The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
M. Ugai - One of the best experts on this subject based on the ideXlab platform.
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Superfast expansion acceleration mechanism in the spontaneous fast magnetic reconnection
Advances in Space Research, 2002Co-Authors: T. Shimizu, M. UgaiAbstract:Abstract Thermodynamic supersonic (superfast) plasma expansion acceleration generated in the spontaneous fast magnetic reconnection process is studied in 2-dimensional magnetohydrodynamic (MHD) simulations. In contrast to the Petschek reconnection model, the reconnection outflow jet is found to exceed steadily the Alfven velocity measured in the upstream magnetic field region. In our MHD simulation for the symmetric anti-parallel magnetic field model, the final velocity of the plasma jet is observed to reach 1.4 times of the Alfven velocity, which is maintained until the jet encounters a fast shock generated in front of the magnetic loop (plasmoid). Also in asymmetric magnetic field models, in which the current sheet is put between two straight magnetic field regions with different intensities, the supersonic plasma acceleration mechanism is detected. Especially, in the asymmetric model in which uniform plasma density is initially assumed, the supersonic acceleration region tends to shift to the side of the higher intensity magnetic field region. In addition, the plasma jet region consists of two jet layers which have different Mach numbers and almost the same jet velocity. It means that the reconnection jet almost have reached a steady state. Hence, the generation of the superfast jet can be predicted by the Rankine Hugoniot Relation for the slow shock. Once the superfast jet and magnetic loop are generated, the thermodynamic supersonic expansion acceleration can occur due to the change of the pressure balance around the magnetic loop.
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Adiabatic expansion acceleration mechanism of superfast jets in the spontaneous fast magnetic reconnection model
Physics of Plasmas, 2000Co-Authors: T. Shimizu, M. UgaiAbstract:In contrast to the Petschek reconnection model, the plasma outflow jet in front of the plasmoid associated with the spontaneous fast reconnection model is found to exceed steadily the Alfven velocity measured in the upstream magnetic field region. According to two-dimensional magnetohydrodynamic simulations, the final velocity of the plasma jet is observed to be superfast and can reach 1.4 times of the Alfven velocity, which is maintained until the jet encounters a fast shock generated in front of the plasmoid. On the basis of the Rankine Hugoniot Relation and the Bernoulli equation, it is theoretically found that the superfast plasma jet generated by slow shocks associated with the reconnection process is effectively accelerated beyond the Alfven velocity by the adiabatic expansion of the plasma jet without any magnetic effect. In the plasma accelerations, the initial plasma acceleration caused in the slow shock is consistent with that of the Petschek reconnection model, but the subsequent plasma acceler...
Lou-chuang Lee - One of the best experts on this subject based on the ideXlab platform.
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Heliosphere Termination Shock as a Transformer of Magnetic Field from Lognormal to Normal Distribution
The Astrophysical Journal, 2008Co-Authors: M. Q. Chen, Jih-kwin Chao, Lou-chuang Lee, N. H. TingAbstract:A mechanism is proposed to demonstrate that the strength of magnetic field can be transformed from a lognormal to a normal distribution as the solar wind passes through the heliosphere termination shock (TS), which explains the recent Voyager 1 observations. The TS is approximated as a perpendicular MHD shock. Synthetic simulations using random picks of 3 × 107 upstream states generate the downstream magnetic field based on the Rankine-Hugoniot Relation across the TS. Thus, it is implicitly implied that the magnetic fluctuations are parallel to the shock surface. A lognormal distribution is transformed to a normal distribution for small plasma beta (β10 = 0.1), but for larger beta (β10 = 10), the distribution of B2 remains a lognormal. The observation of a normal magnetic field distribution downstream of the TS provides an upper bound (β10 < 1) for the solar wind beta near the TS, which in turn provides an upper bound for the number density of interstellar neutral hydrogens. One of the TS crossings from the Voyager 2 magnetic field and plasma observations on 2007 September 1 was found to have reformation of the local structure when the upstream beta, β10, without including pickup protons equals 0.04, which is a low-beta supercritical quasi-perpendicular shock.
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From Rankine‐Hugoniot Relation fitting procedure: Tangential discontinuity or intermediate/slow shock?
