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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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Journal ArticleDOI
TL;DR: In this paper, a principal component analysis of the axisymmetric magnetic field at the photosphere is carried out to find an optimal representation of the observed solar cycle, where the mean field is most efficient at representing the periodic field, but the median field is more efficient in representing the evolution of the diffuse field patterns.
Abstract: A principal component analysis, or proper orthogonal decomposition, of the axisymmetric magnetic field at the photosphere is carried out to find an optimal representation of the observed solar cycle. The 22-year periodic field requires just two modes. NSO Kitt Peak synoptic maps for Carrington rotations 1664–2007 were reduced by taking both the mean and the median field over longitude to produce two sequences of functions of sine latitude spanning 25.7 years. The lowest modes of each are determined by the polar fields. The mean field is most efficient at representing the periodic field, but the median field is more efficient at representing the evolution of the diffuse field patterns.

22 citations

Journal ArticleDOI
TL;DR: In this article, the authors used synoptic maps of a photospheric-vector magnetic field synthesized from the vector spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) to estimate free magnetic energy in the global scale.
Abstract: Context. The magnetic field permeating the solar atmosphere is generally thought to provide the energy for much of the activity seen in the solar corona, such as flares, coronal mass ejections (CMEs), etc. To overcome the unavailability of coronal magnetic field measurements, photospheric magnetic field vector data can be used to reconstruct the coronal field. Currently, there are several modelling techniques being used to calculate three-dimensional field lines into the solar atmosphere. Aims. For the first time, synoptic maps of a photospheric-vector magnetic field synthesized from the vector spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) are used to model the coronal magnetic field and estimate free magnetic energy in the global scale. The free energy (i.e., the energy in excess of the potential field energy) is one of the main indicators used in space weather forecasts to predict the eruptivity of active regions. Methods. We solve the nonlinear force-free field equations using an optimization principle in spherical geometry. The resulting threedimensional magnetic fields are used to estimate the magnetic free energy content E(sub free) = E(sub nlfff) − E(sub pot), which is the difference of the magnetic energies between the nonpotential field and the potential field in the global solar corona. For comparison, we overlay the extrapolated magnetic field lines with the extreme ultraviolet (EUV) observations by the atmospheric imaging assembly (AIA) on board the Solar Dynamics Observatory (SDO). Results. For a single Carrington rotation 2121, we find that the global nonlinear force-free field (NLFFF) magnetic energy density is 10.3% higher than the potential one. Most of this free energy is located in active regions.

22 citations

Journal ArticleDOI
TL;DR: In this paper, it has been suggested that the large scale structure of the interplanetary magnetic field can be deduced solely from solar wind speed measurements and indirect diagnostics such as measurements of the solar wind kinetic temperature and galactic and solar energetic particle modulations and anisotropics.
Abstract: It has recently been suggested that the large scale structure of the interplanetary magnetic field can be deduced solely from solar wind speed measurements. Here it is emphasized that, in addition to speed measurements, direct measurements of the interplanetary field and indirect diagnostics such as measurements of the solar wind kinetic temperature and galactic and solar energetic particle modulations and anisotropics are required to distinguish between open and closed magnetic structures in the solar wind.

22 citations

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional propagation of Alfvenic perturbations within the solar equatorial plane (SEP) in the solar wind with a spiral magnetic field was studied.
Abstract: We study a two-dimensional propagation of Alfvenic perturbations within the solar equatorial plane (SEP) in the solar wind with a spiral magnetic field. Analytical solutions within the entire frequency range are derived at large radial distance r. Numerical solutions which smoothly pass through the Alfven critical point rA are also obtained. Since the spiral magnetic field caused by the solar rotation scales as ∼r−1 at large r, the velocity and magnetic field perturbations, which are perpendicular to the SEP, remain small relative to the wind parameters in the entire radial range. The frequency criterion for the non-WKB radial scalings of the perturbation variables to appear is (f + mf⊙)² < fc², where f is the perturbation frequency, f⊙ is the solar rotation frequency, m is the azimuthal wavenumber, and fc is the well-known characteristic frequency determined by the wind parameters. We demonstrate that the process of continuous reflection in a spiral magnetic field and the effect of superposing Alfvenic perturbations with various f and m can lead to variations of the relative magnetic field fluctuation, the normalized cross helicity σc, the Alfven ratio ra, the magnetic perturbation energy density Eb, and the kinetic perturbation energy density Eυ, which differ from the predictions of the conventional WKB theory. In particular, the non-WKB radial scalings of the perturbation variables can appear at any timescales with appropriate values of m. The relevance of these results to data analyses on interplanetary fluctuations is discussed, and we emphasize the importance of obtaining fluctuation spectrum with respect to both f and m in the outer heliosphere.

22 citations

Journal ArticleDOI
TL;DR: Sondrestrom radar observations reveal that the dawn-dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection.
Abstract: Sondrestrom radar observations reveal that the dawn-dusk (By) component of the interplanetary magnetic field (IMF) strongly influences the nightside polar convection. This effect is quite complex. The convection for one orientation of By is not the mirror image of the other orientation. A positive By (i.e., pointing toward dusk) seems to organize the velocities such that, at all local times, they are predominantly westward within the radar field-of-view (approximately 68 deg-to-82 deg invariant latitude). Between dusk and midnight, on one such occasion, sunward flow is observed within the polar cap. In the midnight and dawn sectors, when By is negative, the plasma velocities often appear shifted toward early hours such that large southward velocities are observed about 3 hours before midnight. These are the only times when the predominant velocity component is southward.

22 citations


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