共查询到20条相似文献，搜索用时 46 毫秒
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This article commences by surveying the basic dynamics of Earth's core and their impact on various mechanisms of core-mantle coupling. The physics governing core convection and magnetic field production in the Earth is briefly reviewed. Convection is taken to be a small perturbation from a hydrostatic, “adiabatic reference state” of uniform composition and specific entropy, in which thermodynamic variables depend only on the gravitational potential. The four principal processes coupling the rotation of the mantle to the rotations of the inner and outer cores are analyzed: viscosity, topography, gravity and magnetic field. The gravitational potential of density anomalies in the mantle and inner core creates density differences in the fluid core that greatly exceed those associated with convection. The implications of the resulting “adiabatic torques” on topographic and gravitational coupling are considered. A new approach to the gravitational interaction between the inner core and the mantle, and the associated gravitational oscillations, is presented. Magnetic coupling through torsional waves is studied. A fresh analysis of torsional waves identifies new terms previously overlooked. The magnetic boundary layer on the core-mantle boundary is studied and shown to attenuate the waves significantly. It also hosts relatively high speed flows that influence the angular momentum budget. The magnetic coupling of the solid core to fluid in the tangent cylinder is investigated. Four technical appendices derive, and present solutions of, the torsional wave equation, analyze the associated magnetic boundary layers at the top and bottom of the fluid core, and consider gravitational and magnetic coupling from a more general standpoint. A fifth presents a simple model of the adiabatic reference state. 相似文献
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H. Jochmann 《Surveys in Geophysics》2009,30(1):1-37
Relations to study the influence of geophysical processes on the temporally varying rotation of the Earth are considered.
Liouville’s equations of rotational motion are derived for a two-component Earth model (consisting of a solid mantle and a
fluid core) and suitably simplified for calculations of the influence of mass redistributions on the Earth’s rotational behaviour.
Excitation functions, or effective angular momentum functions, describing the influence of mass redistributions on the equations
of rotational motion are derived, and their calculation is elucidated by some examples. Relations between temporally varying
second degree Stokes coefficients of the gravity field and excitation functions are discussed. Different solutions of the
equations of rotational motion are described. The identification of exciting geophysical processes by the kinematics of the
inverse calculated excitation function is portrayed. 相似文献
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基于PREM模型，利用非自转、球型分层、各向同性、理想弹性（SNREI）地球的形变理论，讨论了地球在不同驱动力作用下的形变特征．采用地球位移场方程的4阶Runge Kutta数值积分方法，解算了在表面负荷和日月引潮力作用下地球表面和内部形变和扰动位，并给出了地球表面的负荷Love数和体潮Love数．结果表明在固体内核中的形变很小，液核中低阶(n＜10)负荷位移随半径的变化非常复杂．当负荷阶数超过10时，地核中的形变和扰动位都很小，地球的响应主要表现为弹性地幔中的径向位移，且随深度增加急剧减弱，负荷阶数越高这种衰减的速度越快．SNREI地球的地表负荷Love数和体潮Love数与信号频率的依赖关系很弱．在计算体潮Love数的过程中，采用了SNREI地球的运动方程，同时考虑了由于地球自转和椭率引起的核幔边界附加压力，这一近似处理方法获得的结果能很好地符合地球表面重力潮汐实际观测结果． 相似文献
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We analyze the present-day data on the periods of free oscillations and amplitudes of the forced nutations of the Earth for evaluating the admissible range of the mass and moment of inertia for the liquid core. The initial model for this study is taken in the form of the model distribution of density and mechanical Q parameters of the mantle suggested in (Molodenskii, 2010; 2011a; 2011b). This model was constructed by the steepest descent method in the space of 64 parameters, which determine the distribution of density and parameters of mechanical Q in the mantle, liquid outer core, and solid inner core of the Earth. We assumed the Q parameter of the mantle and inner solid core to be constant and sought for the density variations for the simplest two-parameter model of the piecewise-linear functions with the jumps on the boundary between the liquid core and the mantle and at the olivine-spinel phase transition at a depth of 670 km in the mantle. After this, the computations were repeated for the other distributions of Q (which were also assumed to be unchanged) that correspond to their limiting admissible values. Using this approach, we managed to find the most probable values of the mass and moment of inertia of the liquid core and determine the admissible range of their values. According to our estimates, the ratios of the mass and moments of inertia of the liquid core to the mass and moment of inertia of the whole Earth fall in the intervals 0.317996 ± 0.00065 and 0.110319 ± 0.00022, respectively. These values are lower than the corresponding values for the PREM model (0.322757 and 0.112297) by (1.48 ± 0.30)% and (1.76 ± 0.35)%, respectively. The interpretation of these results requires the revision and thorough analysis of the data on the admissible temperature range of the liquid core and (or) its chemical composition. 相似文献
