共查询到20条相似文献，搜索用时 31 毫秒
1.
D.P. Zidarov 《Physics of the Earth and Planetary Interiors》1985,37(1):74-86
The advantages of the approximation of the Earth's magnetic field by means of the field of the so-called natural magnetic sources are discussed. The shifting of these natural magnetic sources, determined for different epochs, is used to forecast the Earth's magnetic field and to draw conclusions about the motion of the corresponding part of the Earth. On the basis of the representation of the Earth's magnetic field from several past geological epochs as a field of one optimum dipole a new theory about the Earth's evolution is proposed. 相似文献
2.
Edward R. Benton 《Physics of the Earth and Planetary Interiors》1981,24(4):242-244
A simple new method is described for extracting, from magnetic observations taken at Earth's surface, the vertical growth rate of vertical motion, ?u/?r, at special isolated points on the top surface of Earth's liquid core. The technique utilizes only the radial component of the frozen-flux induction equation and it requires information only on the radial magnetic field, Br, its horizontal gradient, and its secular variations, ?Br/?t, at the core-mantle boundary. 相似文献
3.
K. Ramaswamy M. Dheenathayalu S. Bharathan 《Physics of the Earth and Planetary Interiors》1985,40(1):61-64
A detailed study of the ancient intensity of the Earth's magnetic field in Tamilnadu, India is presented using pottery, bricks, tiles etc., obtained from the excavations that have been carried out at some of the important places of historical and archaeological interest. An attempt is made to reconstruct the secular variation of the geomagnetic field intensity. The results reported here reveal considerable changes in the Earth's magnetic field in this region during the past 2400 y. It is observed that the intensity of the geomagnetic field has been previously 57% greater than at present. 相似文献
4.
D. Crossley 《Physics of the Earth and Planetary Interiors》1984,36(1):1-16
There has been renewed interest lately in the possibility that at least a part of the Earth's liquid core may be stably stratified. A gravitationally stable region would permit the existence of inertia-gravity or gravity-inertia waves in addition to the Rossby and Kelvin waves which exist due to rotational effects and which are well known in oceanography and atmospheric dynamics. These wave motions are of interest because their periods are dependent on the density stratification as specified by the buoyancy frequency N which in turn determines the amplitude of large-scale radial motions in the core.The waves have too high a frequency to be connected dynamically to the magnetic field in the core, but if they do exist they may be detectable by sensitive long-period gravimeters at the Earth's surface. This paper examines the available evidence for the frequency regimes, excitation and damping mechanisms of the core waves. It is concluded that although the waves may exist theoretically, their detection and interpretation as a method for determining N is a difficult proposition. 相似文献
5.
Loren Shure Robert L. Parker George E. Backus 《Physics of the Earth and Planetary Interiors》1982,28(3):215-229
Which features of a geomagnetic field model on the surface of the core are really necessary in order to fit, within observational error, the field observations at and above the Earth's surface? To approach this question, we define ‘roughness’ in various ways as a norm on an appropriate Hilbert space of field models which is small when the field is smooth on the core surface. Then, we calculate the model with least norm (the smoothest model) which fits the data, sources outside the core being treated as noise. Sample calculations illustrate the effects of noise, of the choice of norm and of an uneven distribution of observing stations. 相似文献
6.
N.P. Benkova A.N. Khramov T.N. Cherevko N.V. Adam 《Earth and Planetary Science Letters》1973,18(1):141-147
Analytical models of the palaeomagnetic field have been constructed for a number of geological periods (Quaternary Neogene, Jurassic, Triassic, Permian and Permo-Carboniferous) by spherical harmonic analysis using the present-day world map as a basis and (for the earlier periods) using also a palaeogeographic reconstruction. The use of the palaeogeographic chart for the earlier periods simplifies the models, and its use appears to be valid. The low accuracy, small number and uneven distribution of palaeomagnetic data severely limit the conclusions which can be drawn from the analyses. Nevertheless the results for all periods indicate that throughout the past 300 million years the geomagnetic field has maintained its global structure, and has remained similar to the field of a dipole slightly shifted from the Earth's centre. It appears that there have not been any persistent systematic anomalies or variations in the Earth's magnetic field throughout that time, but rather that the field has been oscillating around a mean level not greatly different from that of the present epoch. 相似文献
7.
S.I. Braginsky 《Physics of the Earth and Planetary Interiors》1976,11(3):191-199
A short review of the present state of the nearly axially-symmetrical dynamo model is given. A simplified theory for hydromagnetic dynamos taking into account the forces acting in the Earth's core is considered. The role of weak core-mantle friction is discussed and a form of solution is suggested which is characterized by a large geostrophic velocity in the core and by a boundary layer of a new type. The consequences of such a model (called model Z) for the Earth's dynamo are discussed. 相似文献
8.
