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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 evolution of the photospheric magnetic field pattern over eleven solar rotations preceding a minimum of the activity cycle is characterized by abrupt changes of the dominant geometrical patterns of the field as mentioned in this paper.
Abstract: The evolution of the photospheric magnetic field pattern over eleven solar rotations preceding a minimum of the activity cycle is shown to be characterized by abrupt changes of the dominant geometrical patterns of the field. These changes are associated with the onset and end of a sudden increase in the calculated total energy content of the field, which is otherwise decreasing through the period. The calculated geometrical rearrangements correspond in time to observed restructurings of the corona, the interplanetary field, and the solar rotation pattern.

20 citations

Journal ArticleDOI
TL;DR: A review of the concepts and main results of planetary dynamo modeling, contrasting them with the solar dynamo, can be found in this paper, where the authors give an overview on the fundamental properties of planetary magnetism.
Abstract: Direct numerical simulations of the geodynamo and other planetary dynamos have been successful in reproducing the observed magnetic fields. We first give an overview on the fundamental properties of planetary magnetism. We review the concepts and main results of planetary dynamo modeling, contrasting them with the solar dynamo. In planetary dynamos the density stratification plays no major role and the magnetic Reynolds number is low enough to allow a direct simulation of the magnetic induction process using microscopic values of the magnetic diffusivity. The small-scale turbulence of the flow cannot be resolved and is suppressed by assuming a viscosity far in excess of the microscopic value. Systematic parameter studies lead to scaling laws for the magnetic field strength or the flow velocity that are independent of viscosity, indicating that the models are in the same dynamical regime as the flow in planetary cores. Helical flow in convection columns that are aligned with the rotation axis play an important role for magnetic field generation and forms the basis for a macroscopic α-effect. Depending on the importance of inertial forces relative to rotational forces, either dynamos with a dominant axial dipole or with a small-scale multipolar magnetic field are found. Earth is predicted to lie close to the transition point between both classes, which may explain why the dipole undergoes reversals. Some models fit the properties of the geomagnetic field in terms of spatial power spectra, magnetic field morphology and details of the reversal behavior remarkably well. Magnetic field strength in the dipolar dynamo regime is controlled by the available power and found to be independent of rotation rate. Predictions for the dipole moment agree well with the observed field strength of Earth and Jupiter and moderately well for other planets. Dedicated dynamo models for Mercury, Saturn, Uranus and Neptune, which assume stably stratified layers above or below the dynamo region, can explain some of the unusual field properties of these planets.

20 citations

Journal ArticleDOI
TL;DR: In this article, the authors presented the first regional model of the magnetic field of Mercury developed with mathematical continuous functions, which has a horizontal spatial resolution of about 830 km at the surface of the planet, and it is derived without any a priori information about the geometry of the internal and external fields.

20 citations

Journal ArticleDOI
TL;DR: In this article, a magneto-hydrostatic model with spectropolarimetric properties close to those of solar photospheric magnetic bright points is constructed, and the horizontal component of the magnetic field is reconstructed using the self-similarity condition, while the magneto hydrostatic equilibrium condition is applied to the standard photosphere model with the magnetic fields embedded.
Abstract: Aims. A magneto-hydrostatic model is constructed with spectropolarimetric properties close to those of solar photospheric magnetic bright points. Methods. Results of solar radiative magneto-convection simulations are used to produce the spatial structure of the vertical component of the magnetic field. The horizontal component of magnetic field is reconstructed using the self-similarity condition, while the magneto-hydrostatic equilibrium condition is applied to the standard photospheric model with the magnetic field embedded. Partial ionisation processes are found to be necessary for reconstructing the correct temperature structure of the model. Results. The structures obtained are in good agreement with observational data. By combining the realistic structure of the magnetic field with the temperature structure of the quiet solar photosphere, the continuum formation level above the equipartition layer can be found. Preliminary results are shown of wave propagation through this magnetic structure. The observational consequences of the oscillations are examined in continuum intensity and in the Fe I 6302 A magnetically sensitive line.

20 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered the Weber-Davis model of the solar wind with alpha particles and showed that magnetic stresses pre-dominate the angular momentum loss of the Sun.
Abstract: The classic Weber-Davis model of the solar wind is reconsidered by incorporating alpha particles and by allowing the solar wind to flow out of the equatorial plane in an axisymmetrical configuration. In the ion momentum equations of the solar wind, the ion gyro-frequency is many orders of magnitude higher than any other frequency. This requires that the difference between proton and alpha velocity vectors be aligned with the background magnetic field. With the aid of this alignment condition, the governing equations of the multi-fluid solar wind are derived from the standard transport equations. The governing equations are numerically solved along a prescribed meridional magnetic field line located at colatitude $70^\circ$ at 1AU and a steady state fast solar wind solution is found. A general analysis concludes, in agreement with the Weber-Davis model, that the magnetic field helps the coronal plasma to achieve an effective corotation out to the Alfv\'enic radius, where the poloidal Alfv\'enic Mach number $M_T$ equals unity ($M_T$ is defined by equation (\ref{eq:mach})). The model computations show that, magnetic stresses predominate the angular momentum loss of the Sun. For the fast wind considered, the proton contribution to the angular momentum loss, which can be larger than the magnetic one, is almost completely canceled by the alpha particles that develop an azimuthal speed in the direction opposite to the solar rotation. The Poynting flux associated with the azimuthal components is negligible in the energy budget. However, the solar rotation can play some role in reducing the relative speed between alpha particles and protons for low latitude fast solar wind streams in interplanetary space.

20 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202312
202220
20181
201751
201656
201546