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H.H. Schloessin 《Physics of the Earth and Planetary Interiors》1974,9(2):147-156
With the notion that interface and boundary layer phenomena play an important part in those geophysical processes which, by observation appear to be related to the earth's internal boundaries between the solid and liquid phases of its core and mantle, constitutional supercooling suggests itself as a mechanism capable of generating and maintaining inhomogeneities in concentration and density at the boundaries of the liquid core. The mechanism of constitutional supercooling requires a slow overgrowth of mantle and core, and, it implies that this growth process is associated with a selective partitioning of certain impurities shared in different concentrations by the liquid core and the solid phases of mantle and inner core. It can lead to the formation of regular (quasi-periodic) corrugations of the core-mantle and the inner-outer core boundaries with amplitudes of the order of 1 km. Mass redistributions, off-setting continually regenerated concentration and density inhomogeneities, provide a mechanism for core motion in the form of concentration currents. A regular distribution of corrugations or humps may give rise to (zonal) patterns of closed loops of concentration currents either in layers adjacent to the solid-liquid interfaces, or in loops extending through the entire outer core. The development of regular flow patterns should be enhanced if, referable to one particular constituent of the liquid phase, some parts of the solid-liquid interfaces acted as sources, others as sinks. 相似文献
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As is known, the secular deceleration of the Earth's diurnal rotation is explained mainly by the tidal friction in the ocean. Below we consider this mechanism in some detail, taking into account also elastic deformations of the mantle under the action of ocean loading and the interaction between the tide-generating body, ocean tidal wave, liquid outer core, and solid inner core. It is shown that elastic displacements of the core-mantle boundary under the action of ocean loading are of about the same amplitude and phase as the elastic loading displacements of the Earth's outer surface. As a result, side by side with the mechanism of secular deceleration of diurnal rotation of the mantle, there are also (1) the opposite mechanism of secular acceleration of diurnal rotation of the outer liquid core and of the solid inner core and (2) the mechanism of excitation of differential rotation in the liquid core. Taking these effects into account, we compare theoretical and modern observed data on the eastward drift of the solid inner core. It is shown that the best agreement may be obtained if the turbulent viscosity of the liquid core is about 2 × 10
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Poise 相似文献
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Introduction The fluid outer core separates the solid inner core from the solid elastic mantle, and as a result, makes the free and forced movement of this mechanical system more complicated and profuse. As the elastic mantle, the free oscillations may occur within the Earths fluid outer core (FOC) due to excitation of a strong and deep earthquake (Crossley, 1975b; Friedlander, Siegmann, 1982; Shen, 1983; Friedlander, 1985). However, compared with the oscillations of the elastic mantle, i… 相似文献
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S. M. Molodensky 《Izvestiya Physics of the Solid Earth》2008,44(8):615-621
