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Showing papers on "Dipole model of the Earth's magnetic field published in 1967"


Journal ArticleDOI
TL;DR: In this paper, a best current model of the main geomagnetic field is presented as a response to a need for an International Geomagnetic Reference Field (IGRF), described by a series of 120 spherical harmonic coefficients and their first and second time derivatives.
Abstract: A best current model of the main geomagnetic field is presented as a response to a need for an “International Geomagnetic Reference Field”. This model is described by a series of 120 spherical harmonic coefficients and their first and second time derivatives from an epoch 1960.0. It was derived from a sample of all magnetic survey data available from the interval 1900-1964 plus a recent global distribution of preliminary total field observations from the OGO-2 (1965-81A) spacecraft for epoch 1965.8. A duplicate data selection was made and the resulting field model compared with the first to help evaluate the minimum error. It was noted that the root —mean—square difference between the two models was about 30γ in the force components, 0.04 degrees in dip and 0.3 degrees in declination at the earth's surface for 1965.0.

278 citations


Journal ArticleDOI
TL;DR: In this paper, the hourly values of the azimuthal component of the interplanetary electric field were related to the different types of magnetic activity observed at a worldwide chain of stations.
Abstract: Hourly average values of solar wind velocity and the components of the interplanetary magnetic field obtained by IMP 1 were combined to obtain the interplanetary electric field as measured in a coordinate system with one axis parallel to the earth's magnetic dipole axis. The hourly values of the azimuthal component of the interplanetary electric field were related to the different types of magnetic activity observed at a worldwide chain of stations. It is found that a positive increment in the azimuthal electric field (enhancement of the southward directed interplanetary magnetic field) is strongly related to the initiation of magnetic bay and storm activity, and that establishment of a negative (or less positive) azimuthal electric field during the course of a storm or bay is associated with the start of the recovery phase. Sudden impulses are shown to be equally often associated with negative and positive increments in the azimuthal electric field and are found to be the most common event observed in this study. The combinations of solar-terrestrial parameters that appear to determine the different types of magnetic activity are discussed in the light of the results presented in this paper.

214 citations


Journal ArticleDOI
07 Jul 1967-Science
TL;DR: Theoretical work on the magnetohydrodynamics of the earth's liquid core indicates that horizontal variations in the properties of the core-mantle interface might nevertheless produce measurable geomagnetic effects and why magnetic astronomical bodies usually rotate.
Abstract: Theoretical work on the magnetohydrodynamics of the earth9s liquid core indicates (a) that horizontal variations in the properties of the core-mantle interface that would escape detection by modern seismological methods might nevertheless produce measurable geomagnetic effects; (b) that the rate of drift, relative to the earth9s surface, of nonaxisymmetric features of the main geomagnetic field might be much faster than the average zonal speed of hydrodynamic motion of core material relative to the surrounding mantle; and (c) why magnetic astronomical bodies usually rotate. Among the consequences of (a) and (b) are the possibilities that (i) the shortest interval of time that can be resolved in paleomagnetic studies of the geocentric axial dipole component of the earth9s magnetic field might be very much longer than the value often assumed by many paleomagnetic workers, (ii) reversals in sign of the geomagnetic dipole might be expected to show some degree of correlation with processes due to motions in the mantle (for example, tectonic activity, polar wandering), and (iii) variations in the length of the day that have hitherto been tentatively attributed to core motions may be due to some other cause.

116 citations


Journal ArticleDOI
TL;DR: In this article, a mathematical model is presented, and a relatively simple solution is obtained that describes the basic characteristics of solar cosmic-ray propagation, and it is demonstrated that the solution of the diffusion equation does apply during the anisotropic phase of several events.
Abstract: A mathematical model is presented, and a relatively simple solution is obtained that describes the basic characteristics of solar cosmic-ray propagation. The model postulates that solar cosmic rays diffuse anisotropically in the interplanetary medium because of the irregular spiral interplanetary magnetic field. It is assumed that the diffusion coefficient along the field direction is constant up to an effective absorbing boundary at r1, where r1 is found to be approximately 2 AU, and that the diffusion coefficient perpendicular to the field lines increases with distance from the sun because of the diminishing magnetic field intensity. The solution of the diffusion equation with these conditions is found to depend significantly on the solar longitude of the flare that produces the cosmic rays. Excellent intensity-versus-time fits are obtained for the events of Feb. 23, 1956; Aug. 22, 1958; May 4, 1960; Sept. 3, 1960; Nov. 15, 1960; Nov. 20, 1960; July 18, 1961; July 20, 1961; Sept. 28, 1961. It is demonstrated that the solution of the diffusion equation does apply during the anisotropic phase of several events. The model is consistent with several east-west effects that have been observed.

