Tuesday, July 03, 2007

Noctilucent clouds

Noctilucent clouds are spooky, silvery-blue clouds which shine at night. Like cirrus cloud, they're composed of ice crystals, but they form at such a high altitude that, during the Summer months at least, they can be seen even after the sun has set.
NASA's AIM satellite has just taken some images of noctilucent cloud distribution in the Northern hemisphere. It's claimed that the clouds are becoming brighter and more widespread, and one explanation for this is that the upper atmosphere may be cooling due to the energy being absorbed by increasingly abundant greenhouse gases in the lower atmosphere.

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