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Journal ArticleDOI

Discontinuities in an anisotropic plasma and their identification in the solar wind

01 Nov 1970-Planetary and Space Science (Pergamon)-Vol. 18, Iss: 11, pp 1611-1622
TL;DR: The types of discontinuity which can occur in a magnetohydrodynamic fluid with anistotropic pressure are discussed in this article, and rules are given for the identification of the type of discontinuities together with equations to determine their orientation and velocity.
About: This article is published in Planetary and Space Science.The article was published on 1970-11-01. It has received 343 citations till now. The article focuses on the topics: Shocks and discontinuities & Discontinuity (geotechnical engineering).
Citations
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Journal ArticleDOI
TL;DR: In this article, 11 passes of the ISEE satellites through the frontside terrestrial magnetopause were identified, where the plasma velocity in the magnetic field and boundary layer was substantially larger than in the magnetosheath, with a view to determining whether the velocity enhancements can be explained by magnetic field reconnection.
Abstract: Eleven passes of the ISEE satellites through the frontside terrestrial magnetopause were identified, where the plasma velocity in the magnetopause and boundary layer was substantially larger than in the magnetosheath. The nature of the plasma flow, magnetic field, and energetic particle fluxes in these regions were examined, with a view to determining whether the velocity enhancements can be explained by magnetic field reconnection.

756 citations

Journal ArticleDOI
15 Nov 1979-Nature
TL;DR: In this paper, high-speed plasma at the magnetopause in agreement with theoretical predictions of magnetic field reconnection is reported, and the observations agree with the predictions of the reconnection model of the dayside magnetopsause, in which the magnetic field is described as a rotational discontinuity, or a large-amplitude Alfven wave.
Abstract: Observations of high-speed plasma at the magnetopause in agreement with theoretical predictions of magnetic field reconnection are reported. Plasma ion and electron distributions measured by the quadrispherical analyzers on board the ISEE 1 and 2 spacecraft were obtained during the outbound traversal of the subsolar magnetopause. Plasma flow speeds of up to 450 km/sec were observed in the magnetopause layer, in contrast to speeds of 50 to 100 km/sec in the adjacent magnetosheath. The observations agree with the predictions of the reconnection model of the dayside magnetopause, in which the magnetopause is described as a rotational discontinuity, or a large-amplitude Alfven wave. It is noted that the lack of observations of plasma acceleration in most other cases of favorable magnetic field orientation could be a product of the rarity of magnetic recombination, or its small scale and nonstationarity.

625 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used the improved accuracy and time resolution of the IRM plasma measurements to reexamine the occurrence of high-speed flows as signatures of the reconnection process at the magnetopause.
Abstract: A total of 21 passes of AMPTE/IRM through the dayside (0800–1600 hours local time) low-latitude magnetospheric boundary region have been examined, all of which were characterized by large magnetic shear across the magnetopause. The purpose of the study was to use the improved accuracy and time resolution of the IRM plasma measurements to reexamine the occurrence of high-speed flows as signatures of the reconnection process at the magnetopause. A total of 12 of the 21 passes showed magnetopause crossings with high-speed flows. The duration of these flows was sometimes as short as 10 s and rarely more than 30 s. The occurrence of high-speed flows is inversely correlated with β, the ratio of plasma to magnetic pressure. For β 2 the average ratio is low (ΔV* = 0.18). We tentatively interpret this to indicate that reconnection may occur preferentially for low β values. A total of nine high-speed flows were subjected to quantitative momentum and energy balance test. The agreement between observations and theoretical predictions was generally quite good. The signs of the normal magnetic field, Bn, deduced from the momentum balance agreed with the sense of magnetic connection inferred independently from the measured proton heat flux direction. In one case the observations suggest that the satellite may have traversed the diffusion region of the reconnection process. The momentum balance results indicate that at times the effective mass of the ions in the magnetopause and boundary layer was of the order of twice the proton mass.

432 citations

Journal ArticleDOI
12 Jan 2006-Nature
TL;DR: Three-spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow imply that reconnection is fundamentally a large-scale process and reveal, surprisingly, that reconnections can operate in a quasi-steady-state manner even when undriven by the external flow.
Abstract: Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Frequent reports of small-scale flux ropes and flow channels associated with reconnection in the Earth's magnetosphere raise the possibility that reconnection is intrinsically patchy, with each reconnection X-line (the line along which oppositely directed magnetic field lines reconnect) extending at most a few Earth radii (R(E)), even though the associated current sheets span many tens or hundreds of R(E). Here we report three-spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow, where the reconnection X-line extended at least 390R(E) (or 2.5 x 10(6) km). Observations of this and 27 similar events imply that reconnection is fundamentally a large-scale process. Patchy reconnection observed in the Earth's magnetosphere is therefore likely to be a geophysical effect associated with fluctuating boundary conditions, rather than a fundamental property of reconnection. Our observations also reveal, surprisingly, that reconnection can operate in a quasi-steady-state manner even when undriven by the external flow.