115 citations



Journal ArticleDOI
TL;DR: In this paper, the classically reducible problem in magnetogasdynamic steady inviscid flow is applied to the interaction of the solar plasma with planetary magnetic fields, and the results are consistent with Axford's order of magnitude calculation.

70 citations


Journal ArticleDOI
TL;DR: The relationship between the interplanetary magnetic field and the positive-ion component of the solar wind as observed by Mariner 2 was discussed in this paper, showing that the field strength and plasma density were generally much greater than normal at the leading edge of a long-lived high-velocity stream.
Abstract: This paper summarizes some of the relations between the interplanetary magnetic field and the positive-ion component of the solar wind as observed by Mariner 2. Both the field strength and plasma density were generally much greater than normal at the leading edge of a long-lived high-velocity stream. For most of the period of observation, the ratio of magnetic energy density to the energy density of thermal motions of the positive ions was of the order of unity. The Alfven velocity was usually in the range 30–100 km/sec, and, during this period, the solar-wind flow past the earth was always greater than the phase velocity of hydromagnetic waves, a necessary condition for the existence of a hydromagnetic bow shock. The Mariner 2 spectrometer, which always faced the sun, measured the proton velocity dispersion, or temperature, along the solar radius vector. The dependence of this temperature on the instantaneous direction of the magnetic field was inconsistent with the condition T∥ > T⊥ observed by the spherical plasma spectrometers on Pioneer 6 and Vela 3, unless the plasma was much hotter when the interplanetary field was perpendicular than when the field was parallel to the solar radius vector.

62 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the interplanetary magnetic field sector structure, noting Archimedes spiral directivity and 27-day recurrence period for pattern in the magnetic field.
Abstract: Interplanetary magnetic field sector structure, noting Archimedes spiral directivity and 27 day recurrence period for pattern

58 citations


Journal ArticleDOI
TL;DR: In this paper, the cosmic-noise absorption at three locations, ranging in invariant latitude from about 68 to 82°, shows differences that can, at least in one case, be ascribed to differences in the local solar-proton fluxes.
Abstract: Antarctic riometer observations of the PCA event of February 1965 are described. The cosmic-noise absorption at three locations, ranging in invariant latitude from about 68 to 82°, shows differences that can, at least in one case, be ascribed to differences in the local solar-proton fluxes. The observations are consistent with direct measurements of the solar-proton flux and spectrum made by a satellite during the same event, and it is shown that enhancements in proton flux seen by both the satellite and the riometers can be more readily interpreted as spatial variations than as purely temporal variations. Some implications are discussed from the point of view of the propagation of the protons through the interplanetary medium and the connection of the polar-cap field lines to the interplanetary magnetic field.

