太阳风状态参数的变化对地球磁鞘中磁场起伏特性的影响

本文利用MHD激波跳跃条件的精确解,具体讨论了行星际背景太阳风状态参数Alfvén马赫数M₁、等离子体β₁参数和磁场角θ₁的变化对地球磁鞘区中磁场起伏特性及其分布的影响.主要结果是:马赫数M₁的变化主要控制磁场起伏特性:放大倍数、相对起伏和各向异性程度的水准高低.磁场角θ₁的变化控制磁场起伏的空间分布特性.等离子体β₁参数的变化,不引起磁场起伏特性的明显变化(对于实际经常发生的情况M₁ 8而言).M₁、θ₁是强控制参数,而β₁是弱控制参数;磁鞘区磁场起伏对太阳风状态参数的变化响应呈现明显的晨-昏不对称性(行星际磁场位于黄道面时),响应主要发生在晨侧.晨侧的磁场起伏(或湍动)相当活跃,而昏侧相当稳定;磁鞘中不同地点磁场起伏特性对太阳风状态参数M₁、β₁的变化响应有大致相同的形式,而对其磁场角度θ₁的变化却有迥然不同的形式. 

INFLUENCES OF THE VARIATIONS OF SOLAR WIND STATE ON THE MAGNETIC FIELD FLUCTUATION CHARACTERISTICS IN EARTH'S MAGNETOSHEATH

Influences of the variations of the background solar wind parameters, Alfvenic Mach number M₁, plasma β₁ value and magnetic field angle 61, on the state and spatial distribution of the magnetic field fluctuations in the Earth's magnetosheath are discussed using the exact solution of MHD shock wave jump conditions. The results show that: (1) M₁ mainly controls the level of the amplitude, the relative fluctuation and the anisotropic degree of magnetic field fluctuations. θ₁ controls the spatial distribution of magnetic field fluctuation characteristics. β₁ value does not produce obvious variations of the state of magnetic field fluctuations; (2) While the state of background solar wind changes, the variations of the state of magnetic field fluctuations behind the bow shock will be asymmetric, this responses to the change of background solar wind parameters, M₁, β₁, almost only occur in the dawn side of the magnetosheath. The dawn side is very active in the fluctuations or turbulences of magnetic field, but the dusk side is stable; and (3) This responses to M₁,β₁ at different places are similar, but to θ₁ parameter, the responses show very different form.