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, satellite observations of spatially localized regions of electron and ion precipitation with concomitant paired upward and downward fieldaligned currents and duskward electric field enhancements at high (> 80° invariant latitude) magnetic latitudes are presented.
Abstract: FAST satellite observations of spatially localized regions of electron and ion precipitation with concomitant paired upward and downward field-aligned currents and duskward electric field enhancements at high (> 80° invariant latitude) magnetic latitudes are presented. Each pass of several across the polar cap was made during a period of persistent northward interplanetary magnetic field, and was characterized by the presence of several of these precipitation regions. In each case, the precipitation regions were associated with jets of enhanced antisunward convection, with electron precipitation restricted to the upward current region, and no energetic electron outflow in the downward current region, and ion precipitation spread over broader regions, possibly by time-of-flight effects. We compare these low-altitude features to those expected for source regions lying in a reconnection site at the lobe magnetopause, a bursty bulk flow in the plasma sheet, and a surface wave on the low-latitude boundary layer (LLBL). We find that the lobe reconnection model successfully describes the observed electrodynamics of the arcs, as well as the electron and ion source temperatures, but can not readily explain the presence of precipitating O+ and He+ in addition to H+ and He++. The plasma sheet source model can explain the composition of the ion precipitation but predicts higher electron and ion source temperatures than are observed, may require the coincidence of bursty bulk flows with extensions of the plasma sheet into the lobe, and may not be consistant with other observations of auroral phenomenology. The LLBL surface wave model does not readily explain the observed electrodynamics of the arcs and is not consistent with the observed offsets between electron and ion precipitation.
26 citations
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TL;DR: In this paper, a model of the atmosphere of chemically peculiar magnetic stars was developed, where the surface distribution of a magnetic field was assumed to be a dipole, slightly distorted by the induced atmospheric electric current, which may change the atmospheric structure and provide insight into the formation and evolution of stellar magnetic fields.
Abstract: We discuss the properties of atmospheres of chemically peculiar magnetic stars. The slow evolution of global mag- netic fields leads to the development of an induced electric current in all conductive atmospheric layers. The Lorentz force, which results from the interaction between a magnetic field and the induced current, may change the atmospheric structure and provide insight into the formation and evolution of stellar magnetic fields. We developed a model atmosphere code that takes into account the Lorentz force in the equation of hydrostatic equilibrium, and computed a number of model atmospheres for magnetic A and B stars. The surface distribution of a magnetic field was assumed to be a dipole, slightly distorted by the induced atmospheric electric current. The interaction between the magnetic field and electric current is modelled in detail, tak- ing into account microscopic properties of the stellar plasma. The presence of a significant Lorentz force leads to substantial modification of the atmospheric structure and in particular the pressure stratification, which in turn influences the formation of absorption spectral features, especially hydrogen Balmer lines. Furthermore, we find that rotational modulation of the disk- average parameters of a global stellar magnetic field causes characteristic rotational variability of hydrogen lines. With our model, observable effects correspond to induced electric currents of the order of 10 −11 cgs, which requires characteristic field evolution times 2-3 orders of magnitude shorter than the field decay time estimated for magnetic A and B stars assuming fossil dipolar field topology in the stellar interior. Using the computations of our model atmospheres we consider an observational aspect of the problem and attempt to interpret photometric data on the variability of hydrogen lines within the framework of simplest model of the evolution of global magnetic fields. With the hydrogen line data we find tentative support for the presence of a non-negligible Lorentz force in the atmospheres of some magnetic chemically peculiar stars.
26 citations
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TL;DR: In this article, a computer program for transforming spherical harmonic coefficients to geomagnetic dipole coordinates is presented, which can be used to transform spherical harmonic functions to geOMagnetic dipoles.
Abstract: Computer program for transforming spherical harmonic coefficients to geomagnetic dipole coordinates
26 citations
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TL;DR: In this article, the spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14), Halley (L =4), and Siple(L=4).
Abstract: The spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14), Halley (L=4), and Siple (L=4). Frequently, the waveforms of ELF-VLF signals simultaneously received at each site were identical. Although of similar frequency structure, the waveforms of the accompanying Pc3 magnetic pulsations did not show a one-to-one association. Whereas both are dayside phenomena, QP emissions occur over a smaller range of local times, and have a maximum of occurrence later in the day closer to local noon. QP emissions are identified with the periodic modulation of the electron pitch-angle distribution by the propagation of ULF compressional fast-mode waves through a region. However, contrary to previous ideas, rising-tone emissions do not represent the frequency-time signatures of such waves. In addition to generation close to the equatorial plane, we propose an additional high-latitude source of QP emissions. These emissions are associated with regions of minimum B produced by the dayside compression of the magnetosphere close to the magnetopause. Model magnetic field calculations of these minimum-B regions as a function of magnetic local time and invariant latitude are presented.
26 citations
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TL;DR: In this paper, the authors analyzed the time series of the interplanetary and Earth's magnetotail magnetic fields and found that the magnetic field increment distributions are non-Gaussian, but self-affine.
Abstract: The time series of the interplanetary and Earth’s magnetotail magnetic fields are analyzed. The data subsets taken by the IMP 8 spacecraft outside and inside of the Earth’s magnetosphere show clearly the fractal properties: their “box dimensions” are found to be close to 1.7 and 1.5 respectively. It is shown that data gaps have a little effect on the results. The magnetic field increment distributions are found to be non-Gaussian, but self-affine.
26 citations