2005 Fiscal Year Final Research Report Summary
Study of magnetohydrodynamic instabilities in high-β plasmas in the magnetosphere by theory and modelling
| Project/Area Number |
14540414
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Space and upper atmospheric physics
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| Research Institution | The University of Tokyo |
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Principal Investigator |
MIURA Akira The University of Tokyo, Graduate School of Science, Research Associate, 大学院・理学系研究科, 助手 (20126171)
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| Project Period (FY) |
2002 – 2005
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| Keywords | Magnetosphere / Magnetohydrodynamic Instability / High-beta plasma / 2-component fluid approximation / Kelvin-Helmholtz instability / Ballooning instabilty / Pressure gradient / Auroral electron acceleration |
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| Research Abstract |
In this research, linear characteristics of magnetohydrodynamic (MHD) instabilities in high-β plasmas in the magnetosphere have been studied within ideal MHD and two-component fluid approximations.
(1) It has been clarified by two-component fluid analysis that a Kelvin-Helmholtz (K-H) instability driven by a shear in the ion diamagnetic drift velocity and not in the electric field drift velocity is excited at the subsolar magnetopause. This instability is driven by the shear in the ion diamagnetic drift velocity, which is a nonideal MHD drift in a high-β plasma and is a macroscopic effect not visible at the guiding center level. The normalized growth rate decreases with an increase in the ratio of the magnetosheath density to the magnetospheric density.
(2) It has been clarified by two-component fluid analysis that ballooning instability in the high-β plasma in the geomagnetic tail has a westward propagating drift speed and also has a parallel electric field due to a perturbation in the electron pressure gradient, which is responsible for the auroral electron acceleration. For a highly stretched field line configuration in the geomagnetic tail, which is expected before the onset of substorms, the pitch angle average of ion bounce frequency was calculated. It was shown that at 15 Re from the Earth, the average ion bounce and magnetic drift frequencies are smaller than the ballooning growth rate obtained under the fluid approximations. Therefore, kinetic influences on ballooning instability are negligible within 15 Re from the Earth. However, beyond 15 Re the ion bounce and magnetic drift frequencies are larger than the ballooning growth rate and therefore, kinetic influences on ballooning instability are important beyond 15 Re from the Earth.
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