Showing papers on "Dipole model of the Earth's magnetic field published in 1969"

A model of interplanetary and coronal magnetic fields.

Abstract: Green function solution to Maxwell equations for interplanetary and coronal magnetic fields above photosphere, considering field at source surface

Quantitative models of the magnetosphere.

Abstract: Quantitative magnetic field models of magnetosphere for analyzing field configuration variations and adiabatic particle motion

A theory for the interpretation of lunar surface magnetometer data

Abstract: The solution to the problem of the motion of the Moon relative to spatial irregularities in the interplanetary magnetic field is found. The lunar electrical conductivity is modeled by a two-layer conductivity profile. For the interaction of the Moon with the corotating sector structure of the interplanetary magnetic field it is found that the magnetic field in the lunar shell is the superposition of an oscillatory uniform field, an oscillatory dipole field and anoscillatory field that is toroidal about the axis of the motional electric field. With various lunar conductivity models and the theory of this paper, lunar surface magnetometer data can be quantitatively interpreted to yield information on the conductivity and consequently the temperature of the lunar core.

Response of the Moon to the time-varying interplanetary magnetic field

Abstract: The solar wind plasma on the sunlit side of the moon is apparently energetic enough to confine any lunar magnetic fields within the lunar surface. Accordingly, the effect of the confining solar wind currents is represented by imposing a surface current at the moon-solar wind boundary, and the induced magnetic field in the lunar interior is calculated as a function of frequency for a simple core-crust model. The solution provides a method for estimating the electrical conductivity, and thus for obtaining information on the temperature, of the lunar interior from magnetic field measurements at the lunar surface.

Solar Source of Interplanetary Magnetic Fields

Abstract: Solar mean magnetic field relation to sector structure of interplanetary magnetic field, discussing Explorer 33 and 35 observations

Dipole model of the sources of the Earth's magnetic field and secular change

Abstract: The magnitude, colatitude, longitude, and distance from the center for radial dipoles were adjusted by a least-squares procedure so as to reproduce the surface magnetic field synthesized from the Fineh-Leaton (F.L.) 1955 Spherical Harmonic Coefficients and for the 1965 International Geomagnetic Reference Field (IGRF). The rms residual was reduced to 28 γ using 21 dipoles for the 1955 field (6th degree and order) and to 25 γ using 35 dipoles for the IGRF (8th degree and order). These residuals include all components of the surface field. The dipole parameters were then varied using a least-squares method to approximate the secular change field. These solutions match the Z component of secular change field synthesized from Leaton's 1955 coefficients to a rms residual of 2.15 γ per year and the IGRF secular change field to a rms residual of 1.26 γ per year. In both cases the dipole sources were found to be approximately 0.2 earth radius from the center of the earth.

Time‐dependent lunar electric and magnetic fields induced by a spatially varying interplanetary magnetic field

Abstract: Homogeneous conducting moon-solar wind interactions, describing time dependent lunar magnetic and electric fields induced by interplanetary magnetic field variations

MORPHOLOGY OF OUTER RADIATION ZONE ELECTRON (E > 35 keV) ACCELERATION MECHANISMS.

Abstract: A study of outer radiation zone electron intensities at times of magnetic storms is reported. The purpose of the study is to determine how well the intensity at one local time tracks the intensity at the same invariant latitude but at a different local time. Any difference in the intensity time profiles might be expected to yield information about the mechanisms responsible for acceleration of outer-zone electrons, particularly the locations of these mechanisms. The measurements refer to selected periods of several days each and have been obtained at altitudes below 3500 km, invariant latitudes in the range 50° to 72°, and at several pairs of local times. At times of magnetic storms the tracking at the two local times is often quite poor at latitudes as low as 55°. For short periods around local midnight and on the morning side of the earth the intensities observed are appreciably higher than those on the afternoon side. It is concluded from these observations that most of the storm-time acceleration of electrons to energies about 35 kev takes place on the night and morning sides of the earth. The measurements are used to place an upper limit on stably trapped fluxes in the outer radiation zone that agrees reasonably well with the whistler mode limiting flux calculated by Kennel and Petschek [1966].

