The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform
L. A. Frank - One of the best experts on this subject based on the ideXlab platform.
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Pressure, volume, density relationships in the plasma sheet
Journal of Geophysical Research, 2004Co-Authors: Richard L. Kaufmann, William R. Paterson, L. A. FrankAbstract:The entropy parameter Pn � 5/3 was found to be relatively uniform throughout the region studied. The energy parameter TV 2/3 decreased by 40% for ions and 10% for electrons near midnight between � 29.5 and � 11.5 RE. These energy parameter changes suggest that the most energetic ions and electrons are either being deenergized or preferentially lost, processes that may be associated with gradient and curvature drifts through the sides of the convecting flux tubes or by wave instabilities and a parallel heat flux. INDEX TERMS: 2764 Magnetospheric Physics: Plasma sheet; 2744 Magnetospheric Physics: Magnetotail; 2760 Magnetospheric Physics: Plasma convection; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; KEYWORDS: plasma sheet, magnetotail, pressure balance inconsistency, 3-D models
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Birkeland currents in the plasma sheet
Journal of Geophysical Research, 2003Co-Authors: Richard L. Kaufmann, William R. Paterson, L. A. FrankAbstract:Received 30 August 2002; revised 1 April 2003; accepted 22 April 2003; published 23 July 2003. [1] Geotail particle and magnetic field measurements were combined to generate long-term-averaged 3-D models of the plasma sheet. Ampere’s law was used to calculate the Birkeland current jk in the � 30 1 RE region. Current diversion, or the growth of current in a unit flux tube jk/B, took place throughout the region studied. This suggests that electron scattering is broadly distributed. No substantial change in jk/B could be detected between the plasma sheet boundary layer and the ionosphere. Birkeland currents were strongest and exhibited a dawn-dusk asymmetry when the interplanetary magnetic field (IMF) was southward. This asymmetry may be associated with the formation of thin current sheets on the dusk side during disturbed periods. Symmetries were apparent above and below the neutral sheet when the IMF was northward or southward, but these symmetries were not present when the IMF pointed dawnward or duskward. For these latter cases, separate surfaces were found on which Bx =0 ,By = 0, and jk = 0. This apparently complex structure could be understood as a consequence of the tendency for By in the neutral sheet to have the same sign as the IMF By. The observed Birkeland currents were in the region 1 sense when leaving the plasma sheet for all IMF orientations. Current diversion was analyzed in an MHD framework. The analysis suggested that the reduction of gradient and curvature guiding center drifts, and the presence of polarization currents in the diversion region can provide sources of electrons to sustain a steady jk. It also was noted that the formation of an Ek region in the topside ionosphere can make it appear to the conducting ionosphere as if it is being driven by a current source rather than by the plasma sheet electric field. INDEX TERMS: 2764 Magnetospheric Physics: Plasma sheet; 2708 Magnetospheric Physics: Current systems (2409); 2744 Magnetospheric Physics: Magnetotail; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions;
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Report of the Magnetospheric Physics panel
1991Co-Authors: James L. Burch, L. A. Frank, Thomas A. Potemra, Maha Ashour-abdalla, Daniel N. Baker, Cynthia A Cattell, Andrew F. Chang, Christoph K. Goertz, Margaret G. Kivelson, Lou-chuang LeeAbstract:Magnetospheric research is a relatively new area in the study of the Earth's environment. The present report attempts to overview past and future research on this topic. The goals of Magnetospheric research are numerous, and include: understanding large scale magnetospheres of the Earth and other planets; understanding the plasma physical processes operating within the various magnetospheres; to understand how mass, energy and momentum are transmitted from the solar wind; to understand quantitatively the coupling between magnetospheres and their ionospheres; and to understand the Magnetospheric mechanisms which accelerate particles to high energies, as well as the ultimate fate of these particles. The report continues on to summarize a number of proposed space missions aimed at data acquisition. Finally, there is a brief discussion of the theory and modeling of magnetospheres.
