scispace - formally typeset
Search or ask a question
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.


Papers
More filters
Journal ArticleDOI
TL;DR: In this article, a minimization procedure was proposed to obtain a more chromosphere-like field using the measured photospheric field vectors as input, using force-free consistency integrals, spatial smoothing, and an improved match to the field direction as inferred from fibrils as can be observed in chromospheric Hα images.
Abstract: The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Nonlinear force-free codes have been shown to be useful in extrapolating the coronal field upward from underlying vector boundary data. However, we can only measure the magnetic field vector routinely with high accuracy in the photosphere, and unfortunately these data do not fulfill the force-free condition. We must therefore apply some transformations to these data before nonlinear force-free extrapolation codes can be self-consistently applied. To this end, we have developed a minimization procedure that yields a more chromosphere-like field, using the measured photospheric field vectors as input. The procedure includes force-free consistency integrals, spatial smoothing, and – newly included in the version presented here – an improved match to the field direction as inferred from fibrils as can be observed in, for example, chromospheric Hα images. We test the procedure using a model active-region field that included buoyancy forces at the photospheric level. The proposed preprocessing method allows us to approximate the chromospheric vector field to within a few degrees and the free energy in the coronal field to within one percent.

71 citations

Journal ArticleDOI
TL;DR: In this article, a transport model based on numerical solutions of a three-dimensional particle propagation model which includes pitch angle scattering and focused transport is applied to the intensity and anisotropy profiles measured on all three spacecraft.
Abstract: We analyze 65–105 keV electrons in the 7 February 2010 solar electron event observed simultaneously by STEREO-A, STEREO-B, and ACE. A method to reconstruct the full-electron pitch angle distributions from the four Solar Electron and Proton Telescope sensors on STEREO-A/B and the Solar Electron and Proton Telescope instrument on ACE in the energy range of approximately 60–300 keV for periods of incomplete angular coverage is presented. A transport modeling based on numerical solutions of a three-dimensional particle propagation model which includes pitch angle scattering and focused transport is applied to the intensity and anisotropy profiles measured on all three spacecraft. Based on an analysis of intensity gradients observed between the three spacecraft, we find that the lateral transport of the electrons occurs partially close to the Sun, due to effects of nonradial divergence of magnetic field lines or particle diffusion, and partially in the interplanetary medium. For the mean free paths characterizing the electron diffusion parallel and perpendicular to the interplanetary magnetic field, we derive values of λ∥∼ 0.1 AU and λ⟂∼ 0.01 AU. In comparison with results from other particle events which we had previously analyzed in a similar manner we discuss whether the diffusion mean free paths parallel and perpendicular to the average magnetic field might be related with each other, and whether the particle transport perpendicular to the average magnetic field is more likely due to particles following meandering magnetic field lines, or due to particles being scattered off individual field lines.

71 citations

Journal ArticleDOI
TL;DR: In this article, the authors defined the ϕ boundary as a more meaningful concept of the high-latitude limit to durably trapped ≥40-kev electrons than the usual intensity cutoff, and the average positions of each of these six "boundaries" are investigated as a function of invariant latitude, magnetic local time, and magnetic activity.
Abstract: The ϕ boundary was introduced in 1968 as a more meaningful concept of the high-latitude limit to durably trapped ≥40-kev electrons than the usual intensity cutoff. In the present study, this boundary is defined more precisely by using four different features of the latitude profile of the ϕ parameter. Two additional high-latitude boundaries, the intensity cutoff (Λc) and the background boundary (Λbkg) for ≥40-kev-electrons are defined, and the average positions of each of these six ‘boundaries’ are investigated as a function of invariant latitude, magnetic local time, and magnetic activity. A frequency of occurrence of isotropic and near-isotropic pitch-angle distributions for ≥40-kev electrons is also investigated as a function of magnetic local time and magnetic activity. The results of this study suggest that at least two separate mechanisms control the position of the high-latitude boundary as a function of magnetic local time. One mechanism operates continuously near midnight, but its effectiveness decreases monotonically with increasing local time through dawn and noon, then reaches a minimum in effectiveness in the late afternoon and dusk hours. A second mechanism operates only near the noon meridian (0800 to 1400 hours) and is the dominant mechanism in this local-time interval. There is also an indication that the orientation and symmetry axis of the boundary may change with time.

71 citations

Journal ArticleDOI
TL;DR: In this paper, the classically reducible problem in magnetogasdynamic steady inviscid flow is applied to the interaction of the solar plasma with planetary magnetic fields, and the results are consistent with Axford's order of magnitude calculation.

70 citations

Journal ArticleDOI
TL;DR: The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences.
Abstract: The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180° ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields. Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity, magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.

70 citations


Network Information
Related Topics (5)
Solar wind
26.1K papers, 780.2K citations
93% related
Atmosphere
30.8K papers, 737.8K citations
84% related
Magnetic field
167.5K papers, 2.3M citations
81% related
Radiative transfer
43.2K papers, 1.1M citations
79% related
Climate model
22.2K papers, 1.1M citations
78% related
Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202312
202220
20181
201751
201656
201546