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

用弯曲磁场位形对高β等离子体中漂移Alfven波的线性本征模进行了分析，找出了以大方位模数(m&gt；50)为特征的抗磁风暴时Pc5脉动的产生机制。从磁场和等离子体压力的自洽模型获得的磁力线被绑在导电电离层上。沿场线求解本征模方程，得到漂移Alfven波的本征频率和本征模结构。在没有与漂移波耦合的情况下，除基模外，所有获得的模式(经高β效应修正的极向振荡)都是稳定的或弱衰减的振荡。在不利的磁场曲率驱动下，基模对气球不稳定性变得不稳定，是一种零实频率的非周期振荡。不稳定模的本征模局限在赤道附近，等离子体气压和磁力…附近。更多的TiC压力几乎是异相的。当不稳定模耦合到漂移波时，不稳定模具有由抗磁漂移速度确定的实频率。给出了模型磁层中气球交换模和漂移Alfven模的线性本征模分析的详细结果，并讨论了它们对风暴脉动起源的影响。方位角模数m=50的漂移Alfven波的周期为270秒，它向西传播，扰动磁压和气压之间的反磁关系表明，不稳定的漂移Alfven波是观测到的风暴时间Pc5脉动的强烈候选者。通过应用有限Larmor半径效应的绝热粒子图像，我们将我们的分析扩展到包括弯曲场形下剪切(漂移)Alfven波和慢磁声波之间的线性模耦合。模型环电流区这种耦合振荡的数值解产生沿弯曲场线的驻波基模，其线性增长率远大于平均离子漂移运动的真实频率。结果表明，离子漂移运动中的有限拉莫半径效应随着垂直波长的变短而趋于稳定。较少

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