About the influence of inhomogeneities of magnetic fields on line contours and magnetographic measurements

Abstract: The discrepancies between theoretical and experimental calibration curves for solar magnetographs (Severny, 1967) may be explained by horizontal inhomogeneities of the observed but not resolved magnetic field region. Using the Unno solution of the equations of transfer simple two-stream models have been constructed. For the more complicated case of a depth dependence of the magnetic field vector it is shown assuming pure absorption and permitting arbitrary variations of the magnetic field vector and the atmosphere model with depth that a solution of the equations of transfer may be found by iteration.

A dipole approximating to the highest possible degree the earth's magnetic field

Abstract: The coordinates and the components of the dipole approximating to the highest possible degree the earth's magnetic field are determined minimizing a sum of squares of differences between the dipole field and the earth's magnetic field. Numerical results by the aid of a digital computer have been obtained for epoch 1932, 1937, 1942, 1945, 1950, 1955 and 1960 on the basis of magnetic data from 61 observatories.

Hydromagnetic radiation from electric and magnetic dipoles in the magnetosphere.

Abstract: This paper deals with the radiation characteristics of elementary electric and magnetic dipoles in a homogeneous, anisotropic, cold plasma of infinite extent with a uniform magnetostatic field. The cases treated include the electromagnetic sources taken parallel and perpendicular to the magnetostatic field. In all cases expressions for the field components are obtained which are valid at frequencies well below the ion cyclotron frequency. It is found that electric and magnetic dipole sources when oriented perpendicular to the magnetic field excite both ordinary and extraordinary modes. For the ordinary mode, the waves are guided in both directions within cones of small apex angle aligned with the static field. When the dipole sources are aligned with the magnetic field, it is found that the electric dipole excites only the ordinary mode leading to guided wave propagation, while the magnetic dipole excites only the extraordinary mode. In all cases the waves propagate at Alfven speed. The radiation characte...

Solar-wind model including the effects of rotation, magnetic fields, and anisotropic heat conduction.

Abstract: A time-independent solar-wind model is considered in the case of spherical symmetry and of radial magnetic field at the sun’s surface. The energy equation includes besides the usual terms also the heat conduction and magnetic-energy convection (Poynting vector) terms. The dependence of the thermal conductivity on the magnetic field is taken into account. Numerical integrations of the basic equations were performed under the following assumptions: (i) close to the sun the magnetic field is the dominant azimuthal term and solid-body rotation is enforced; (ii) beyond the Alfvenic point the terms quadratic in B are neglected. The model leads to azimuthal velocity at earth between 0.6 and 2.7 km/sec, to radial velocity at earth between 350 and 500 km/sec, and to angular momentum loss of 5 × 1018 cm2/sec per unit mass of gas leaving the solar equator. The dependence of the solutions on the reduction of the effective thermal conductivity caused by the micro-structures in the solar wind suggests that the conditions at earth may be largely determined by a transition region in the solar wind, in which the conduction regime changes into an almost adiabatic flow.

Bearing Deviation in High‐Frequency Transionospheric Propagation: 3. Ray Tracing Investigation of the Magnetoionic Effect

Abstract: The influence of an earth-centered dipole magnetic field upon the bearing deviation of medium range HF ray paths in the ionosphere is investigated by using the ESSA three-dimensional computer ray tracing program for a variety of conditions involving quasi-parabolic layer models and actual electron density profiles deduced from ionograms gathered during a direction finding experiment. The adequacy of the dipole model is examined by comparing the bearing deviations obtained from it with those for a magnetic field based upon spherical harmonic expansion using Gaussian coefficients.

History of the geomagnetic field

Abstract: Direct measurements of the direction and strength of the earth's magnetic field have provided a knowledge of the field's form and behavior during the last few hundreds of years For older times, however, it has been necessary to measure the magnetism of certain rocks to learn what the geomagnetic field was like For example, when a lava flow solidifies (at temperatures near 1000°C) and cools through the Curie point of the magnetic minerals contained in it (around 500°C) it acquires a remanent magnetism that is (1) very weak, (2) very stablel, (3) paralle to the direction of the ambient geomagnetic field, and (4) proportional in intensity to the ambient field Separating, by various analytical means, this magnetization from other ``unwanted'' magnetizations has allowed paleomagnetists to study the historical and prehistorical behavior of the earth's field It has been learned, for example, that the strength of the field was almost twice its present value 2000 years ago and that it has often completely reversed its polarity Paleo‐magnetists have also confirmed that most oceans are, geologically speaking, relatively new features, and that the continents have markedly changed their positions over the surface of the earth

