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A"}]}]}, "item_2_description_5": {"attribute_name": "\u6284\u9332", "attribute_value_mlt": [{"subitem_description": "For a realistic, highly stretched, two-dimensional tail configuration, in which the pressure gradient force is balanced with the curved field line tension force at the equator, the growth rates and the real frequencies of the ideal magnetohydrodynamic (MHD) and two component fluid (nonideal MHD) ballooning modes, in which the phrase \u201ctwo component fluid\u201d means that the Hall and the electron pressure gradient terms are included in the generalized Ohm\u0027s law, the ion bounce frequency \u03c9 bi , the ion magnetic drift frequency \u03c9 di , the ion diamagnetic drift frequency \u03c9*i , and the ion cyclotron frequency \u03c9 ci are calculated numerically at the equator as a function of X from the near-Earth tail (X = \u221215 R E ) to the midtail (X = \u221230 R E ). Contrary to the well-known dipole field case, in which the bounce frequency decreases with increasing \u2223X\u2223, the ion bounce frequency increases with \u2223X\u2223 for the tail configuration. The ion magnetic drift frequency dominated by the curvature drift frequency also increases with increasing \u2223X\u2223. The exact growth rates of the ideal and nonideal ballooning modes, \u03b3 e and \u03b3 ne , which are nearly equal, are given by 1.22V A /R c , where V A is the Alfv\u00e9n velocity and R c is the field line curvature radius at the equator, and satisfy \u03c9 bi , \u03c9 di , \u03c9*i \u003c \u03b3 e \u003c \u03c9 ci on average in the near-Earth tail at X \u223c \u221215 R E . Also, the ion motion remains adiabatic in the near-Earth tail at X \u223c \u221215 R E . Therefore it is a posteriori verified that the fluid or MHD description of the linear stability of the ballooning instability is valid, and the critical \u03b2 and the Alfv\u00e9n time scale \u03c4 A \u223c R c /V A of the ballooning instability onset obtained by the fluid theory are validated in the near-Earth tail as close as 15 R E from the Earth. Despite the plasma being collisionless and high-\u03b2 in the near-Earth tail, the subtle collisionless kinetic effects due to the field line curvature in high-\u03b2 collisionless plasma are not significant enough to invalidate the fluid description in the near-Earth tail. The Alfv\u00e9n time scale of an e-folding growth of the Alfv\u00e9n wave trapped within R c in the equatorial region is of the order of a few tens of seconds or less in the near-Earth tail. It is faster than the bounce time of the bulk of ions and can explain the observed rapid time scale of a substorm onset. 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Validity of the fluid description of critical β and Alfvén time scale of ballooning instability onset in the near-Earth collisionless high-β plasma
http://hdl.handle.net/2261/38136
256dc354-607f-4b0c-bd89-074109dd5eb9
| 名前 / ファイル | ライセンス | アクション | |
|---|---|---|---|
JGR_A109_NA02_02211.pdf (724.9 kB)
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| Item type | 学術雑誌論文 / Journal Article(1) | |||||
|---|---|---|---|---|---|---|
| 公開日 | 2016-12-28 | |||||
| タイトル | ||||||
| タイトル | Validity of the fluid description of critical β and Alfvén time scale of ballooning instability onset in the near-Earth collisionless high-β plasma | |||||
| 言語 | ||||||
| 言語 | eng | |||||
| キーワード | ||||||
| 主題 | ballooning instability | |||||
| 主題Scheme | Other | |||||
| キーワード | ||||||
| 主題 | MHD description | |||||
| 主題Scheme | Other | |||||
| キーワード | ||||||
| 主題 | collisionless high-beta plasma | |||||
| 主題Scheme | Other | |||||
| キーワード | ||||||
| 主題 | Alfvén time scale | |||||
| 主題Scheme | Other | |||||
| キーワード | ||||||
| 主題 | near-Earth tail | |||||
| 主題Scheme | Other | |||||
| キーワード | ||||||
| 主題 | substorm onset | |||||
| 主題Scheme | Other | |||||
| 資源タイプ | ||||||
| 資源 | http://purl.org/coar/resource_type/c_6501 | |||||
| タイプ | journal article | |||||
| 著者 |
Miura, Akira
× Miura, Akira |
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| 著者所属 | ||||||
| Department of Earth and Planetary Physics, University of Tokyo | ||||||
| 抄録 | ||||||
| 内容記述タイプ | Abstract | |||||
| 内容記述 | For a realistic, highly stretched, two-dimensional tail configuration, in which the pressure gradient force is balanced with the curved field line tension force at the equator, the growth rates and the real frequencies of the ideal magnetohydrodynamic (MHD) and two component fluid (nonideal MHD) ballooning modes, in which the phrase “two component fluid” means that the Hall and the electron pressure gradient terms are included in the generalized Ohm's law, the ion bounce frequency ω bi , the ion magnetic drift frequency ω di , the ion diamagnetic drift frequency ω*i , and the ion cyclotron frequency ω ci are calculated numerically at the equator as a function of X from the near-Earth tail (X = −15 R E ) to the midtail (X = −30 R E ). Contrary to the well-known dipole field case, in which the bounce frequency decreases with increasing ∣X∣, the ion bounce frequency increases with ∣X∣ for the tail configuration. The ion magnetic drift frequency dominated by the curvature drift frequency also increases with increasing ∣X∣. The exact growth rates of the ideal and nonideal ballooning modes, γ e and γ ne , which are nearly equal, are given by 1.22V A /R c , where V A is the Alfvén velocity and R c is the field line curvature radius at the equator, and satisfy ω bi , ω di , ω*i < γ e < ω ci on average in the near-Earth tail at X ∼ −15 R E . Also, the ion motion remains adiabatic in the near-Earth tail at X ∼ −15 R E . Therefore it is a posteriori verified that the fluid or MHD description of the linear stability of the ballooning instability is valid, and the critical β and the Alfvén time scale τ A ∼ R c /V A of the ballooning instability onset obtained by the fluid theory are validated in the near-Earth tail as close as 15 R E from the Earth. Despite the plasma being collisionless and high-β in the near-Earth tail, the subtle collisionless kinetic effects due to the field line curvature in high-β collisionless plasma are not significant enough to invalidate the fluid description in the near-Earth tail. The Alfvén time scale of an e-folding growth of the Alfvén wave trapped within R c in the equatorial region is of the order of a few tens of seconds or less in the near-Earth tail. It is faster than the bounce time of the bulk of ions and can explain the observed rapid time scale of a substorm onset. There is excellent agreement between the critical β and the Alfvén time scale obtained analytically for the two component fluid plasma and those obtained by a three-dimensional particle simulation. | |||||
| 書誌情報 |
Journal of geophysical research. A 巻 109, 号 2, p. A02211, 発行日 2004-02 |
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| ISSN | ||||||
| 収録物識別子タイプ | ISSN | |||||
| 収録物識別子 | 01480227 | |||||
| 書誌レコードID | ||||||
| 収録物識別子タイプ | NCID | |||||
| 収録物識別子 | AA10819721 | |||||
| DOI | ||||||
| 関連識別子 | ||||||
| 識別子タイプ | DOI | |||||
| 関連識別子 | info:doi/10.1029/2003JA009924 | |||||
| 権利 | ||||||
| 権利情報 | copyright 2004 by the American Geophysical Union | |||||
| 日本十進分類法 | ||||||
| 主題 | 450 | |||||
| 主題Scheme | NDC | |||||
| 出版者 | ||||||
| 出版者 | American Geophysical Union | |||||
