行星际起伏向磁层顶的输运

时间尺度为分钟数量级的太阳风速度和行星际磁场大幅度扰动实际上始终存在于行星际空间的。这些扰动一直传输到紧贴磁层边界面外侧的区域。它们在磁鞘等离子体和磁层顶的相互作用过程中可能起很重要的作用。行星际起伏中的磁场分量在通过地球弓激波时首先经历一次跳跃,然后一部分扰动被带到磁层边界面处。在边界面附近磁场扰动幅度被大大地放大了。弓激波上游的太阳风条件控制了放大因子。本文所作的数值模拟研究结果表明,如果上游有大幅度的扰动,在边界面附近就有大幅度的Alfven起伏的磁场分量。当上游磁场接近垂直于日地联线时,放大因子变得相当大,而且放大因子随上游的等离子体β值和/或Alfven马赫数的增加而增加。上游各向异性对放大因子的影响不大。在磁层边界附近存在大幅度起伏表明这里不存在稳定的片流。 

Transport of the Interplanetary Fluctuations to the Magnetopause

Fluctuations in solar wind velocity and magnetic field or relatively large amplitude on a time scale of the order of minutes are presented in interplanetary space essentially all the time.These fluctuations are transported to the region immediately outside the boundary surface of the magnetosphere.They may play an important role in the interaction of the magnetosheath plasma with the magnetopause.The interplanetary fluctuations first make a jump across the earth's bow shock.After the jump,some fluctuations are carried to reach the boundary surface of the magnetosphere.The amplitude of fluctuations at the surface of the magnetosphere is considerably amplified as compared with the interplanetary fluctuations.The solar wind conditions upstream of the bow shock control over the amplification factor This simulation study suggests that large Alfvenic fluctuations are presented at the boundary surface of the magnetosphere if the upstream fluctuations are large.The amplification factor becomes very large when the upstream magnetic field is nearly perpendicular to the sun-earth line and the amplification factor also increases with incressing plasma beta value and/or increasing Alfvenic Mach number.The effect of the state of upstream anisotropy on the amplification factor is relatively small.The present of large fluctuations indicates that no steady laminar flow exists in the boundary layer of the magnetosphere.