Discussion of paper by J. L. Blank and W. R. Sill, ‘Response of the Moon to the time‐varying interplanetary magnetic field’

Abstract: Critique of magnetic response model for interaction of moon and interplanetary plasma magnetic field proposed by Blank and Sill

Magnetohydrodynamic disturbances in the earth's core, IV

Abstract: In Paper III (Mohandis [1]2) we considered the sudden introduction of amagnetic dipole in the earth's core to act as a source of disturbance to the exitation field taken as a poloidal one. A symmetrical case was considered where the dipole axis is placed parallel to the original field and perpendicular to the earth's mantle. In the present work, we consider an unsymmetric case where the axis of themagnetic dipole is placed perpendicular to both the mantle and the exitation field which is taken as a toroidal one. A mathematical study is made for the resulting fluid motion in the core as well as for the generated hydromagnetic perturbations in both the mantle and the earth's fluid core. A more powerful method has been adopted than those used in previous cases.

Lunar s urface m agnetometer d ata

Abstract: The solution to the problem of the motion of the Moon relative to spatial irregularities in the interplanetary magnetic field is found. The lunar electrical conductivity is modeled by a two- layer conductivity profile. For the interaction of the Moon with the corotating sector structure of the interplanetary magnetic field it is found that the magnetic field in the lunar shell is the super- position of an oscillatory uniform field, an oscillatory dipole field and an oscillatory fieM that is toroidal about the axis of the motionat electric field. With various lunar conductivity models and the theory of this paper, lunar surface magnetometer data can be quantitatively interpreted to yield information on the conductivity and consequently the temperature of the lunar core. The electromagnetic interaction of the Moon and the solar wind plasma has been considered by several authors. Sonett and Colburn (1967, 1968) described the steady state electromagnetic interaction of a Moon with electrical conductivity a moving with velocity v relative to a constant magnetic field B in terms of a unipolar generator. For an infinitely conducting plasma, an observer moving with the Moon would measure a magnetic field B and an electric field v x B in the solar wind. The electric field within the homogeneous Moon is everywhere the motional field v x B. Thus currents, whose density is av x B, flow in the lunar interior and produce an induced magnetic field which is toroidal with respect to the direction of the motional electric field. Currents at the Moon-plasma boundary provide for the completion of closed current paths. Hollweg (1968) has applied this steady state solution to a Moon with a two-layer electrical conductivity model, i.e. a core of constant electrical conductivity a c surrounded by a shell of constant electrical conductivity a s. The two-layer con- ductivity model provides a simple method of accounting for the possibility that the lunar electrical conductivity may change by several orders of magnitude between the Moon's surface and its interior (England et al., 1968). The quasi-periodic sector structure of the interplanetary magnetic field necessitates consideration of the time-dependent electromagnetic interaction problem. The relative motion of the Moon with respect to spatial irregularities in the incident interplanetary magnetic field produces time-dependent electric and magnetic field fluctuations in the * Presently visiting the Max-Planck-Institut ffir Physik und Astrophysik, Mfinchen, Germany.

Magnetic sample-and-hold damping of a gravity-gradient stabilized satellite.

Abstract: : Sample-and-hold magnetic damping provides a method using the earth's magnetic field for libration damping. A spacecraft-fixed magnetic dipole initially parallel to the earth's magnetic field vector is generated and held constant as the satellite rotates. When the magnet is turned off, a portion of the libration energy is transferred to the earth's magnetic field. A mathematical model of this system is developed for a satellite in a near synchronous equatorial orbit. The DODGE satellite libration during the last quarter of 1967 is compared with its theoretical motion in a time-varying magnetic field. The results indicate that a possible cause of the large attitude motion was the dipole-magnetic field interaction which was near resonance with normal modes of the motion. A criterion is developed for operating the system in closed-loop fashion to insure continuous libration damping. An included example uses actual DODGE attitude data. (Author)

Spherical Harmonic Analysis of the Earth's Magnetic Field, Applied to a Limited Part of the World

Abstract: To study the regional effects of the secular variation of the Earth's magnetic field, it is shown that the normal field in a region may be expressed as a limited development in spherical functions. The formulae obtained would be directly comparable from one region to another as well as for the geomagnetic field. As an example, the field has been calculated in France since 1948. Emphasis has been particularly put on the calculation of the precision obtained on the Gauss coefficients.