New, unique information on the inertial and dissipative coupling of the liquid core and the mantle has been retrieved from modern high-precision (radiointerferometer and GPS) data on tidal variations in the rotation velocity and nutation of the Earth. Comparison of theoretical and observed data provided new estimates for the dynamic flattening of the outer liquid and the inner solid cores, mantle quality factor, viscosity of the liquid core, and electromagnetic coupling of the liquid core and the mantle [Molodensky, 2004, 2006]. As was shown in the first part of the paper [Molodensky, 2008] (further referred to as [I]), generation of eddy flows in Proudman-Taylor columns, whose orientation is controlled by the topography of the liquid core-mantle boundary, should be taken into account for correct estimation of the inertial coupling (see formulas (8) and (34) in [I]). The range of periods within which this effect plays a significant role is determined by the decay time of these flows. This time is estimated in the paper for the case where dissipation is related to viscous friction at the core-mantle boundary or with the electromagnetic coupling of the liquid core and the mantle. Because of significant uncertainties in modern data on the viscosity of the liquid core, the magnetic field intensity at the core-mantle boundary, and the electrical conductivity of the lower mantle, the dissipative coupling of the liquid core and the mantle cannot be calculated as yet. However, as shown in the paper, the decay time of eddy flows is connected with the attenuation time of subdiurnal free nutation and with the liquid core viscosity. This enables the estimation of the frequency dependence of the dissipative coupling in a fairly wide range. It is shown that the range of periods for which relations (8) and (34) in [I] are valid encompasses the best-studied length-of-day variations and, therefore, these relations are applicable to analysis of the majority of modern data. 相似文献
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本文在小扰动条件下,从粘性可压缩流体的运动方程、状态方程以及连续性方程导出了它的波动方程,从而表明粘性可压缩流体中能够存在有耗损的纵波与横波。文中还针对自由界面、刚性界面、粘性流体内部分界面、粘性流体与弹性固体分界面等,求出了平面波的反射系数和透射系数。 相似文献
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地球固体内核（SIC）和地球其余部分之间的引力和压力的耦合作用引起了一个力矩，从而对地球的章动运动产生影响.由于SIC的转动惯量和整体地球转动惯量相比是非常小的，因此可以认为SIC的动力学效应只是导致一个新的章动本征模，其频率与自由核章动（FCN）相差不太远，且对地球章动产生了一个微弱的共振影响.本文在文献〔1〕理论的基础上，对内核地球自转动力学理论进行了更加深入和详细的研究，顾及到高阶引潮力位的影响，介绍了研究内核地球自转的基本假设和定义，引潮力位的复数球函数表示，复数矢量球函数的基本理论等. 相似文献
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K. D. Aldridge J. Bloxham V. Dehant D. Gubbins R. Hide J. Hinderer K. A. Hutcheson D. Jault C. A. Jones H. Legros J. -L. Le Mouël D. Lloyd J. M. Wahr K. A. Whaler K. Zhang 《Surveys in Geophysics》1990,11(4):329-353
Several aspects of core-mantle interactions were considered during a Royal Astronomical Society Discussion Meeting on 12th May 1989, including modelling the geomagnetic field at the core surface, the morphology of the field between 1600 and 1820 AD, dynamo theory, Taylor's constraint, fluid motions at the top of the core that reproduce the observed secular variation, pressure coupling between the core and mantle and its geophysical consequences, topographic core-mantle coupling, angular momentum transfer at the core-mantle interface, the detection and implications of core oscillations, particularly those with associated fluctuations in the Earth's rotation rate, and the seismological determination of the core-mantle boundary topography from lateral inhomogeneities in the mantle. 相似文献
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A study is made of the thermal and compositional conditions which the liquid outer core must satisfy at the inner core boundary, assuming the inner core to be growing by continual solidification of the heavy component of the liquid alloy in the outer core. It is found that the outer core is strongly destabilized by the compositional gradients driven by the separation process associated with the freezing. Further, it is argued that all the freezing necessary for the growth of the solid inner core cannot occur on a flat interface; most of it must occur above the solid boundary in a region labeled the slurry layer. 相似文献
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A multi-layered kinematic dynamo model: implications of a stratified upper layer in the Earth's core
It has been suggested that there exists a stably stratified electrically conducting layer at the top of the Earth's outer fluid core and that lateral temperature gradients in the lower mantle is capable of a driving thermal-wind-type flow near the core–mantle boundary. We investigate how such a flow in a stable layer could influence the geomagnetic field and the geodynamo using a very simple two-dimensional kinematic dynamo model in Cartesian geometry. The dynamo has four layers representing the inner core, convecting lower outer core, stable upper core, and insulating mantle. An α2 dynamo operates in the convecting outer core and a horizontal shear flow is imposed in the stable layer. Exact dynamo solutions are obtained for a range of parameters, including different conductivities for the stable layer and inner core. This allows us to connect our solutions with known, simpler solutions of a single-layer α2 dynamo, and thereby assess the effects of the extra layers. We confirm earlier results that a stable, static layer can enhance dynamo action. We find that shear flows produce dynamo wave solutions with a different spatial structure from the steady α2 dynamos solutions. The stable layer controls the behavior of the dynamo system through the interface conditions, providing a new means whereby lateral variations on the boundary can influence the geomagnetic field. 相似文献