S.-i. Akasofu - One of the best experts on this subject based on the ideXlab platform.
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LONG-STANDING UNSOLVED PROBLEMS IN SOLAR Physics AND Magnetospheric Physics
Multiscale Coupling of Sun-Earth Processes, 2005Co-Authors: S.-i. AkasofuAbstract:Abstract For many decades, there have existed a number of long-standing, unsolved problems in solar Physics and Magnetospheric Physics. It is suggested that some of them remain unsolved because the guiding concepts, or paradigms, have no sound foundation. Here several paradigms are chosen for examination, in light of the related observations. They are the ionization rate of the solar wind, sunspots, solar flares/CMES, magnetic clouds, the concept of magnetic flux transfer in the magnetosphere, the diversion of the cross-tail current, and the dipolarization and substorm onset. It is obviously not the intent of this paper to provide answers to those difficult problems. Rather, here are posed basic questions about the sources of the established paradigms, and a suggestion that the established paradigms are not necessarily the final answers.
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A new field‐aligned current index AF and its relation to the storm‐time ring current and energetic neutral atom (ENA) emissions
Geophysical Research Letters, 2002Co-Authors: Wei Sun, S.-i. AkasofuAbstract:[1] It is shown that a newly devised field-aligned current index AF is well correlated with the Dst index, the correlation coefficient being 0.93. The AF index is based on the fact that geomagnetic Y (or D) component variations in the middle and low latitudes are mainly caused by field-aligned currents. It is also demonstrated that energetic neutral atom (ENA) emissions measured by the Geotail satellite are well correlated with the AF index. INDEX TERMS: 2778 Magnetospheric Physics: Ring Current; 2716 Magnetospheric Physics: Energetic particles precipitating; 2708 Magnetospheric Physics: Current Systems (2409); 2788 Magnetospheric Physics: Storms and Substorms; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions
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New scheme provides a first step toward geomagnetic storm prediction
Eos Transactions American Geophysical Union, 1996Co-Authors: S.-i. AkasofuAbstract:Establishing a geomagnetic storm prediction scheme is like constructing a car, and the four disciplines of solar Physics, solar wind Physics, Magnetospheric Physics, and thermospheric (ionospheric) Physics are like the car's parts. Unfortunately, in spite of much progress in the separate disciplines in the past, there has been little effort to integrate them. As constructing a car is different from improving its parts, considerable effort is needed to integrate solar Physics, solar wind Physics, Magnetospheric Physics, and thermospheric Physics into a single discipline of geomagnetic storm prediction.
Jörg Büchner - One of the best experts on this subject based on the ideXlab platform.
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Theory and Simulation of Reconnection
Space Science Reviews, 2006Co-Authors: Jörg BüchnerAbstract:Reconnection is a major commonality of solar and Magnetospheric Physics. It was conjectured by Giovanelli in 1946 to explain particle acceleration in solar flares near magnetic neutral points. Since than it has been broadly applied in space Physics including Magnetospheric Physics. In a special way this is due to Harry Petschek, who in 1994 published his ground breaking solution for a 2D magnetized plasma flow in regions containing singularities of vanishing magnetic field. Petschek’s reconnection theory was questioned in endless disputes and arguments, but his work stimulated the further investigation of this phenomenon like no other. However, there are questions left open. We consider two of them — “anomalous” resistivity in collisionless space plasma and the nature of reconnection in three dimensions. The Cluster and SOHO missions address these two aspects of reconnection in a complementary way — the resistivity problem in situ in the magnetosphere and the 3D aspect by remote sensing of the Sun. We demonstrate that the search for answers to both questions leads beyond the applicability of analytical theories and that appropriate numerical approaches are necessary to investigate the essentially nonlinear and nonlocal processes involved. Necessary are both micro-physical, kinetic Vlasov-equation based methods of investigation as well as large scale (MHD) simulations to obtain the geometry and topology of the acting fields and flows.
