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Abstract The magnetic Reynolds number (MRN) is used in estimating the quantities appearing in the current theory of the nearly symmetric dynamo. In kinematic theory, all expansions can be developed in terms of the MRN, but this seems to be less advantageous in the case of hydromagnetic theory and in particular the model-Z. An attempt has been made to replace the role of the MRN in the nearly symmetric expansion by the amplitudes of the individual quantities, where the amplitudes of the non-axisymmetric quantities are considered to be small compared with those of the azimuthal quantities. The amplitude of the axially asymmetric velocities and the amplitude of Archimedean buoyancey play essential roles here. The expansions of the theory are valid only when certain assumptions are made about the field amplitude, and the velocity and buoyancy forces, even though the amplitude of the resulting a-effect is unaffected. The a-effect can be altered only by rapid changes in the non-symmetric velocities in the generation region. 相似文献
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Alexander P. Anufriev Ivan Cupal Reviewer G. Siráň 《Studia Geophysica et Geodaetica》1987,31(1):37-42
Summary The behaviour of the poloidal and toroidal magnetic field at the core-mantle boundary is analysed in more detail, assuming that the conductive layer in the lowest mantle is thin. We can conclude that, in the case of the Z-model of the nearly symmetric hydromagnetic dynamo, the poloidal field may be considered potential everywhere in the mantle and that the azimuthal field depends on the geostrophic azimuthal velocity in the same manner as derived in[1] and[3].
aau ¶rt;-amu n¶rt;nuu m n¶rt; amuu aauum n¶rt;u nu¶rt;a u mu¶rt;a n. am ¶rt;, m Z-¶rt;u nmu umuu¶rt;aum ¶rt;ua aum nu¶rt;a n umam nmua ¶rt; amuu a n¶rt;u . ¶rt;m¶rt;am na [1] u [3] auum auma aum n m auma mu.相似文献
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Ferromanganese nodules of the Baltic Sea: Composition,helium isotopes,and growth rate 总被引：1，自引：0，他引：1
Results of the study of shallow-water ferromanganese nodules in the Gulf of Finland of the Baltic Sea, which are of practical interest for metallurgical and chemical industries, are discussed. The nodules contain the following elements: Mn, Fe, Si, Al, Na, Mg, Ti, K, V, Cu, Ni, Zn, P, and Ba. Contents of Mn (～30%) and Fe (～10%) are virtually similar to those in deep-sea oceanic nodules. However, concentrations of Ti, Cu, and Ni are notably lower than average values in oceanic nodules. The helium isotopic composition was studied to reveal cosmic dust in the nodule substance. The measured 3He and 4He concentrations are ～10?12 and ～10?5 cm3/g, respectively. The isotope ratio 3He/4He is approximately 10?7. More than 60% 3He is of cosmic (solar) origin, whereas 4He is of terrigenous (radiogenic) origin. Based on the cosmic duct concentration and the space tracer method, the FMN growth rate is estimated at 8–9 mm/ka at the nodule age varying from ～800 to 1500 yr. The growth rate of nodule has negative correlation with its size. Based on literature data, the growth rate of FMN from the western Baltic Sea is twice as high. An independent calculation of the FMN growth rate based on the diffusion-sorption mechanism (DSM) yielded 8.1 mm/ka, which is very close to the result based on the space tracer method. This value is proposed as the average growth rate of the studied nodules. Comparison with our previous measurements of growth rates for oceanic nodules showed that these values differ only slightly and are equal to n mm/ka, where n < 10. It is inferred that the formation mechanism of both marine and oceanic nodules is based on the same principles that control the generation of mobile forms of Mn in the bottom layer of sediments, i.e., principles related to bioproductivity of sea and ocean basins. Fluxes of lithogenic forms of Mn are of minor importance. 相似文献
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A. P. Anufriev 《地球物理与天体物理流体动力学》2013,107(1-4):269-273
Abstract Latitude behavior of the boundary α-effect based on reflection of hydromagnetic waves from the Core-Mantle Boundary (CMB) studied earlier by Anufriev (1991), is discussed. Its form given in Figure 2 is in good agreement with that used in model-Z of Braginsky. We want to emphasize the following main features of our α-effect which resemble those of Braginsky: concentration near the boundary, sign-changing of α in the layer and geometrical behavior. The last includes the vanishing of α near the poles and the equator which is characteristic for Braginsky's α-effect. It is also shown that for Magnetic Reynolds Number of order 100 the amplitude of the α-effect and the thickness of the α-layer is of the order of those used in model-Z. 相似文献
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This contribution is aimed at a comparison of two different methods of how to deal with the solid inner core in geodynamo models. The first method, based on a direct application of the non-slip boundary conditions, was frequently used in the past. The second one, developed by the authors of the present paper, is based on an advanced analytical solution within the boundary layers and consequent formulation of new boundary conditions on the flow in the volume of the outer core. As an example we have used the results obtained by Hollerbach (1997) in the study of the influence of an imposed axial magnetic field on the fluid flow in a differentially rotating spherical shell. In the case of a weak imposed magnetic field, our solutions are very similar to those of Hollerbach. This non-trivial correspondence confirms the correctness of both methods, which are different not only in the formulation of boundary conditions, but also in the numerical methods: whereas Hollerbach used spectral methods, our computer code is based on finite differences. The influence of the conductivity of the inner core on the fluid flow was also studied. 相似文献
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G. S. Anufriev 《Geomagnetism and Aeronomy》2014,54(6):680-687
A reconstruction of data on ancient (to ～600 Ma ago) solar fluxes of protons and helium has been performed on the basis of isotopic investigations of helium and neon in lunar soil samples from columns delivered by the automatic stations Luna-16 and Luna-24 in 1970 and 1976. Recent investigations have shown the presence of long-term climate variations, which can be explained in the context of solar-terrestrial links. However, the “space” impact, simultaneously with the Sun’s influence on the Earth, takes place in the form of cosmic ray irradiation and as an influence on the Earth that is exerted by the flux of cosmic dust and meteorites (including the very large ones at the early stage of the Earth evolution). Therefore the existence of long-term variability of solar corpuscular fluxes may serve as direct evidence of the manifestation of solar-terrestrial links. The possibility of finding these links appears on the basis of the revealed variations of solar wind fluxes with an age from the contemporary level to the level of ～600 Ma ago. 相似文献