Sunward propagating Pc5 waves observed on the post-midnight magnetospheric flank
Sunward propagating Pc5 waves observed on the post-midnight magnetospheric flank
复制标题
DOI：
10.5194/angeo-26-1567-2008
复制
发表时间：
2008-01-01
影响因子：
1.9
通讯作者：
Glassmeier, K. -H.
中科院分区：
文献类型：
--
作者：
Eriksson, P. T. I.;Blomberg, L. G.;Glassmeier, K. -H.
对环形Pc 5波驱动器的总体关注一直是位于或作用于磁层昼侧磁层顶和昼侧侧翼的过程。这些过程可以产生在磁层中向尾部传播的波。然而，越来越多的研究，无论是理论还是实验，都着眼于向太阳传播的波，这是由磁尾中的过程引起的。在这里，我们提出了一个超低频（ULF）波在午夜后/上午部门的磁层在L=16 R-E。波具有环形模式偏振。我们估计的方位波数为m=3，符合环形模式型脉动。正号表示波是向太阳传播的，这一点可以通过波的坡印亭通量得到证实。波的频率并不随时间而恒定，而是在事件开始时显示出小的增加，高达2.0 mHz以上。然后频率降低到1.0 mHz。这种减少与总磁场强度的下降相吻合，我们推测这是否与观察到的行星际磁场（IMF）的符号反转有关。这一事件发生在相对平静的磁层条件下，太阳风速度约为400公里/秒。因此，这一事件很可能是由磁尾中的源驱动的，并且频率的变化是一个很好的例子，即ULF波的频率可以通过谐振场线上的等离子体参数的变化来调制。
The overall focus on the driver of toroidal Pc5 waves has been on processes located at or acting on the dayside magnetopause and dayside flanks of the magnetosphere. These processes can generate waves that propagate tailward in the magnetosphere. However, an increasing number of studies, both theoretical and experimental, have looked at waves propagating sunward and that are caused by processes in the magnetotail. Here we present an ultra low frequency (ULF) wave observed in the post-midnight/morning sector of the magnetosphere at L=16 R-E. The wave has a toroidal mode polarization. We estimate the azimuthal wave number to m=3, consistent with a toroidal mode type pulsation. The positive sign indicates that the wave is propagating sunward and this is confirmed by looking at the Poynting flux of the wave. The frequency of the wave is not constant with time but shows a small increase in the beginning of the event up to over 2.0 mHz. Then the frequency decreases to 1.0 mHz. This decrease coincides with a drop in the total magnetic field strength and we speculate if this is related to an observed reversal of the sign of the interplanetary magnetic field (IMF) By-component. This event occurs during relatively quiet magnetospheric conditions with a solar wind speed of approximately 400 km/s. Thus this event is highly likely to be driven by a source in the magnetotail and the change in frequency is an excellent example that the frequency of an ULF wave may be modulated by changes of the plasma parameters on the resonant field line.