R.T. Merrill M.W. McElhinny D.J. Stevenson 《Physics of the Earth and Planetary Interiors》1979,20(2-4):75-82
Paleomagnetic data indicate that there is a north-south asymmetry in the time-averaged magnetic field and that there are small but significant differences between the normal and reverse polarity states. The geographical variation is most likely due to spatial variation in the boundary conditions at the core-mantle interface. The difference in the magnetic fields of the reverse and normal polarity states can be modeled in terms of a “standing field”. The paleomagnetic data are insufficient to determine whether or not this “standing field” is of core origin. However, consideration of mechanisms, including thermoelectric currents, indicates that there probably are important differences in core processes between the two polarity states. At first glance this interpretation is difficult to reconcile with the fact that the magnetic induction equation is antisymmetric with respect to the magnetic field. A way around this problem is the possibility that only certain transitions are allowed between acceptable eigenstates in dynamo models of the Earth's magnetic field. 相似文献
9.
10.
Cedric Wright 《Earth and Planetary Science Letters》1973,19(4):453-460
Seismological results interpreted as evidence for large inhomogeneities near the base of the Earth's mantle below Hawaii have recently been published. It is possible to place constraints on the magnitude of such heterogeneities by identifying seismic phases multiply reflected within the Earth's core. The value of such a simple technique is illustrated by using array recordings of P and S5KP waves that have traversed the bottom of the mantle beneath Hawaii to show that there is no clear evidence for the unusual physical properties attributed to this region of the Earth. Identification of the phase S7KP is also reported. 相似文献
11.
R. Hide 《Physics of the Earth and Planetary Interiors》1985,39(4):297-300
This note summarizes recent studies of atmospheric excitation of short-term changes in the length of the day and polar motion which set useful limits on the timescales associated with angular momentum transfer between the Earth's core and mantle. It also speculates about the nature of the recently-discovered phenomenon of “impulses” or “jerks” in the geomagnetic secular variation, proposing that they might be manifestations of “loop” instability of the magnetic field within the core. Finally, it outlines novel properties of high magnetic Reynolds number flows that bear on the inverse problem of deducing core motions from geomagnetic secular variation data. 相似文献
12.
Siegfried Franck 《Physics of the Earth and Planetary Interiors》1982,27(4):249-254
This paper is concerned with some new problems of the dynamics and energetics of the Earth's core. The model of the so-called gravitationally-powered dynamo is investigated under the assumption of liquid immiscibility in the FeS system as a possible core material. In this way the growing inner core causes nucleation of small FeS-droplets that ascend under the release of gravitational potential energy. This energy is enough to drive a dynamo with a toroidal magnetic field of mean size. 相似文献
13.
M.A. Mayhew 《Earth and Planetary Science Letters》1984,71(2):290-296
Long-wavelength anomalies in the total magnetic field measured by Magsat over the United States and adjacent areas are inverted to an equivalent surface layer magnetization distribution. The model is based on an equal-area dipole grid at the Earth's surface. Model resolution, defined as the closest dipole spacing giving a solution having physical significance, is about 220 km for Magsat data in the elevation range 300–550 km. The magnetization contours correlate well with large-scale tectonic provinces. A higher-resolution (200 km) model based on relatively noise-free synthetic “pseudodata” is also presented. An excellent inverse correlation between apparent magnetization and heat flow in the western U.S. is demonstrated. A new regional heat flow map derived indirectly from Magsat data shows nearly all the important thermal anomalies evidenced in previous published maps. Notably, the map predicts high heat flow in Nebraska and the Dakotas, suggesting the presence of a “blind” geothermal area of regional extent. 相似文献
14.
V. V. Kopeikin 《Geomagnetism and Aeronomy》2011,51(5):676-680
It has been indicated that the electric field that exists above the Earth’s surface contains information about the structure
of underground inhomogeneities. Equations have been obtained and are used to illustrate the numerical calculations of the
electric field strength along the Earth’s surface and some types of underground objects. 相似文献
15.
R.J. Suttill 《Earth and Planetary Science Letters》1980,49(1):132-140
Palaeomagnetic measurements of 1-m cores and a 9-m Delft core of Recent tidal-flat sediments from the Wash, England have shown that these sediments possess a record of the variation of the Earth's magnetic field. The record compares well with the historic-archaeomagnetic record for the period 0–1000 years B.P. but is offset down the core due to the remanence being of post-depositional origin. A period of at least 100 years is suggested for the alignment of particles during acquisition of the post-depositional remanence. Magnetite has been identified as the major carrier of this remanence. 相似文献
16.
D. M. Pechersky A. A. Lyubushin Z. V. Sharonova 《Izvestiya Physics of the Solid Earth》2010,46(7):613-623
The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The
times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized
by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and
the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between
the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic
world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by
the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle
of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes
in the organic world. 相似文献
17.