A. T. Y. Lui - One of the best experts on this subject based on the ideXlab platform.
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electric current approach to Magnetospheric Physics and the distinction between current disruption and magnetic reconnection
Geophysical monograph, 2013Co-Authors: A. T. Y. LuiAbstract:The debate on whether the primary quantities in Magnetospheric Physics are the magnetic field combined with the plasma bulk flow or the electric field combined with the current density has been raging on and off for decades. The former approach is known as the Bu paradigm and the latter as the Ej paradigm. The first tutorial for the Conference on Magnetospheric Current Systems advocates that the correct approach to understanding Magnetospheric problems is in terms of the Bu paradigm. In this paper, we address the limitations of the Bu paradigm and consider the merits of the Ej paradigm, with some emphasis on the magnetotail current. The concept of magnetic reconnection is formulated in the Bu paradigm and that of current disruption is formulated in the Ej paradigm. Since the usefulness of these two concepts and their distinction from each other is central to this debate, we discuss also the similarities and differences between them. We conclude by pointing out that each paradigm has its merits and limitations, and which one is the better approach should depend on the Magnetospheric phenomenon to be investigated. Insisting on one paradigm being superior than the other for treating all Magnetospheric problems would stifle innovative thinking in scientific pursuits.
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Data‐derived forecasting model for relativistic electron intensity at geosynchronous orbit
Geophysical Research Letters, 2004Co-Authors: Aleksandr Y. Ukhorskiy, M. I. Sitnov, A. S. Sharma, Brian J. Anderson, Shinichi Ohtani, A. T. Y. LuiAbstract:[1] In this paper we present a data-derived model of relativistic electron flux at geosynchronous orbit. The model is driven by multiple solar wind and Magnetospheric inputs and combines the deterministic approach of nonlinear dynamics with conditional probability consideration. The model is used for one-day predictions of daily flux maxima for the years 1995–2000. The deterministic part of the model yields average prediction efficiency of 0.77 and linear correlation coefficient of 0.89. It identifies solar wind velocity and SymH index as most relevant input parameters. The probabilistic part of the model quantifies the risks of deviations from deterministic predictions as a function of average solar wind and magnetosphere conditions. INDEX TERMS: 2720 Magnetospheric Physics: Energetic particles, trapped; 2722 Magnetospheric Physics: Forecasting; 2730 Magnetospheric Physics: Magnetosphere— inner; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 3220 Mathematical GeoPhysics: Nonlinear dynamics. Citation: Ukhorskiy, A. Y., M. I. Sitnov, A. S. Sharma, B. J. Anderson, S. Ohtani, and A. T. Y. Lui (2004), Data-derived forecasting model for relativistic electron intensity at geosynchronous orbit, Geophys. Res. Lett., 31, L09806,
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Current controversies in Magnetospheric Physics
Reviews of Geophysics, 2001Co-Authors: A. T. Y. LuiAbstract:The scientific ascent of humankind comes in two forms: incremental progress with traditional thinking, and paradigm transition. The latter typically engenders intense debate, often long lasting, before the transition of the paradigm is deemed acceptable. The Magnetospheric discipline is no exception, especially in view of the sparse observations available to reach conclusive theory-data closure. Scientific controversies serve an important role in identifying significant unresolved issues for progress to be made. This review highlights key issues on four controversies present in Magnetospheric Physics: (1) the on-and-off debate on whether the magnetic field combined with the plasma bulk flow or the electric field combined with the current density is the primary quantity in treating Magnetospheric problems; (2) the proper interpretation of transient dayside Magnetospheric phenomena, i.e., whether they are related to flux transfer events, plasma transfer events, or solar wind pressure pulses; (3) the physical processes responsible for substorm onset; and (4) justifications for substorms or enhanced Magnetospheric convection as the cause of magnetic storms. In issue 1 the merits and limitations of the two approaches are expounded. In issue 2 the predicted similarities and differences between the three interpretations are summarized. In issue 3 the strengths and weaknesses of prominent existing substorm models are elaborated on. In issue 4 the two contributors to storms are recognized and combined. Each controversy has an element of a paradigm transition. The resolutions of these controversies appear to also have one common element in that the presumption of only one theory to be correct may not be valid; a synthesis of existing theories may provide a better understanding of all features associated with the phenomenon.
