Otherwise known as polar stratospheric clouds, PSCs, these striking images occur at FL 360 to 720 in extreme arctic cold, around 195K (-78deg Centigrade). These cloud pictures result from particles in the atmosphere. They also warn of extreme cold weather altimeter error and now possible ozone holes in the Arctic.[1] I wonder what implications for military or commercial pilots flying a polar rout at these altitudes. I would think the military helmet visor with complete peripheral protection against infra red would be sufficient, never mind the cosmic. Airline captains might consider goggles with peripheral protection in place of sun glasses and possibly closing the passenger window shades. Look out for the mountains below. "The mountains grow taller in the winter in Alaska and the arctic!"
"Scientists recently discovered that polar stratospheric clouds, long known to play an important role in Antarctic ozone destruction, are occurring with increasing frequency in the Arctic. These high altitude clouds that form only at very low temperatures help destroy ozone in two ways—they provide a surface which converts benign forms of chlorine into reactive, ozone-destroying forms, and they remove nitrogen compounds that moderate the destructive impact of chlorine. In recent years the atmosphere above the Arctic has been colder than usual, and polar stratospheric clouds have lasted into the spring. As a result, ozone levels have been decreasing.[2
[2] NASA http://www.giss.nasa.gov/research/features/200402_tango/
[1] Nature 478, 469-475 (2011) Gloria l. Manney et al.
[3]Upper photo:http://www.nature.com/nature/journal/v478/n7370/full/478462a.html
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