An outbreak of polar stratospheric clouds (PMCs) is underway around the Arctic Circle. Unlike normal grey-white clouds, which hug Earth's surface at altitudes of only 5 to 10 km, PMCs float through the stratosphere (25 km) and they are fantastically colorful. Sarah Skinner saw this specimen high above Abisko, Sweden:
"Just as I was heading out to de-ice the car on Dec. 14th, I looked up and noticed the most incredible cloud formation," says Skinner. "At the same time, an excited text came through from my boss, aurora tour guide Chad Blakley, who having lived here for many years has seen this only once or twice and explained to an Arctic newbie like me how rare these formations really are."
Also known as "nacreous" or "mother of pearl" clouds, the icy structures form in the lower stratosphere when temperatures drop to around minus 85ºC. Sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors by diffraction and interference. Once thought to be mere curiosities, some PMCs are now known to be associated with the destruction of ozone.
"Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world," writes atmospheric optics expert Les Cowley. "Once seen they are never forgotten." www.spaceweather.com
Also known as "nacreous" or "mother of pearl" clouds, the icy structures form in the lower stratosphere when temperatures drop to around minus 85ºC. Sunlight shining through tiny ice particles ~10µm across produce the characteristic bright iridescent colors by diffraction and interference. Once thought to be mere curiosities, some PMCs are now known to be associated with the destruction of ozone.
"Nacreous clouds far outshine and have much more vivid colours than ordinary iridescent clouds, which are very much poor relations and seen frequently all over the world," writes atmospheric optics expert Les Cowley. "Once seen they are never forgotten." www.spaceweather.com
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