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Magnetospheric Current Systems - Electric Current Approach to Magnetospheric Physics and the Distinction Between Current Disruption and Magnetic Reconnection
Magnetospheric Current Systems, 2000Co-Authors: A. T. Y. LuiAbstract:The debate on whether the primary quantities in Magnetospheric Physics are the magnetic field combined with the plasma bulk flow or the electric field combined with the current density has been raging on and off for decades. The former approach is known as the Bu paradigm and the latter as the Ej paradigm. The first tutorial for the Conference on Magnetospheric Current Systems advocates that the correct approach to understanding Magnetospheric problems is in terms of the Bu paradigm. In this paper, we address the limitations of the Bu paradigm and consider the merits of the Ej paradigm, with some emphasis on the magnetotail current. The concept of magnetic reconnection is formulated in the Bu paradigm and that of current disruption is formulated in the Ej paradigm. Since the usefulness of these two concepts and their distinction from each other is central to this debate, we discuss also the similarities and differences between them. We conclude by pointing out that each paradigm has its merits and limitations, and which one is the better approach should depend on the Magnetospheric phenomenon to be investigated. Insisting on one paradigm being superior than the other for treating all Magnetospheric problems would stifle innovative thinking in scientific pursuits.
H. Rème - One of the best experts on this subject based on the ideXlab platform.
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Global control of merging by the interplanetary magnetic field: Cluster observations of dawnside flank magnetopause reconnection
Journal of Geophysical Research, 2004Co-Authors: Stefan Eriksson, Scot R. Elkington, T. D. Phan, S. M. Petrinec, H. Rème, Malcolm Dunlop, Michael Wiltberger, André Balogh, Robert Ergun, Mats AndréAbstract:rm 0 p with the expected direction of the normal magnetic field and so we interpret them as speed changes due to magnetic reconnection. The observed directions of DV compare very well with the location of the simulated MHD sash relative to Cluster. The magnetic field shear in the locally tangential plane of the magnetopause ranges between 171� and 177� for the 30 June event in good agreement with antiparallel merging at the MHD sash. The corresponding local field shear for the 29 May event is only 144� , either suggesting a component merging site in the direction of the sash or indicating that Cluster is farther away from the location where the neutral line was initially formed as compared with the 30 June event. A comparison between the projected regions of antiparallel and component merging onto the magnetopause and the quasi-steady directionofplasmaaccelerationdetectedbyClusteron29Mayand30Junesupporttheview that the IMF controls the expected global location of magnetic reconnection at limited regions of the magnetopause. This is in contrast to randomly distributed merging sites over the dayside magnetopause that in principle could generate accelerated flows away from the observed directions of DV. INDEX TERMS: 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 2740 Magnetospheric Physics: Magnetospheric configuration and dynamics; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 7835 Space Plasma Physics: Magnetic reconnection; KEYWORDS: flank magnetic reconnection, MHD sash
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Walen and slow-mode shock analyses in the near-Earth magnetotail in connection with a substorm onset on 27 August 2001
