Ultra Low Frequency Waves in the Magnetosphere
Ultra Low Frequency Waves in the Magnetosphere
复制标题
磁层中的超低频波
DOI：
10.1007/978-3-540-46315-3_16
复制
发表时间：
2007
期刊：
影响因子：
3.7
通讯作者：
U. Villante
中科院分区：
文献类型：
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作者：
U. Villante
地磁脉动（或更简单地称为“磁脉动”）是在磁层中传播的超低频（ULF）磁流体波的地面表现。最初被称为“微脉动”，它们首先由Celsius（1741年，他将乌普萨拉的罗盘测量与极光波动进行了比较），Nervander（1840年）和Stewart（1859年）发现。五十多年前，邓吉（1967）认为微脉动可以用在地磁场线上激发的阿尔文波来解释。事实上，它们独特的周期性使得邓吉提出了一种解释，即磁脉动是在两个半球的电离层之间反射的驻波。磁脉动的起源是行星际介质，在磁层中，也可能是在太阳本身。然而，在地面上探测到的波与进入磁层的波并不相同：实际上，波的能量经过几个过程转换，地面信号是电磁波撞击电磁波在电离层中感应出的电流辐射出的电磁波。地面脉动的性质还取决于观测者下方地球的电导率。
Geomagnetic (or more simply" magnetic") pulsations are the ground manifestation of ultra low frequency (ULF) hydromagnetic waves propagating in the magnetosphere. Originally termed “micropulsations", they were first identified by Celsius (who compared compass measurements in Uppsala with auroral fluctuations, 1741), by Nervander, 1840's and by Stewart, 1859. More than fifty years ago, Dungey (1967) argued that micropulsations could be interpreted in terms of Alfvén waves excited on geomagnetic field lines. In fact, their distinct periodicity led Dungey to suggest an interpretation of magnetic pulsations in terms of standing waves reflecting between ionospheres of opposite hemispheres.The origin of magnetic pulsations is in the interplanetary medium, in the magnetosphere and, possibly, on the Sun itself. However, waves detected on the ground are not the same waves that enter the magnetosphere: indeed, wave energy is transformed by several processes, and ground signals are electromagnetic waves radiated from currents induced in the ionosphere by the impinging hydromagnetic waves. The properties of ground pulsations also depend on the conductivity of the Earth underneath the observer.