55 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that for a thin shell there is no change of sign in the drift in conformity with observation, whereas for a (1-1) correspondence with the ones already found for a very thin shell, no such change occurs.
Abstract: Hide (I966) has suggested that the slow westward drift of the non-dipole components of the Earth's magnetic field may be caused by slow free oscillations of the fluid part of the Earth's core in the presence of a dominant toriodal magnetic field. An attempt is made here to analyse this suggestion in detail. First, slow (or second class oscillations in a thin shell are examined in the presence of a uniform toroidal field and Hide's theory is shown to be qualitatively correct but to underestimate the actual periods of oscillation. In these oscillations the drift is to the east and Hide argued that for a thick shell there will be a change of sign in the drift in conformity with observation. Accordingly the present theory is extended to thick shells, but it is shown that, for those oscillations in (1-1) correspondence with the ones already found for a thin shell, no such change of sign occurs. Since such oscillations are as likely to be manifested on the exterior field as any other it is concluded that the analysis presented here raises a serious objection to Hide's proposal. It is noted, however, that for some higher modes of oscillation a drift to the west is almost certain. One of the intriguing properties of the Earth's magnetic field is the slow westward drift of the non-dipole components, with periods of the order of one thousand years. The seat of the Earth's magnetic field is generally believed to be the fluid part of the Earth's core, which lies within a sphere of radius about 3500 km and is believed to lie outside a concentric sphere of radius about 1400 km. On the scale of the phenomenon this fluid may be assumed inviscid and it is generally believed that the magnetic field arises from some form of dynamo action in it (Hide & Roberts I96I). The precise mechanism is still somewhat obscure, however, it having been only established that the dynamo is possible in principle, i.e. that for certain velocity fields in the fluid, there exist non-trivial solutions of Maxwell's equations, everywhere free from singularities. It has not been established yet that such motions are consistent with the Navier-Stokes equations and there is still speculation about the driving mechanism needed to replenish ohmic losses of energy. Granted a dynamo action in the Earth's core, it is reasonable to expect that differential rotation of the fluid will twist the lines of magnetic force sufficiently for the dominant part of the field to be toroidal. For example, in Bullard & Gellman's (I954) model of the earth's magnetic field, the toroidal component is over a hundred times larger than the poloidal component. Such toroidal fields cannot of course be observed directly. In a recent paper Hide (I966) has suggested that the slow westward drift of the non-dipole components of the Earth's field may be caused by free oscillations of a dominant toroidal field modified by the rotation of the fluid in the core. If this field is sufficiently strong for rotational effects to be neglected, then the oscillations are essentially Alfven waves, propagating in opposite directions along

34 citations


Journal ArticleDOI
TL;DR: In this article, the evolution of a magnetic field in a prescribed velocity field is calculated for the idealized case of hexagonal cells, and the results demonstrate the tendency of the field to accumulate at those boundary points where the flow is most strongly converging.
Abstract: Some theoretical models illustrating the growth of magnetic fields around the boundaries of supergranulation cells are given. The evolution of a magnetic field in a prescribed velocity field is calculated for the idealized case of hexagonal cells. The calculations are carried out both for a perfect conductor and a fluid of finite conductivity. The theory is developed in such a way as to be virtually free of specific assumptions about the depth dependence of the supergranulation flow. The results demonstrate the tendency of the field to accumulate at those boundary points where the flow is most strongly converging.


Journal ArticleDOI
01 Jan 1967-Nature
TL;DR: In this paper, the moment of the equivalent dipole of the geomagnetic field (M) can be deduced in terms of the radius of the Earth (a) from the relation of the relation between the Earth's radius and the first three spherical harmonic coefficients.
Abstract: IN the course of an investigation into magnetic secular variation, a number of spherical harmonic analyses were performed on successive 5 year means of results from eighty magnetic observatories. From the first three spherical harmonic coefficients the moment of the equivalent dipole of the geomagnetic field (M) can be deduced in terms of the radius of the Earth (a) from the relation .

Journal ArticleDOI
TL;DR: In this article, a model for the motion of cosmic rays in the interplanetary, electromagnetic field is presented for both isotropic and anisotropic diffusion situations, and measurements of the longterm modulation, including recent high-altitude data obtained in 1965, fit the following simple model.

Journal ArticleDOI
TL;DR: In this article, the average interaction field has been found to be a linear function of the magnetization in agreement with the theoretical predictions of Della Torre, and distribution functions,n(Hi ), have been determined.
Abstract: Interacting systems of a large number of hysteretic bistable magnetic particles have been studied by direct calculation using digital computers. In this paper, we discuss calculations made on oriented dipole moments in a regular cubic array periodically extended parallel to the dipole axes in order to avoid demagnetizationeffects. Distributions of critical fields and moments are assigned to the array. The switching fields of the particles are modified by the interaction field. After the interaction fields are computed, the array is relaxed for the current applied field which may be cycled in any desired variation. The relaxation process is in order of decreasing particle vulnerability. The average interaction field has been found to be a linear function of the magnetization in agreement with the theoretical predictions of Della Torre. Distribution functions,n(Hi ), have been determined. In addition a type of breakdown phenomena in these arrays suggested by Barker has been observed. In application to fine particle systems as used in magnetic recording tapes, effects such as variation in particle orientation and nonuniform dispersions may be simply introduced into a subprogram of the simulation. In a similar fashion the model can be generalized to different types of interactions and applied to other magnetic and dielectriccooperative phenomena.

