多彩光柱 ~太陽光柱~

Colorful Light Pillars

影像版權與提供: Walter Tape (Alaska Fairbanks), Figure 8-1, Atmospheric Halos

Explanation:
How can an aurora appear so near the ground? Pictured above are not
aurora but nearby light pillars, a local phenomenon that can appear as a
distant one. In most places on Earth, a lucky viewer can see a Sun-pillar, a
column of light appearing to extend up from the Sun caused by flat
fluttering ice-crystals reflecting sunlight from the upper atmosphere.
Usually these ice ice crystals evaporate before reaching the ground. During
freezing temperatures, however, flat fluttering ice crystals may form near
the ground in a form of light snow, sometimes known as a crystal fog. These
ice crystals may then reflect ground lights in columns not unlike a
Sun-pillar. In the above picture, the colorful lights causing the light
pillars surround a ice-skating rink in Fairbanks, Alaska.

說明:
這極光看起來怎會如 此靠近地平面呢? 上圖的影像可不是極光，而是附近的光柱，是個看似遙遠卻只不過是地區性的現象。
在大部分地區，只要夠幸運，民眾有可能看到太陽光柱，一道從太陽延伸出來的光柱，這是飄動的扁平冰晶反射來自高空的陽光所致。
通常這些冰晶在落至地面前就蒸發了，不過，在極為嚴寒的溫度下，這些飄動的扁平冰晶會在地面附近形成薄雪的型式，有時被稱為冰晶霧。
於是這些冰晶就會將地面上的燈光反射出柱狀光柱，就像太陽光柱般。 上圖中，造成光柱的彩色燈光環繞著美國．阿拉斯加州費爾班克斯市(Fairbanks)
的溜冰場。

資料來源: Scientific American Department of Physics, NCKU