As the inner core is a good electrical conductor any ambient magnetic field would diffuse into it on a time scale long compared to several thousand years, and conversely be frozen there on shorter time scales. From the observations that the dipole component of the Earth's magnetic field has been inclined persistently to the spin axis over hundreds of thousands of years, and that the dipole drifts and decays significantly more slowly than the nondipole field, it is suggested that the external dipole is simply a manifestation of a field frozen in an inclined inner core. It is shown that the much neglected gravitational restoring torque can be significant for an inclined inner core, so much so that its motion is in the main determined by gravity, with electromagnetic and inertial coupling effects being of secondary importance. A regular precession of the inner core is shown to be possible where its spin axis drifts westward relative to the mantle with a period of ～ 7000 y. Some preliminary calculations of the possible motions of a gravitationally coupled mantle-inner core system are shown. 相似文献
18.
Jupiter's field is strongly dipolar but with relatively large high order moments compared to the Earth's. In situ magnetic field data allow us to interpret most of the Earth-based microwave observations of Jupiter, with the exception of Branson's hot spot. Decametric emissions have a complex rotational pattern which has been stable since 1950; their agreement with the spacecraft magnetic fields is much less satisfactory than that of the microwaves. We conclude that the extrapolation of magnetic fields from the spacecraft to the surface of Jupiter is in error by 40% in the Southern Hemisphere.Saturn's radio emissions show complexities similar to Jupiter's. They are strongly asymmetric about the rotational axis, although Saturn's Field is nearly axisymmetric. Their strong asymmetry suggests strong longitudinal variations in the magnetic field a few thousand kilometers from the cloud tops, in conflict with the field measured aboard Pioneer 11.The magnetic fields within a few thousand kilometers of either Jupiter's or Saturn's cloud tops are probably unknown. It is discouraging that more is not known about the fields after a total of 7 encounters. Perhaps the Galileo probe can test usefully models of the Jupiter field, even if its measurements refer to just one trajectory through the clouds. An arguable case can be made that the giant planets exhibit complexity of magnetic structure similar to the Sun. 相似文献
19.
The magnetic field in the Earth's mantle is computed using a depth-dependent electrical conductivity, of form σ = σa(r/a)?α, and an approximation scheme in which the electromagnetic time constant of the mantle is assumed small compared with the time scales of the secular variation, and in which the induced currents and fields are obtained iteratively. We first associate the toroidal fields in the mantle with motions at the core surface (r = a) which create the observed geomagnetic field by flux rearrangement, and compute the resulting couple, Γ, parallel to the geographical axis. Using only zonal core motions, and values σa = 3 × 103ω?1m?1, α = 30 for the conductivity profile, we find that the toroidal induced fields create a couple, ΓT, that over most of this century has been roughly ten times greater than the poloidal part, ΓS, of Γ, and has the same sign. The total couple, Γ, has fluctuations of order 1018 Nm as required for the observed decade fluctuations in the length of the day. Its average is ～ ?1.5 × 1018 Nm, i.e., it is too large to remain unbalanced. We suppose that an equally important couple in the opposite sense is created by flux leakage from the core, and we estimate the necessary gradient of toroidal field in the core to be of order ?0.5 Gs km?1 at the core surface. During the course of the data analysis needed for the present work, we found some evidence for a torsional wave in the Earth's core with a period of ～ 60 y. 相似文献
20.
B.S. Volvovsky I.S. Volvovsky N.Sh. Kambarov 《Physics of the Earth and Planetary Interiors》1983,31(4):307-312
Deep seismic sounding studies carried out in 1974–79 allowed an important peculiarity of the deep structure of the Pamir-Himalayas region to be established: the thickness of the Earth's crust is almost twice as large here as on the stable plates (65–75 and 35–37 km, respectively). The absence of any evidence for doubling of crustal thickness provides grounds for rejecting the hypothesis of subduction of the rigid Hindustan plate under the geosynclinal folded constructions of the Punjab syntaxis of the Himalayas. The steep inclination of all major faults, dissecting the Earth's crust and often dislocating the M surface, is also counter to this hypothesis. Several faults reflect the dynamics and conditions of formation of deep layers of the lithosphere. For example, the structural seam of the Indus, which has an almost sheer tilt and which penetrates to subcrustal depths, is a channel along which ophiolite associations of crystalline rocks were squeezed from the mantle. The Fore Himalayan and Major Himalayan faults are the boundaries between different structural facial zones. The band of greatest thickness of crust extends within the zone of greatest thickness of the asthenospheric layer; a deep minimum in the Bouguer anomalies (?550 mGal) corresponds to this zone, as does also a depression on the surface of the geoid.Seismicity of the lithosphere of the Pamir-Himalayas region is caused by geodynamic processes manifested in the higher lithospheric layers by block displacements of the Earth's crust (mostly uplifts), and in the lower parts by shifts of the steeply inclined mantle blocks (the Pamir-Hindukush seismic focal zone). 相似文献