Journal of Geophysical Research: Space Physics, 2007Co-Authors: Hengqiang Feng, Caiyan Lin, Jih-kwin Chao, L. H. Lyu, Lou-chuang LeeAbstract:To identify an observed intermediate/slow shock, it is important to fit the measured magnetic fields and plasma on both sides using Rankine-Hugoniot (R-H) Relations. It is not reliable to determine an intermediate/slow shock only by the shock properties and fitting procedure based on one spacecraft observation, though previous reported intermediate/slow shocks are confirmed in such a way. We investigated two shock-like discontinuities, which satisfy the R-H Relations well. One meets the criterions of slow shocks and was reported as a slow shock, and another has all the characters of intermediate shock based on one spacecraft observation. However, both discontinuities also meet the requirements of tangential discontinuities and were confirmed as tangential discontinuities on large-scale perspective by using multi-spacecraft observations. We suggest that intermediate/slow shocks should be identified as carefully as possible and had better be determined by multi-spacecraft.
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from rankine hugoniot Relation fitting procedure tangential discontinuity or intermediate slow shock
Journal of Geophysical Research, 2007Co-Authors: H Q Feng, Caiyan Lin, Jih-kwin Chao, L. H. Lyu, Lou-chuang LeeAbstract:To identify an observed intermediate/slow shock, it is important to fit the measured magnetic fields and plasma on both sides using Rankine-Hugoniot (R-H) Relations. It is not reliable to determine an intermediate/slow shock only by the shock properties and fitting procedure based on one spacecraft observation, though previous reported intermediate/slow shocks are confirmed in such a way. We investigated two shock-like discontinuities, which satisfy the R-H Relations well. One meets the criterions of slow shocks and was reported as a slow shock, and another has all the characters of intermediate shock based on one spacecraft observation. However, both discontinuities also meet the requirements of tangential discontinuities and were confirmed as tangential discontinuities on large-scale perspective by using multi-spacecraft observations. We suggest that intermediate/slow shocks should be identified as carefully as possible and had better be determined by multi-spacecraft.
T. Shimizu - One of the best experts on this subject based on the ideXlab platform.
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Superfast expansion acceleration mechanism in the spontaneous fast magnetic reconnection
Advances in Space Research, 2002Co-Authors: T. Shimizu, M. UgaiAbstract:Abstract Thermodynamic supersonic (superfast) plasma expansion acceleration generated in the spontaneous fast magnetic reconnection process is studied in 2-dimensional magnetohydrodynamic (MHD) simulations. In contrast to the Petschek reconnection model, the reconnection outflow jet is found to exceed steadily the Alfven velocity measured in the upstream magnetic field region. In our MHD simulation for the symmetric anti-parallel magnetic field model, the final velocity of the plasma jet is observed to reach 1.4 times of the Alfven velocity, which is maintained until the jet encounters a fast shock generated in front of the magnetic loop (plasmoid). Also in asymmetric magnetic field models, in which the current sheet is put between two straight magnetic field regions with different intensities, the supersonic plasma acceleration mechanism is detected. Especially, in the asymmetric model in which uniform plasma density is initially assumed, the supersonic acceleration region tends to shift to the side of the higher intensity magnetic field region. In addition, the plasma jet region consists of two jet layers which have different Mach numbers and almost the same jet velocity. It means that the reconnection jet almost have reached a steady state. Hence, the generation of the superfast jet can be predicted by the Rankine Hugoniot Relation for the slow shock. Once the superfast jet and magnetic loop are generated, the thermodynamic supersonic expansion acceleration can occur due to the change of the pressure balance around the magnetic loop.
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Adiabatic expansion acceleration mechanism of superfast jets in the spontaneous fast magnetic reconnection model
Physics of Plasmas, 2000Co-Authors: T. Shimizu, M. UgaiAbstract:In contrast to the Petschek reconnection model, the plasma outflow jet in front of the plasmoid associated with the spontaneous fast reconnection model is found to exceed steadily the Alfven velocity measured in the upstream magnetic field region. According to two-dimensional magnetohydrodynamic simulations, the final velocity of the plasma jet is observed to be superfast and can reach 1.4 times of the Alfven velocity, which is maintained until the jet encounters a fast shock generated in front of the plasmoid. On the basis of the Rankine Hugoniot Relation and the Bernoulli equation, it is theoretically found that the superfast plasma jet generated by slow shocks associated with the reconnection process is effectively accelerated beyond the Alfven velocity by the adiabatic expansion of the plasma jet without any magnetic effect. In the plasma accelerations, the initial plasma acceleration caused in the slow shock is consistent with that of the Petschek reconnection model, but the subsequent plasma acceler...
Jih-kwin Chao - One of the best experts on this subject based on the ideXlab platform.
