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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: The NMR of the Earth's magnetic field is used for diffusion-weighted imaging of phantoms and it turns out that the expression for spin echo attenuation is identical to the well-known Torrey formula only when the applied nonuniform field has a proper symmetry.
31 citations
TL;DR: In this article, simulations of the initial expansion of a plasma injected into a stationary magnetized background plasma in the presence of a dipole magnetic field are carried out in two dimensions with a kinetic ion, massless fluid electron (hybrid) electromagnetic code.
Abstract: Simulations of the initial expansion of a plasma injected into a stationary magnetized background plasma in the presence of a dipole magnetic field are carried out in two dimensions with a kinetic ion, massless fluid electron (hybrid) electromagnetic code. For small values of the magnetic dipole, the injected ions have large gyroradii compared to the scale length of the dipole field and are essentially unmagnetized. As a result, these ions expand, excluding the ambient magnetic field and plasma to form a diamagnetic cavity. However, for stronger magnetic dipoles, the ratio of the gyroradii of the injected ions to the dipole field scale length is small so that they remain magnetized, and hence trapped in the dipole field, as they expand. The trapping and expansion then lead to additional plasma currents and resulting magnetic fields that not only exclude the background field but also interact with the dipole field in a more complex manner that stretches the closed dipole field lines. A criterion to distinguish between the two regimes is derived and is then briefly discussed in the context of applying the results to the plasma sail scheme for the propulsion of small spacecraft in the solar wind.
31 citations
TL;DR: The scaling properties of the interplanetary magnetic field magnitude show solar cycle variation that can be distinguished in the scaling exponents revealed by structure functions in hydrodynamic turbulence as discussed by the authors.
Abstract: Interplanetary magnetic field magnitude fluctuations are notoriously more intermittent than velocity fluctuations in both fast and slow wind. This behavior has been interpreted in terms of the anomalous scaling observed in passive scalars in fully developed hydrodynamic turbulence. In this paper, the strong intermittent nature of the interplanetary magnetic field is briefly discussed comparing results performed during different phases of the solar cycle. The scaling properties of the interplanetary magnetic field magnitude show solar cycle variation that can be distinguished in the scaling exponents revealed by structure functions. The scaling exponents observed around the solar maximum coincide, within the errors, to those measured for passive scalars in hydrodynamic turbulence. However, it is also found that the values are not universal in the sense that the solar cycle variation may be reflected in dependence on the structure of the velocity field.
31 citations
TL;DR: It is argued that a "stratification" of magnetic sources exists in the fluid core such that the axial dipole is the only observed field component that is nearly immune from the influence exerted by the lowermost mantle.
Abstract: We present evidence that the source of Earth's axial dipole field is largely independent from the sources responsible for the rest of the geomagnetic field, the so-called nonaxial dipole (NAD) field. Support for this claim comes from correlations between the structure of the historic field and the behavior of the paleomagnetic field recorded in precisely dated lavas at those times when the axial dipole was especially weak or nearly absent. It is argued that a "stratification" of magnetic sources exists in the fluid core such that the axial dipole is the only observed field component that is nearly immune from the influence exerted by the lowermost mantle. It follows that subsequent work on spherical harmonic-based field descriptions may now incorporate an understanding of a dichotomy of spatial-temporal dynamo processes.
31 citations
TL;DR: In this paper, 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).
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.
31 citations