共查询到20条相似文献，搜索用时 15 毫秒
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D. M. Pechersky G. P. Markov V. A. Tsel’movich Z. V. Sharonova 《Izvestiya Physics of the Solid Earth》2012,48(7-8):653-669
Thermomagnetic and microprobe analyses are carried out and a set of magnetic characteristics are measured for 25 meteorites and 3 tektites from the collections of the Vernadsky Geological Museum of the Russian Academy of Sciences and Museum of Natural History of the North-East Interdisciplinary Science Research Institute, Far Eastern Branch of the Russian Academy of Sciences. It is found that, notwithstanding their type, all the meteorites contain the same magnetic minerals and only differ by concentrations of these minerals. Kamacite with less than 10% nickel is the main magnetic mineral in the studied samples. Pure iron, taenite, and schreibersite are less frequent; nickel, various iron spinels, Fe-Al alloys, etc., are very rare. These minerals are normally absent in the crusts of the Earth and other planets. The studied meteorites are more likely parts of the cores and lower mantles of the meteoritic parent bodies (the planets). Uniformity in the magnetic properties of the meteorites and the types of their thermomagnetic (MT) curves is violated by secondary alterations of the meteorites in the terrestrial environment. The sediments demonstrate the same monotony as the meteorites: kamacite is likely the only extraterrestrial magnetic mineral, which is abundant in sediments and associated with cosmic dust. The compositional similarity of kamacite in iron meteorites and in cosmic dust is due to their common source; the degree of fragmentation of the material of the parent body is the only difference. 相似文献
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Denis E. Winch 《Pure and Applied Geophysics》1989,131(3):533-549
Displayed daygraphs of magnetic observatory hourly mean values and of lunar magnetic variations reconstructed from spherical harmonic coefficients are used to illustrate the difficulties that arise in separating lunar magnetic effects from those associated with the 27 day recurrence tendency in magnetic activity. 相似文献
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An extensive compilation of recently acquired geophysical reconnaissance data has allowed the Mesozoic magnetic lineations (The Eastern Keathley sequence) to be identified and mapped in detail for the area off northwest Africa lying between Madeira and the Cape Verde Islands. These anomalies were generated as one limb of a symmetric spreading center (Paleo Mid-Atlantic Ridge) from about 107 to 153 m.y.B.P. Offsets in the lineation pattern serve to identify fracture zone traces whose trends are approximately east-west. The seaward boundary of the marginal quiet zone does not precisely define an isochron due to the presence of a variable width transition zone of intermediate amplitude magnetic anomalies. Crust underlying the marginal quiet zone was generated, at least in part, during the Jurassic, Graham normal polarity epoch. The quiet zone boundary is not offset significantly on opposite sides of the Canaries lineament as previously suggested. A possible counterpart of the U.S. east coast magnetic anomaly is observed in some areas near the shelf/slope break of Spanish Sahara and Mauritania. The presence of relatively high-amplitude (but not-correlatable) magnetic anomalies seaward of the Mesozoic sequence and presumably generated during the Cretaceous, Mercanton normal polarity epoch remains a paradox. 相似文献
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We determine the nonlinear drift velocities of the mean magnetic field and nonlinear turbulent magnetic diffusion in a turbulent convection. We show that the nonlinear drift velocities are caused by three kinds of the inhomogeneities; i.e., inhomogeneous turbulence, the nonuniform fluid density and the nonuniform turbulent heat flux. The inhomogeneous turbulence results in the well-known turbulent diamagnetic and paramagnetic velocities. The nonlinear drift velocities of the mean magnetic field cause the small-scale magnetic buoyancy and magnetic pumping effects in the turbulent convection. These phenomena are different from the large-scale magnetic buoyancy and magnetic pumping effects which are due to the effect of the mean magnetic field on the large-scale density stratified fluid flow. The small-scale magnetic buoyancy and magnetic pumping can be stronger than these large-scale effects when the mean magnetic field is smaller than the equipartition field. We discuss the small-scale magnetic buoyancy and magnetic pumping effects in the context of the solar and stellar turbulent convection. We demonstrate also that the nonlinear turbulent magnetic diffusion in the turbulent convection is anisotropic even for a weak mean magnetic field. In particular, it is enhanced in the radial direction. The magnetic fluctuations due to the small-scale dynamo increase the turbulent magnetic diffusion of the toroidal component of the mean magnetic field, while they do not affect the turbulent magnetic diffusion of the poloidal field. 相似文献
