Frequency‐doubled density perturbations driven by ULF pulsations
Frequency‐doubled density perturbations driven by ULF pulsations
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ULF 脉动驱动的倍频密度扰动
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
J. Wanliss
中科院分区：
文献类型：
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作者：
I. Mann;G. Chisham;J. Wanliss
我们展示了主动磁层粒子示踪探测器离子释放模块 (AMPTE IRM) 对 1984 年 10 月 28 日世界标准时间 0915 至 1030 年间压缩 Pc5 ULF 振荡波包的观测。这些波是在当地早晨在赤道平面附近观测到的，其主周期约为 380 秒，并且很可能具有基本的场对齐谐波结构。这些波以前被解释为向下传播的磁层波导模式[Mann et al., 1998]。在波的最大幅度时，AMPTE IRM 观察到背景密度的振荡，其频率是同时发生的 ULF 脉动的两倍。我们发展了一种理论，解释了非绝热背景等离子体压力分布中弯曲通量管的大幅径向位移所产生的倍频密度涨落。该理论预测径向速度场的波峰和波谷与 AMPTE IRM 观测到的倍频密度振荡的波峰之间存在锁相。观察结果有力地支持了这样的假设：倍频是由于有限幅度效应而发生的。
We present Active Magnetospheric Particle Tracer Explorers Ion Release Module (AMPTE IRM) observations of a wave packet of compressional Pc5 ULF oscillations between 0915 and 1030 UT on October 28, 1984. The waves are observed in the local morning near the equatorial plane, have a dominant period of ∼ 380 s, and most probably have a fundamental field-aligned harmonic structure. The waves have previously been interpreted as a magnetospheric waveguide mode propagating downtail [Mann et al., 1998]. At the time of the maximum amplitude of the waves, AMPTE IRM observes oscillations in the background density at a frequency twice that of the coincident ULF pulsations. We develop a theory which explains the generation of frequency-doubled density fluctuations through large-amplitude radial displacements of curved flux tubes in a nonadiabatic background plasma pressure distribution. The theory predicts a phase locking between the peaks and troughs of the radial velocity field and the peaks in the frequency-doubled density oscillations which is observed by AMPTE IRM. The observations strongly support the hypothesis that the frequency doubling occurs as a result of finite amplitude effects.