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Heliosphere Termination Shock as a Transformer of Magnetic Field from Lognormal to Normal Distribution
The Astrophysical Journal, 2008Co-Authors: M. Q. Chen, Jih-kwin Chao, Lou-chuang Lee, N. H. TingAbstract:A mechanism is proposed to demonstrate that the strength of magnetic field can be transformed from a lognormal to a normal distribution as the solar wind passes through the heliosphere termination shock (TS), which explains the recent Voyager 1 observations. The TS is approximated as a perpendicular MHD shock. Synthetic simulations using random picks of 3 × 107 upstream states generate the downstream magnetic field based on the Rankine-Hugoniot Relation across the TS. Thus, it is implicitly implied that the magnetic fluctuations are parallel to the shock surface. A lognormal distribution is transformed to a normal distribution for small plasma beta (β10 = 0.1), but for larger beta (β10 = 10), the distribution of B2 remains a lognormal. The observation of a normal magnetic field distribution downstream of the TS provides an upper bound (β10 < 1) for the solar wind beta near the TS, which in turn provides an upper bound for the number density of interstellar neutral hydrogens. One of the TS crossings from the Voyager 2 magnetic field and plasma observations on 2007 September 1 was found to have reformation of the local structure when the upstream beta, β10, without including pickup protons equals 0.04, which is a low-beta supercritical quasi-perpendicular shock.
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From Rankine‐Hugoniot Relation fitting procedure: Tangential discontinuity or intermediate/slow shock?
Journal of Geophysical Research: Space Physics, 2007Co-Authors: Hengqiang Feng, Caiyan Lin, Jih-kwin Chao, L. H. Lyu, Lou-chuang LeeAbstract:To identify an observed intermediate/slow shock, it is important to fit the measured magnetic fields and plasma on both sides using Rankine-Hugoniot (R-H) Relations. It is not reliable to determine an intermediate/slow shock only by the shock properties and fitting procedure based on one spacecraft observation, though previous reported intermediate/slow shocks are confirmed in such a way. We investigated two shock-like discontinuities, which satisfy the R-H Relations well. One meets the criterions of slow shocks and was reported as a slow shock, and another has all the characters of intermediate shock based on one spacecraft observation. However, both discontinuities also meet the requirements of tangential discontinuities and were confirmed as tangential discontinuities on large-scale perspective by using multi-spacecraft observations. We suggest that intermediate/slow shocks should be identified as carefully as possible and had better be determined by multi-spacecraft.
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from rankine hugoniot Relation fitting procedure tangential discontinuity or intermediate slow shock
Journal of Geophysical Research, 2007Co-Authors: H Q Feng, Caiyan Lin, Jih-kwin Chao, L. H. Lyu, Lou-chuang LeeAbstract:To identify an observed intermediate/slow shock, it is important to fit the measured magnetic fields and plasma on both sides using Rankine-Hugoniot (R-H) Relations. It is not reliable to determine an intermediate/slow shock only by the shock properties and fitting procedure based on one spacecraft observation, though previous reported intermediate/slow shocks are confirmed in such a way. We investigated two shock-like discontinuities, which satisfy the R-H Relations well. One meets the criterions of slow shocks and was reported as a slow shock, and another has all the characters of intermediate shock based on one spacecraft observation. However, both discontinuities also meet the requirements of tangential discontinuities and were confirmed as tangential discontinuities on large-scale perspective by using multi-spacecraft observations. We suggest that intermediate/slow shocks should be identified as carefully as possible and had better be determined by multi-spacecraft.
Dc Daan Schram - One of the best experts on this subject based on the ideXlab platform.
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Anomalous atomic hydrogen shock pattern in a supersonic plasma Jet
Physical review letters, 2000Co-Authors: Stéphane Mazouffre, Mgh Maarten Boogaarts, Van Der Jjam Joost Mullen, Dc Daan SchramAbstract:A two-photon laser-induced fluorescence study on the transport of ground-state atomic hydrogen in a supersonic plasma jet, generated from an Ar-H/sub 2/ mixture, reveals an unexpected shock pattern. Whereas both the axial-velocity profile and the temperature profile of hydrogen atoms along the jet centerline can be interpreted in terms of a supersonic expansion of an Ar-H gas mixture, the H-atom density profiles do not satisfy the well established Rankine-Hugoniot Relation leading to a nonconservation of the forward flux. The experimental results show that H atoms escape from the supersonic expansion by a diffusion process due to strong density gradients between the core of the jet and its vicinity
