极光的形成
看到《从一到无穷大》里谈到“宇宙线簇射”，忽然想起当年在阿拉斯加看到的精灵般的极光，好像不也是“从星际空间射到大气层来的高能粒子”造成的吗？只知道是一种电离现象，但当时并没有深究。
于是上网搜了搜，发现那个“auroral zone”产生的原因相当有趣。感觉是太阳风吹到地球的表面，虽然大部分会被地球磁场形成的“护盾”屏蔽，但同时也会引起本来正常的地球磁力线来回震荡（大约每六分钟一次哦）。如此就导致另一面的磁尾像橡皮筋一样拉抻，一旦风云际会被从中折断，形成大小合适的闭合磁力线从而造成一种不稳定的状态，电子就会在两极附近的闭合路径上被加速沉降，同时与高空大气成分中的氧分子和氮分子等相互作用，释放出光子而点亮“auroral zone”的夜幕。
怪不得地球上只有特定的纬度能看到极光，太靠近两极磁力线不闭合或者闭合环太大，纬度太低磁场又不够强。当时看完了第一轮极光以为过几分钟还会出现，结果左等右等也不来，原来天上的分子们也在等下一回磁力线闭合好再次充电然后一起狂欢呢！
https://www.nasa.gov/feature/goddard/2016/nasa-s-themis-sees-auroras-move-to-the-rhythm-of-earth-s-magnetic-field
An artist’s rendering (not to scale) of a cross-section of the magnetosphere, with the solar wind on the left in yellow and magnetic field lines emanating from the Earth in blue. The five THEMIS probes were well-positioned to directly observe one particular magnetic field line as it oscillated back and forth roughly every six minutes. In this unstable environment, electrons in near-Earth space, depicted as white dots, stream rapidly down magnetic field lines towards Earth’s poles. There, they interact with oxygen and nitrogen particles in the upper atmosphere, releasing photons and brightening a specific region of the aurora.
模拟动画中截的风云际会的一瞬。
In this animation, the THEMIS mission observes auroral brightening – a result of a substorm, in which solar particles and energy disturb Earth’s magnetic field. The THEMIS orbit is shown in golden lines, while magnetic field lines emanating from Earth are shown in blue. When solar material impacts the magnetosphere, the day side contracts inward, while the back end, called the magnetotail, stretches out like a rubber band. When the stretched magnetotail finally snaps back, it starts to vibrate, much like a spring moving back and forth. In this unstable environment, electrons in near-Earth space rapidly stream down magnetic field lines towards Earth’s poles. There, they interact with oxygen and nitrogen particles in the upper atmosphere, releasing photons to create the aurora.
https://www.youtube.com/watch?v=lxWBlJ1kB7Q
于是上网搜了搜，发现那个“auroral zone”产生的原因相当有趣。感觉是太阳风吹到地球的表面，虽然大部分会被地球磁场形成的“护盾”屏蔽，但同时也会引起本来正常的地球磁力线来回震荡（大约每六分钟一次哦）。如此就导致另一面的磁尾像橡皮筋一样拉抻，一旦风云际会被从中折断，形成大小合适的闭合磁力线从而造成一种不稳定的状态，电子就会在两极附近的闭合路径上被加速沉降，同时与高空大气成分中的氧分子和氮分子等相互作用，释放出光子而点亮“auroral zone”的夜幕。
怪不得地球上只有特定的纬度能看到极光，太靠近两极磁力线不闭合或者闭合环太大，纬度太低磁场又不够强。当时看完了第一轮极光以为过几分钟还会出现，结果左等右等也不来，原来天上的分子们也在等下一回磁力线闭合好再次充电然后一起狂欢呢！
https://www.nasa.gov/feature/goddard/2016/nasa-s-themis-sees-auroras-move-to-the-rhythm-of-earth-s-magnetic-field
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An artist’s rendering (not to scale) of a cross-section of the magnetosphere, with the solar wind on the left in yellow and magnetic field lines emanating from the Earth in blue. The five THEMIS probes were well-positioned to directly observe one particular magnetic field line as it oscillated back and forth roughly every six minutes. In this unstable environment, electrons in near-Earth space, depicted as white dots, stream rapidly down magnetic field lines towards Earth’s poles. There, they interact with oxygen and nitrogen particles in the upper atmosphere, releasing photons and brightening a specific region of the aurora.
模拟动画中截的风云际会的一瞬。
 |
In this animation, the THEMIS mission observes auroral brightening – a result of a substorm, in which solar particles and energy disturb Earth’s magnetic field. The THEMIS orbit is shown in golden lines, while magnetic field lines emanating from Earth are shown in blue. When solar material impacts the magnetosphere, the day side contracts inward, while the back end, called the magnetotail, stretches out like a rubber band. When the stretched magnetotail finally snaps back, it starts to vibrate, much like a spring moving back and forth. In this unstable environment, electrons in near-Earth space rapidly stream down magnetic field lines towards Earth’s poles. There, they interact with oxygen and nitrogen particles in the upper atmosphere, releasing photons to create the aurora.
https://www.youtube.com/watch?v=lxWBlJ1kB7Q
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