Topic
Dipole model of the Earth's magnetic field
About: Dipole model of the Earth's magnetic field is a research topic. Over the lifetime, 2756 publications have been published within this topic receiving 83021 citations.
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TL;DR: In this paper, a new magnetosheath numerical MHD model has been developed which calculates solar wind flow around a paraboloidal obstacle, and the magnetic barrier may almost disappear for a special interplanetary magnetic field orientation nearly aligned with the solar wind velocity.
22 citations
TL;DR: In this article, the authors considered the effect of adding a toroidal field by studying the potential energy perturbation when the rotation is not done along a sharp cut, but with a continuous displacement field that switches the direction of rotation across a region of small but finite width.
Abstract: In 1977, Flowers & Ruderman described a perturbation that destabilizes a purely dipolar magnetic field in a fluid star. They considered the effect of cutting the star in half along a plane containing the symmetry axis and rotating each half by 90 ◦ in opposite directions, which would cause the energy of the magnetic field in the exterior of the star to be greatly reduced, just as it happens with a pair of aligned magnets. We formally solve for the energy of the external magnetic field and check that it decreases monotonically along the entire rotation. We also describe the instability using perturbation theory, and show that it happens due to the work done by the interaction of the magnetic field with surface currents. Finally, we consider the stabilizing effect of adding a toroidal field by studying the potential energy perturbation when the rotation is not done along a sharp cut, but with a continuous displacement field that switches the direction of rotation across a region of small but finite width. Using these results, we estimate the relative strengths of the toroidal and poloidal fields needed to make the star stable to this displacement and show that the energy of the toroidal field required for stabilization is much smaller than the energy of the poloidal field. We also show that, contrary to a common argument, the Flowers–Ruderman instability cannot be applied many times in a row to reduce the external magnetic energy indefinitely.
22 citations
TL;DR: In this paper, the longitudinal invariant of the motion of charged particles trapped in magnetic dipole fields and a compressed dipole field was calculated for the case of an image dipole at a distance 2Z from the dipole axis.
Abstract: The results are given for calculatioan of the longitudinal invariant of the motion of charged particles trapped in a magnetic dipole field and a compressed dipole field. The variation of the longitudinal invariant with the latitude of intersection of the line of force with the earth's surface between 50- and 80 deg was calculated for a dipole field and for a field compressed by an image dipole at a distance 2Z from the dipole axis (Z being the distance from the axis to the front of the charged plane). The results of the calculation are shown graphically to a mirror height of 1000 km. The magnetic field strength is given as a function of the elevation of the mirror point. (B.O.G.)
21 citations
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
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21 citations
TL;DR: In this paper, a classification scheme for cancelling magnetic features according to the origins of their two halves is proposed; the observed properties of flux cancellation are summarized; the cancellation appears to be the observational evidence of magnetic reconnection taking place in or above the photospheric layer.
21 citations