Noctilucent or “night-shining” clouds, which appear sometime in late spring and last until the near the end of summer above the Earth’s polar regions, are the highest clouds in our planet’s atmosphere, floating nearly 50 miles (80 kilometers) above the surface.
They’re very cold and filed with tiny ice crystals, which when illuminated by sunbeams, turn into a glowing electric-blue.
That’s all pretty strange, but what’s even stranger is that they seem to be a relatively recent phenomenon in the Earth’s atmospheric history.
The first sighting of them was in 1885, two years after the massive eruption of the Indonesian volcano Krakatoa. 19th-century scientists originally believed that they were caused by volcanic ash in the atmosphere.
But after the ash settled, oddly, the noctilucent clouds didn’t go away. Instead, they’ve actually gotten brighter and become more common. They’ve also started appearing further south, with sightings in places such as Utah and Colorado. NASA says this could be a sign of the increasing greenhouse gases in the Earth’s atmosphere.
This year, the northern clouds also arrived a bit earlier than usual. NASA’s Aeronomy of Ice in the Mesosphere (AIM) satellite spotted what the agency’s website calls “a luminous patch of electric-blue” drifting across the Arctic Circle on May 19.
One interesting question about the northern noctilucent clouds is whether their behavior will shift.This year’s noctilucent clouds in the Southern Hemisphere were much more variable than usual, with a big drop off in cloud frequency 15 to 25 days after the summer solstice. That’s the time when they usually are most abundant.
The Guardian newspaper reports that scientists think this may be the result of altered conditions in the upper atmosphere, but nobody knows yet exactly what those changes are or what they mean.
Read more at Discovery News
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