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Characteristics of Diamagnetic Hydromagnetic Waves in a High-beta Model Magnetosphere

高β模型磁层中反磁性水磁波的特征

基本信息

批准号：
60460051
负责人：
TAMAO Tsutomu
金额：
$ 4.48万
依托单位：
Faculty of Science, University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1985
资助国家：
日本
起止时间：
1985 至 1986
项目状态：
已结题

项目摘要

A linear eigenmode analysis of drift Alfven wave is performed in a curved magnetic field configuration in a high- <beta> plasma to find a generation mechanism of diamagnetic stormtime Pc5 pulsation characterized by a large azimuthal mode number (m>50). A magnetic field line obtained from a self-consistent model of magnetic field and plasma pressure is tied to a conducting ionosphere. An eigenmode equation is solved along the field line in order to obtain the eigenfrequency and eigenmode structure of the drift Alfven wave. In the absence of the coupling to the drift wave all obtained modes (poloidal oscillations modified by high- <beta> effect) are stable or weakly damped oscillations except for the fundamental mode. The fundamental mode becomes unstable to the ballooning instability driven by the unfavorable magnetic field curvature and is an aperiodic oscillation with zero real frequency. The eigenmode of the unstable mode is confined near the equator and the plasma pressure and magne … More tic pressure are almost out of phase. When the unstable mode is coupled to the drift wave, the unstable mode has a real frequency determined by a diamagnetic drift speed. The detailed results of the linear eigenmode analysis for both the ballooning interchange and drift Alfven modes in a model magnetosphere are described, and their implications to the origin of the stormtime pulsations are discussed. The obtained wave period of 270 sec for the drift Alfven mode with the azimuthal mode number m=50, its westward propagation and diamagnetic relationship between the perturbed magnetic and gas pressures suggest us that the unstable drift Alfven wave is the strong candidate for the observed stormtime Pc5 pulsations. By applying the adiabatic particle picture with a finite Larmor radius effect, we have extended our analysis to include a linear mode coupling between the shear (drift) Alfven and the slow magnetosonic waves under the curved field line configuration. Numerical solutions for such coupling oscillations in a model ring current region yield a fundamental mode of standing oscillations along a curved field line with a linear growth rate much larger than the real frequency of the average ion drift motion. It has been shown that the finite Larmor radius effect in the drift motion of ions has a stabilizing tendency as the perpendicular wavelength becomes short. Less

本文对弯曲磁场位形下的漂移Alfven波进行了线性本征模分析<beta>，以寻找以大方位模数（m>50）为特征的反磁暴时Pc5脉动的产生机制。从磁场和等离子体压力的自洽模型得到的磁场线被绑定到导电电离层。为了得到漂移阿尔芬波的本征频率和本征模结构，沿着场线求解本征模方程。在没有与漂移波耦合的情况下，除基模外，所有获得的模式（由高效应修改的极向振荡<beta>）都是稳定的或弱阻尼的振荡。在不利的磁场曲率驱动下，基模变得不稳定为气球不稳定，并且是具有零真实的频率的非周期振荡。不稳定模的本征模被限制在赤道附近，等离子体的压力和磁场 ...更多信息脉动压力几乎不同步。当不稳定模式耦合到漂移波时，不稳定模式具有由抗磁漂移速度确定的真实的频率。详细的结果的线性本征模分析的气球交换和漂移阿尔芬模式在模型磁层的描述，并讨论了它们的影响的起源的暴时脉动。方位角模数m=50的漂移Alfven模的波周期为270秒，它的向西传播和扰动磁压与气压之间的反磁关系表明，不稳定的漂移Alfven波是观测到的暴时Pc5脉动的强有力的候选者。通过应用绝热粒子图片与有限的拉莫尔半径效应，我们已经扩展了我们的分析，包括剪切（漂移）阿尔芬和慢磁声波弯曲场线配置下的线性模式耦合。在一个模型环电流区域的这种耦合振荡的数值解产生一个基本模式的驻波振荡沿着一个弯曲的场线与线性增长率远大于平均离子漂移运动的真实的频率。结果表明，当垂直波长变短时，离子漂移运动中的有限拉莫尔半径效应有稳定化的趋势。少