated satellite missions such as the Swarm constellation provide constraints on the dynamics in Earth's outer core. In particular, global core flow models estimated by inversion of the radial magnetic induction equation provide an image of the circulation of the electrically conductive fluid at the top of the core. However, in these models the poloidal flow is much less robust than the toroidal core flow. Here, we infer regional outer core kinematics from the temporal variability of high-latitude intense geomagnetic flux patches. We develop an algorithm to fit anisotropic 2D-Gaussians to the shape of those flux patches in order to infer their area, amplitude and level of anisotropy. The temporal variabilities of these properties are used to quantify contraction, expansion, amplification, weakening and horizontal shear. Comparisons with idealized kinematic scenarios based on synthetic field and flow models allow to infer regional outer core kinematics. We found that some geomagnetic flux patches exhibit expansion and weakening corresponding to fluid upwellings, whereas other patches exhibit contraction and intensification corresponding to downwellings. In both cases the patches' area and amplitude relations follow hyperbolic curves. Our results show that the geomagnetic flux patches are affected by upwelling more often than by downwelling during the historical period. Equatorially symmetric poloidal flow prior to is inferred for the western intense patches. Kinematic scenarios where the field and flow structures centers coincide failed to reproduce the geomagnetic flux patches behavior. We recover the flux concentration efficiency of intense geomagnetic flux patches with an upwelling that resides two times its radius size away from the center of the flux patch. We also found a significant level of anisotropy over long periods for the historical geomagnetic flux patches. Anisotropic magnetic flux patches that are elongated in the direction of the shear flow may explain the east-west oriented present-day field at high latitudes of the southern Hemisphere. Overall, stretching effects at the top of the core can be deduced from our analysis of regional SV and allow further inferences on the poloidal part of the core flow.
期刊介绍:
Launched in 1968 to fill the need for an international journal in the field of planetary physics, geodesy and geophysics, Physics of the Earth and Planetary Interiors has now grown to become important reading matter for all geophysicists. It is the only journal to be entirely devoted to the physical and chemical processes of planetary interiors.
Original research papers, review articles, short communications and book reviews are all published on a regular basis; and from time to time special issues of the journal are devoted to the publication of the proceedings of symposia and congresses which the editors feel will be of particular interest to the reader.