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A program for identifying magnetic clouds in patrol satellite data, which recorded the interplanetary medium parameters near
the magnetosphere, has been developed based on the cloud model in the form of a force-free cylindrical flux tube. The program
makes it possible to also determine the entire magnetic field distribution in a cloud that approaches the Earth, using the
initial satellite measurements. For this purpose, a model cloud (which has the maximal correlation coefficient with an analyzed
cloud with respect to three magnetic field vector components and minimal rms deviations of the magnetic field and velocity
components) is selected from the preliminarily created database including 2 million model clouds. The obtained magnetic field
distribution in a cloud will make it possible to predict the intensity of a magnetic storm that this cloud will cause. 相似文献
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文采用球坐标下2.5维理想MHD模型,对日球子午面内方位磁场扰动的传播进行数值模拟,重点分析它对行星际磁场螺旋角的影响. 本文认为,观测到的行星际磁场螺旋角大于Parker模型的预言值,是太阳表面不断向行星际发出同向方位磁场扰动的结果;太阳较差自转在太阳内部产生的方位磁场为这类扰动提供了源头. 模拟结果表明,采用持续时间等于周期的十分之一、扰动幅度为103nT量级的正向方位磁场扰动,就可使1 AU处行星际磁场的螺旋角增加2°左右,与有关观测结果相符. 模拟结果还表明,上述方位磁场扰动对日球子午面内的太阳风特性和磁场位形的影响基本上可以忽略. 相似文献
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C.T. Russell 《Physics of the Earth and Planetary Interiors》1979,20(2-4):237-246
The magnetic field measurements of the Mars 2, 3 and 5 spacecraft have been interpreted by Dolginov and co-workers to be consistent with an intrinsic planetary magnetic moment of 2.5 × 1022 gauss cm3. They base this interpretation mainly on the apparent size of the obstacle responsible for deflecting the solar wind, the lack of dependence of the sign of the magnetic field in the wake region of the planet on the sign of the component of the interplanetary field radially out from the sun, and an apparent encounter of the Mars spacecraft with the planetary field. When examined in detail this evidence is very suspect. A detailed criticism of the arguments by Dolginov and co-workers for an intrinsic field has appeared elsewhere. Herein we summarize this criticism and present, in an appendix, a compendium of the Mars 3 and 5 magnetic field data transformed into a coordinate system in which the details of the interaction are more easily visualized. Many of these data have not been published in this form previously. 相似文献
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E. E. Benevolenskaya 《Geomagnetism and Aeronomy》2013,53(7):891-895
The solar polar magnetic field has attracted the attention of researchers since the polar magnetic field reversal was revealed in the middle of the last century (Babcock and Livingston, 1958). The polar magnetic field has regularly reversed because the magnetic flux is transported from the sunspot formation zone owing to differential rotation, meridional circulation, and turbulent diffusion. However, modeling of these processes leads to ambiguous conclusions, as a result of which it is sometimes unclear whether a transport model is actual. Thus, according to the last Hinode data, the problem of a standard transport model (Shiota et al., 2012) consists in that a decrease in the polar magnetic flux in the Southern Hemisphere lags behind such a decrease in the flux in the Northern Hemisphere (from 2008 to June 2012). On the other hand, Svalgaard and Kamide (2012) consider that the asymmetry in the sign reversal simply results from the asymmetry in the emerging flux in the sunspot formation region. A detailed study of the polar magnetic flux evolution according to the Solar Dynamics Observatory (SDO) data for May 2010–December 2012 is illustrated in the present work. Helioseismic & Magnetic Imager (HMI) magnetic data in the form of a magnetic field component along the line of sight (the time resolution is 720 s) are used here. The magnetic fluxes in sunspot formation regions and at high latitudes have been compared. 相似文献
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Tan-Wen Wang 《Annales Geophysicae》1996,14(9):888-892
Fractal theory is applied in a quantitative analysis of geomagnetic storms. Fractal dimensions (D) of the attractor for storm data from the Beijing observatory (40.0°N, 116.2°E) using several time intervals are calculated. A maximum value of 1.4 has been obtained for a geomagnetic storm; on quite days the dimension is only slightly larger than 0.5. Data from two storms are analyzed here. Results show that a combination of both D and the magnetic index, k, can perhaps describe the degree of solar disturbance better than the single parameter k. 相似文献