01 Apr 1967
TL;DR: In this paper, the D-region fair-weather electric field is defined as the equilibrium field produced by the mean circulation of the earth's lower ionosphere through a magnetic field such as the permanent magnetic field.
Abstract: : Motion of a slightly ionized medium such as the earth's lower ionosphere through a magnetic field such as the earth's permanent magnetic field will result in systematic separation of electrical charges. This charge separation will result in development of an opposing electric field which will balance, in the average case, the force produced by the interaction of the motion and the magnetic field. The D-region fair-weather electric field is defined as the equilibrium field produced by the mean circulation. Asymmetries between the earth's geomagnetic and rotational axes and the structure of the stratospheric circulation are considered in determining global and annual structures of the D-region fair-weather electric field. (Author)

Journal ArticleDOI
TL;DR: In this article, it is assumed that during a magnetic storm the earth is situated in a magnetic field whose intensity increases exponentially up to the maximum of the main phase of the storm.
Abstract: It is assumed that during a magnetic storm the earth is situated in a magnetic field whose intensity increases exponentially up to the maximum of the main phase of the storm. The occurrence of a sudden commencement and an initial phase is then explained entirely in terms of currents induced in the ionosphere. In a first model the ionosphere is treated as a spherical layer of uniform conductivity and finite thickness. In a second model only the currents induced in the high conductivity bands at the equator and the auroral zone are considered. The variations in the earth's magnetic field during a magnetic storm calculated by using these models agrees well with the average variations observed at stations with low and middle magnetic latitudes.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the propagation characteristics of e.l.f. electromagnetic waves assuming a perfectly conducting Earth and a sharply-bounded homogeneous ionosphere on which a uniform and radial earth's magnetic field is superposed.

Journal ArticleDOI
TL;DR: A survey of observational and theoretical work pertaining to the origin of planetary magnetic fields is given with special emphasis on the dynamo theory which attempts to explain these fields as arising from magnetohydrodynamic regenerative action as mentioned in this paper.
Abstract: : A survey of observational and theoretical work pertaining to the origin of planetary magnetic fields is given with special emphasis on the dynamo theory which attempts to explain these fields as arising from magnetohydrodynamic regenerative action. Some points are raised regarding what a satisfactory theory should contain. It is suggested that reversals may occur without a drastic change in the internal flow. A method of using one model of dynamo action to obtain information about the structure of the flow in the core of the earth is proposed.

Journal ArticleDOI
K. T. Yen1
TL;DR: In this article, an analytical study of the interaction between the solar wind and the sun's general magnetic field, assumed to be a dipole, is presented, where coupled hydrodynamic and hydromagnetic equations are used to obtain solutions with the property of axial symmetry about the dipole axis.
Abstract: An analytical study of the interaction between the solar wind, assumed to start uniformly from the sun's surface, and the sun's general magnetic field, assumed to be a dipole, is presented. Coupled hydrodynamic and hydromagnetic equations are used to obtain solutions with the property of axial symmetry about the dipole axis. The sun's rotation is not considered. A perturbation analysis is carried out to show how the dipole magnetic field is drawn out by the flow, and how the flow is distorted by the magnetic field. A solution for the interplanetary magnetic field is presented and compared with Parker's curl-free solution. This solution shows the radial component of the magnetic field to be proportional to r~ 2 for large values of r, where r is the radial distance from the sun's center measured in terms of the solar radius. The perturbation of the solar wind by the magnetic field is found to be generally small but different in the subsonic and supersonic regions of the velocity field of the solar wind. In the subsonic region, the solar wind velocity in the polar regions is increased and that near the equator is reduced. In the supersonic region, there is a tendency to reverse this perturbation. I. Introduction I N 1958, Parker1 presented his solar wind theorjr and pointed out that the sun's general magnetic field could be drawn out by the solar wind. Thus the interplanetary magnetic field at the orbit of the earth could be of the order of a few 7?s (17 is equal to 10~5 gauss). Moreover, based on the idea that the magnetic lines are fixed in the sun and rotate with the corona, Parker suggested that the magnetic lines will be in the form of simple Archrinedean Spirals. Recent space measurements2'3 have confirmed both Parker's solar wind theory and his model of the interplanetary magnetic field. So far, the physical process by which the sun's general magnetic field is drawn out has not been studied in any detail. The curl-free magnetic solution obtained by Parker 4 shows that the field strength is of the order of r~2 for large values of r measured in solar radii. However, in Parker's analysis, the solar wind is assumed to concentrate near the sun's equatorial plane as a thin sheet and its only action is to cut off the magnetic lines along the equatorial plane. In the present paper, an analytical study of the interaction between the solar wind and the sun's general magnetic field is made by a perturbation technique. In Fig. 1, the solar wind is shown schematically as starting uniformly from the sun's surface. Since the solar wind is composed of hightemperature plasma, it will interact with the sun's general magnetic field, which is assumed to be dipole-like at the sun's surface. Only the interaction outside of the sun is considered. The magnetic field is not assumed to be curl-free. The purpose is to find not only how the sun's general magnetic field is drawn out by the solar wind, but also how the solar wind is distorted by the action of the magnetic field. The sun's rotation is not considered. Thus, the spiral structure of the interplanetary magnetic field is not obtained. In earlier studies5-6 by the present author, the simpler case of an incompressible "solar wind" was considered. In this paper, these studies are extended to include the compressibility effects of the solar wind.