274 citations

Journal ArticleDOI
TL;DR: In this article, the authors used magnetohydrodynamic (MHD) simulations to probe the nature of turbulence heating and found that significant inhomogeneous heating occurs in the solar wind, connected with current sheets that are dynamically generated by MHD turbulence.
Abstract: Solar wind observations and magnetohydrodynamic (MHD) simulations are used to probe the nature of turbulence heating. In particular, the electron heat flux, electron temperature, and ion temperature in the solar wind are studied using ACE and Wind data. These heating diagnostics are also compared with MHD simulation estimates of the local dissipation density. Coherent structures, which are sources of inhomogeneity and intermittency in MHD turbulence, are found to be associated with enhancements in every heating-related diagnostic. This supports the hypothesis that significant inhomogeneous heating occurs in the solar wind, connected with current sheets that are dynamically generated by MHD turbulence. Indeed, a subset of these coherent current sheets might be candidates for magnetic reconnection. However, the specific kinetic mechanisms that heat and accelerate particles within these structures require further study.

226 citations

References
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Book
01 Jan 1960
TL;DR: In this article, the propagation of electromagnetic waves and X-ray diffraction of X rays in crystals are discussed. But they do not consider the effects of superconductivity on superconducting conductors.
Abstract: Electrostatics of conductors Static magnetic field Superconductivity The propagation of electromagnetic waves Spatial dispersion Diffraction of X rays in crystals.

12,543 citations

Book
01 Jan 1964

305 citations

Journal ArticleDOI
TL;DR: In this paper, the existence of a field of MHD discontinuities in the solar wind should make possible the generation of ensembles of shocks and contact surfaces, which can be treated as shock wave or contact surface.
Abstract: The nonuniform emission of the solar wind from the sun means that conditions are established which favor the development of discontinuities in the plasma parameters. Since the solar wind is in rapid proper motion with respect to the sun and the earth, examination of these discontinuities requires that the wind velocity be transformed away. Then it is found that they satisfy the conditions of magnetohydrodynamics and can be treated as shock waves and the stationary contact surfaces consisting of either tangential or contact discontinuities. The collision-free structure of the solar wind suggests that the tangential discontinuity is the more likely contact surface as it is more capable of inhibiting diffusion which is required for a lifetime sufficient for the structure to be carried to the neighborhood of the earth. Either the shock wave or the contact surface can create signals that are detectable at the surface of the earth. The simplest surface signal to detect is the sudden impulse (SI) but other signals may be found. The existence of a field of MHD discontinuities in the solar wind should make possible the generation of ensembles of shocks and contact surfaces. Various possibilities are explored and these are discussed from the standpoint of combinations of sudden impulses at the earth's surface which are both positive and negative. Some of these are recurrent with a 27-day period; the interplanetary M region shock ensemble associated with this is discussed and the development of these structures in space is reviewed. Lastly observational evidence for interplanetary shock waves is given together with the analytic technique for establishing their geometry and comparing the derived and measured jump parameters. The applicability of the geometrical construction of the general class of MHD discontinuity to their analysis is indicated and shows the way in which the structural content of the solar wind can be classified by the use of magnetometers and plasma probes. A parametric study of the jump conditions through a shock wave can be used to verify the correctness of field measurements because of the redundancy in measurements. This also allows the details of shock structure to be examined including the intrinsic partitioning of the internal energy of the shocked plasma.

282 citations

Journal ArticleDOI
TL;DR: Power spectra and fluctuations of interplanetary magnetic field from Mariner 4 data for solar active and quiet days as mentioned in this paper, for both active and non-active solar active days.
Abstract: Power spectra and fluctuations of interplanetary magnetic field from Mariner 4 data for solar active and quiet days

275 citations

Journal ArticleDOI
TL;DR: In this paper, the authors describe and analyze the following micro-scale structures which were found in combined interplanetary magnetic field and plasma data obtained by the deep-space probe Pioneer-6: (1) Several types of simultaneous discontinuities in the magnetic fields and plasma parameters; (2) at least one clear example of a transitional region (D-sheet) associated with a plasma discontinuity; (3) other D-sheets which give evidence of magnetic field annihilation; inhomogeneous isothermal regions in which the square of the magnetic-field intensity is proportional to the
Abstract: This report describes and analyses the following micro-scale (≲.01 AU) structures which were found in combined interplanetary magnetic field and plasma data obtained by the deep-space probe, Pioneer-6: (1) Several types of simultaneous discontinuities in the magnetic field and plasma parameters; (2) at least one clear example of a transitional region (D-sheet) associated with a plasma discontinuity; (3) other D-sheets which give evidence of magnetic-field annihilation; (4) inhomogeneous isothermal regions in which the square of the magnetic-field intensity is proportional to the density; (5) periodic variations in the magnetic-field intensity which are associated with discontinuities in the bulk speed. It is suggested that small velocity discontinuities play a fundamental role in reducing stresses in the interplanetary medium, and that large-velocity discontinuities may give rise to waves and turbulence.

203 citations