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Steven D. London 《地球物理与天体物理流体动力学》2013,107(5):397-411
The equations for an electrically conducting fluid in cylindrical coordinates are linearized assuming that the inertial terms in the momentum equation can be ignored (small Rossby number), and that the ratio of the Elsasser number and magnetic Reynolds number is one. After these assumptions, the governing equations are linearized about an ambient solution which vanishes at the the equator. Upon assuming large Elsasser and magnetic Reynolds number, the solutions to the linearized equations are approximated by wave trains having very short wave length (relative to the core radius) but which vary slowly (on a scale of the core radius). The period of the waves is much longer than a day but much shorter than the period of the slow hydromagnetic oscillations. These waves are found to be trapped in a region about the equator and away from the axis of rotation. The waves break at a latitudinal wave region boundary, in the sense that the waves become exponentially large in a boundary layer, having as an exponent some positive power of the large azimuthal wave number. This behavior is amplified as the Elsasser number becomes smaller while still remaining relatively large. Waves in more Earth-like parameter regimes are discussed briefly. 相似文献
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The equations of motion of a rotor finite element subjected to six components of base excitation are developed by applying variational principles. The equations contain speed dependent gyroscopic terms, base rotation dependent parametric terms and several forcing function terms which depend upon the linear accelerations, rotational accelerations and a combination of linear and rotational velocities. To evaluate the importance of various terms, seismic response characteristics of a rotating machine subjected to simulated base excitations are studied. It is observed that even for strong rotational inputs the parametric terms in the equation of motion can be ignored without affecting the response. The rotational input terms in the forcing function, however, are quite important and can be ignored only when they are not very strong. Since the problematic parametric terms can be ignored, one can use a generalied modal analysis approach. 相似文献
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All the finite strain equations that we are aware of that are worth considering in connection with the interior of the Earth are given, with the assumptions on which they are based and corresponding relationships for incompressibility and its pressure derivatives in terms of density. In several cases, equations which have been presented as new or independent are shown to be particular examples of more general equations that are already familiar. Relationships for deriving finite strain equations from atomic potential functions or vice versa are given and, in particular it is pointed out that the Birch-Murnaghan formulation implies a sum of power law potentials with even powers. All the equations that survive simple plausibility tests are fitted to the lower mantle and outer core data for the PEM earth model. For this purpose the model data are extrapolated to zero temperature, using the Mie-Grüneisen equation to subtract the thermal pressure (at fixed density) and the pressure derivative of this equation to substract the thermal component of incompressibility. Fitting of finite strain equations to such zero temperature data is less ambiguous than fitting raw earth model data and leads immediately to estimates of the low temperature zero pressure parameters of earth materials. On this basis, using the best fitting equations and constraining core temperature to give an extrapolated incompressibilityK
0=1.6×1011Pa, compatible with a plausible iron alloy, the following numerical data are obtained: Core-mantle boundary temperature 3770 K Zero pressure, zero temperature densities: lower mantle 4190 kg m–3 outer core (solidified) 7500 kg m–3 Zero pressure, zero temperature incompressibility of the lower mantle 2.36×1011PaHowever, an inconsistency is apparent betweenP() andK() data, indicating that, even in the PEM model, in which the lower mantle is represented by a single set of parameters, it is not perfectly homogeneous with respect to composition and phase. 相似文献