Journal ArticleDOI
TL;DR: Filamentary interplanetary magnetic field structure effect on solar flare ground observational data was studied in this paper, where the authors showed that solar flares can be associated with solar flares.
Abstract: Filamentary interplanetary magnetic field structure effect on solar flare ground observational data

Journal ArticleDOI
TL;DR: In this article, the magnetohydrodynamic wave equation is derived, and its plane wave solutions are indicated for the case of a radial magnetic field, both axisymmetric and nonaxisymetric solutions are obtained.
Abstract: Resonance of a confined plasma magnetized by a dipole field is a fundamental geophysical problem which, except for special cases, remains unsolved. As an introduction to the equations, formalism, and concepts to be encountered in the more difficult dipole case, the problem of resonance in a plasma magnetized by a monopole or, in general, radial magnetic field has been solved. The magnetohydrodynamic wave equation is derived, and its plane wave solutions are indicated. For the case of a radial magnetic field, both axisymmetric and nonaxisymmetric solutions are obtained. Finally, the concept of vibrating magnetic-field lines is derived and discussed.

Journal ArticleDOI
TL;DR: In this paper, steady and pulsed interactions between moving plasmas and dipole magnetic fields are described and a description of the storm developed from the theory of Chapman and Ferraro rather than from the models of the magnetosphere proposed by Alfven and Karlson is given.

30 Nov 1967
TL;DR: In this article, the authors examined the field structure of dipole transmitters and found that the dipole moment at the transmitter side can be kept constant in the frequency region under consideration, and the sensitivity available on the receiver side is the same for any frequency.
Abstract: : In present report, the field structure of dipole transmitters is examined as dependent on the working frequency. At given technical possibilities and under the condition that the electrical parameters of a homogeneous medium are independent of the frequency, there exists an optimum working frequency for the transversal field component of a magnetic dipole. Given technical possibilities mean that the dipole moment at the transmitter side can be kept constant in the frequency region under consideration, and that the sensitivity available on the receiver side is the same for any frequency. The optimum frequency at typical experimental values of conductivity and dielectric constant lies at 100 kcps. This behavior of field strengths is the same also in the case of an electrical dipole, when considered qualitatively. (Author)


Journal ArticleDOI
TL;DR: In this paper, the average field within a given area is defined as the value of a new field Z M in the center point of the area ΔS, and it is shown that the field thus defined for every point in the measuring plane will be equal to the true field in the point reduced by the fields from the deposits nearest the measurement plane.

Journal ArticleDOI
TL;DR: An exact solution for the vector potential of the disturbance field at the surface of the earth produced by a prolate spheroidal region of enhanced conductivity in the ionospheric Sq current region was found in this article.
Abstract: An exact solution is found for the vector potential of the disturbance field at the surface of the earth produced by a prolate spheroidal region of enhanced conductivity in the ionospheric Sq current region. The ionosphere is treated as homogeneous and infinite in extent. Approximate expressions for the magnetic induction at the surface are derived, and application to the magnetic disturbance produced by a meteor is discussed.

Journal ArticleDOI
TL;DR: In this article, the problem of measuring the magnetic field of stars is outlined, with reference to instrumental requirements Spectrographs and crystals are described, together with techniques of measurement of magnetic fields in sharp-line stellar spectra.