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Almost 300 years to the day since Edmond Halley's first magnetic chart, the RAS held a Discussion Meeting to commemorate this achievement and to consider Halley's work in navigation and geophysics. David Barraclough and Toby Clark report on the "300th anniversary of the first magnetic chart: Edmond Halley's work in geophysics and navigation". 相似文献
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在地质体具有较强剩磁或自退磁效应的情况下,获得地质体总磁化方向对磁法勘探的数据处理、反演及解释具有重要意义.与传统航磁总场测量相比,航磁矢量(三分量)测量能够获得地磁场的矢量信息.基于三分量磁异常一阶矩与磁源磁矩的积分关系,我们实现了基于航磁矢量数据的磁源总磁化方向估算.针对该方法易受相邻异常影响,从而使多异常的估算难以确定磁源中心位置的问题,分析了在不同磁化倾角下,估算的磁化偏角、倾角与实际磁源中心位置的关系,并根据该关系采取了限定估算区域的方法,获得了多异常的估算结果.将该方法应用于东天山启鑫地区实测航磁三分量数据,估算了具有强剩磁的启鑫岩体总磁化方向,并将估算的方向应用于化极计算.化极结果显示,减少了启鑫岩体磁异常受斜磁化的影响,且与磁异常模量计算结果类似.该方法假设磁源均匀磁化,估算结果可视为地质体总磁化方向的整体体现,对强剩磁地质体磁异常的数据处理、反演及解释具有实际意义. 相似文献
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Some theories predict the magnetosheath magnetic field strength will decrease and the density increase just outside the dayside magnetopause as the interplanetary magnetic field turns southward. Two studies have recently reported results which confirm these expectations. In contrast, we briefly review our own theoretical predictions which indicate that precisely the opposite effect is expected. We survey new and previously reported magnetosheath observations and demonstrate that they are consistent with the predictions of our model. The conflicting results indicate a need for further theoretical and observational work. 相似文献
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《Physics of the Earth and Planetary Interiors》2006,154(3-4):323-336
Low-field variation of magnetic susceptibility was investigated on a collection of several hundreds specimens of various minerals and rocks using the KLY-4S Kappabridge. The measurement is fully automated, being executed in 21 distinct fields ranging from 2 to 450 A/m (in one frequency of 875 Hz). The measurement is rapid, 7 min per specimen, so that large collections of specimens can be investigated. The results can be processed both graphically and mathematically. For the latter processing, parameters of two kinds were introduced. One characterizes the susceptibility change with field, the other one characterizes the field in which the susceptibility no longer obeys the Rayleigh law and starts becoming more complex.The results were evaluated statistically. Remarkable differences were revealed between individual minerals and between some rock types. For example, the field variation of susceptibility of pyrrhotite is in general an order of magnitude larger than that of titanomagnetite. The susceptibility increase in pyrrhotite starts at the field an order of magnitude lower than that of titanomagnetite. Low-field variation of susceptibility then appears as an interesting phenomeon that helps in the identification of magnetic minerals and in some cases also in assessing the compositional variation of them. 相似文献
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《Physics of the Earth and Planetary Interiors》2005,148(2-4):149-156
Early in the history of planetary evolution portions of Martian crust became magnetized by dynamo-generated magnetic field. A lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo. This ambient field is capable of magnetizing portions of deeper crust that cools through its blocking temperatures in an absence of dynamo. We consider both magnetite (Fe3O4) and hematite (α-Fe2O3) as minerals contributing to the overall magnetization. Analysis of magnetization of magnetic minerals of various grain size and concentration reveals that magnetite grains less than 0.01 mm in size, and hematite grains larger than 0.01 mm in size can become effective magnetic source capable of magnetizing magnetic minerals contained in surrounding volume. Preexisting crustal remanence (for example ∼250 A/m relates to 25% of multi-domain hematite) can trigger a self-magnetizing process that can continue in the absence of magnetic dynamo and continue strengthening and/or weakening magnetic anomalies on Mars. Thickness of the primary magnetic layer and concentration of magnetic carriers allow specification of the temperature gradient required to trigger a self-magnetization process. 相似文献
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Summary The changes of the anisotropy of magnetic susceptibility of igneous rocks, induced by a magnetic field, are studied. It is proved that changes in the degree of anisotropy of susceptibility and of the orientation of the susceptibility ellispoid of specimens occur due to the configuration of the domain structure under the effect of the magnetic field. The influence of this effect on the total anisotropy of rocks depends on the degree of anisotropy due to the shape factor and on the stability of the domain structure. A model concept is presented, explaining the qualitatively different pattern of the changes of the anisotropy of susceptibility under the effect of the magnetic field in various directions of the specimens. 相似文献