Study of magnetohydrodynamic instabilities in high-β plasmas in the magnetosphere by theory and modelling

通过理论和模型研究磁层高β等离子体中的磁流体动力学不稳定性

• 批准号: 14540414
• 负责人: MIURA Akira
• 金额: $ 1.41万
• 依托单位: The University of Tokyo
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2002
• 资助国家: 日本
• 起止时间: 2002 至 2005
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14540414/
• 关键词: Magnetosphere; Magnetohydrodynamic Instability; High-beta plasma; 2-component fluid approximation; Kelvin-Helmholtz instability; Ballooning instabilty; Pressure gradient; Auroral electron acceleration; エネルギー原理; 交換型不安定; 電離層; サブストームオンセット; 磁気圏尾部

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.

在本研究中，我们在理想 MHD 和二组分流体近似下研究了磁层中高 β 等离子体中磁流体动力学 (MHD) 不稳定性的线性特征。(1) 通过二组分流体分析阐明了开尔文-亥姆霍兹 (K-H) 不稳定性是由离子反磁性漂移速度中的剪切驱动的，而不是由电场漂移速度中的剪切驱动的，这在太阳下磁层顶处被激发。不稳定性是由离子抗磁漂移速度的剪切驱动的，这是高β等离子体中的非理想MHD漂移，并且是在引导中心水平上不可见的宏观效应。归一化增长率随着比率的增加而降低。 (2)通过二组分流体分析阐明了地磁尾部高β等离子体中的气球状不稳定性具有向西传播的漂移速度和由于电子压力梯度的扰动，也有一个平行电场，它是极光电子加速的原因，对于地磁尾部的高度拉伸的场线配置，这是在亚暴爆发之前预计的，俯仰角平均值。计算了离子弹跳频率的值，结果表明，在距地球 15 Re 处，平均离子弹跳频率和磁漂移频率小于流体近似下获得的气球增长率。因此，动力学对气球不稳定性的影响是。然而，在距离地球 15 Re 以内，离子弹跳和磁漂移频率大于气球生长速率，因此，在距地球 15 Re 以外，动力学对气球不稳定性的影响很重要。

项目成果

Minimum energy state and minimum angle rotation of the magnetic field in a current sheet with shared magnetic field

具有共享磁场的电流片中磁场的最小能量状态和最小角度旋转

• 发表时间: 2002
• 作者: Akira Miura

Miura, A.: "Nonideal high-β magnetohydrodynamic Kelvin-Helmholtz instability driven by the shear in the ion diamagnetic drift velocity at the subsolar magnetopause"J.Geophys.Res. 108・A2. 5-1-5-8 (2003)

Miura, A.：“太阳下磁层顶离子反磁漂移速度剪切驱动的非理想高β磁流体动力学开尔文-亥姆霍兹不稳定性”J.Geophys.Res 108・A2 (2003)。

Validity of the fluid description of critical β and Alfven time scale of ballooning instability onset in the near-Earth collisionless high-β plasma

近地无碰撞高β等离子体中气球不稳定开始的临界β和阿尔文时间尺度的流体描述的有效性

• 发表时间: 2004
• 作者: Miura; A.
• 通讯作者: A.

Validity of the fluid description of critical β and Alfven time Scale of ballooning instability onset in the near-Earth collisionless high-β plasma

近地无碰撞高β等离子体中临界β和气球不稳定开始的阿尔文时间尺度的流体描述的有效性

• 发表时间: 2004
• 作者: Akira Miura

Miura, A.: "Validity of the fluid description of critical β and Alfven time scale of ballooning instability onset in the near-Earth collisionless high-β plasma"J.Geophys.Res.. 109,A02211. 1-14 (2004)

Miura, A.：“近地无碰撞高 β 等离子体中膨胀不稳定开始的临界 β 和阿尔文时间尺度的流体描述的有效性”J.Geophys.Res.. 109,A02211 (2004)。