Journal of Geophysical Research, 2004Co-Authors: Stefan Eriksson, C. G. Mouikis, Daniel N. Baker, H. Rème, Malcolm Dunlop, Robert Ergun, Marit Øieroset, Andris Vaivads, André BaloghAbstract:plasma density N � 0.3 cm � 3 and the plasma ion b � 1.5. The Walen analysis applied to the tailward flow interval from 0400:36 UT to 0403:14 UT is consistent with the ions being accelerated to � 73% of the Alfven speed across a slow-mode shock connected to a near-Earth neutral line located on the earthward side of the spacecraft. The occurrence of a small plasmoid-type magnetic flux rope during the leading edge of the tailward flows provides further support in favor of an active region of magnetic reconnection earthward of Cluster. The more field-aligned earthward flows between 0406 UT and 0408 UT, however, failed to satisfy the Walen test. Rankine-Hugoniot analyses of upstream and downstream plasma and magnetic field parameters confirm the presence of a slow-mode shock in connection with the passage of the tailward flow region but not with the 0406 UT to 0408 UT earthward flow interval. The confirmed shock satisfies the critical slow-mode requirements: MI * � 1.0 and MSM * > 1.0 on the upstream side and MSM * � 19 RE of the near-Earth magnetotail. INDEX TERMS: 7835 Space Plasma Physics: Magnetic reconnection; 7851 Space Plasma Physics: Shock waves; 2744 Magnetospheric Physics: Magnetotail; 2788 Magnetospheric Physics: Storms and substorms; KEYWORDS: magnetic reconnection, shock waves, magnetotail boundary layers
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Correlation between suprathermal electron bursts, broadband extremely low frequency waves, and local ion heating in the midaltitude cleft/low‐latitude boundary layer observed by Cluster
Journal of Geophysical Research, 2004Co-Authors: Yulia Bogdanova, H. Rème, Mats André, Christopher J. Owen, Andrew Fazakerley, B. Klecker, Nicole Cornilleau-wehrlin, Benjamin Grison, Peter J. Cargill, J. M. BosquedAbstract:with localized extra low frequency (ELF) (1–10 Hz) magnetic field wave power with broadband spectra. Our study shows that strong ion heating was observed only in the region with electron field-aligned anisotropy more than 2. In addition, comparison of particle data from two spacecraft, which crossed the heating region with a time difference of 4 min, shows the correlation between ion outflow fluxes and fluxes of the injected electrons. Whereas ELF electromagnetic waves are localized inside the ion heating region, ELF electrostatic waves are detected throughout the cleft/cusp/mantle regions, where strong ion heating was not observed, suggesting that electromagnetic ELF waves heat ions in the cleft region. Owing to the absence of magnetosheath ions and strong field-aligned currents, we suppose that inside ‘‘electron-only’’ cleft region the suprathermal electron bursts are most likely an energy source for the wave destabilization. We suggest that the location of the heating region and the level of the outflow ion fluxes could be related to electron injection in the cleft in such events. INDEX TERMS: 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers; 2736 Magnetospheric Physics: Magnetosphere/ionosphere interactions; 7807 Space Plasma Physics: Charged particle motion and acceleration; 7867 Space Plasma Physics: Wave/particle interactions; KEYWORDS: cleft electron observations, dayside ion outflow, ion heating in the cleft/cusp, wave/ particle interaction
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Cluster observations of the high-latitude magnetopause and cusp: initial results from the CIS ion instruments
Annales Geophysicae, 2001Co-Authors: J. M. Bosqued, Iannis Dandouras, T. D. Phan, H. Rème, C. P. Escoubet, A. Balogh, M. W. Dunlop, D. Alcaydé, Ermanno Amata, M. B. Bavassano-cattaneoAbstract:Abstract. Launched on an elliptical high inclination orbit (apogee: 19.6 RE) since January 2001 the Cluster satellites have been conducting the first detailed three-dimensional studies of the high-latitude dayside magnetosphere, including the exterior cusp, neighbouring boundary layers and magnetopause regions. Cluster satellites carry the CIS ion spectrometers that provide high-precision, 3D distributions of low-energy ( Key words. Magnetospheric Physics (magnetopause, cusp, and boundary layers; magnetosheath) Space plasma Physics (magnetic reconnection)
