nubbsgalore:photos by per andre hoffmann in antarctica of polar stratospheric clouds, so named bec
nubbsgalore: photos by per andre hoffmann in antarctica of polar stratospheric clouds, so named because they form fifteen miles above the earth; a hight which, given the curvature of the planet, allows them to be illuminated after sunset by light reflected from below the horizon. where the stratosphere is usually much too high for water molecules to remain stable and form clouds, the temperature in the antarctic winter season drops to such an extent that what sparse water molecules are present in the upper atmosphere condense from the pressure drop, forming wide stretches of thin clouds. unfortunately, these clouds also contain nitric acid, which reacts violently with chlorine released into the atmosphere by industrial processes elsewhere on the planet, causeng holes to form in the ozone layer. -- source link