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Polar stratospheric clouds can form at temperatures below about 195 K. Chemical reactions on the surfaces of the particles that form these clouds convert chlorine compounds from inert forms into highly reactive species. Figure Q10-2. Meanwhile, chlorine concentrations build up during the polar winter, and consequent ozone destruction is greatest when the sunlight returns in polar winter . PSCs appear in the lower stratosphere near the poles in winter. Though nacreous clouds are officially known as "polar stratospheric clouds", they are now common over Scotland, and have been observed as far south as the Midlands. These are best observed during winters in more northerly latitudes. PSCs form during winters in the Arctic and Antarctic stratospheres. Polar stratospheric clouds (PSCs) are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 m (49,000–82,000 ft). Polar stratospheric clouds create the conditions for drastic ozone destruction, providing … Lower average winter temperatures in the upper atmosphere might explain why nacreous clouds seem to be appearing with increased frequency and distribution. The nitric acid in polar stratospheric clouds reacts with chlorofluorocarbons to form chlorine, which catalyzes the photochemical destruction of ozone [3, 34]. Polar stratospheric clouds. Although polar stratospheric clouds can form in the Arctic, they rarely last long enough for extensive decreases in ozone. However, in general, it is neither as strong nor as cold as the one that forms in the Antarctic. Polar mesospheric clouds (PMCs) are a diffuse scattering layer of water ice crystals near the summer polar mesopause. The clouds Also known as nacreous clouds, these are the clouds that form in the winter polar stratosphere. Polar stratospheric clouds (PSCs) are common in … Arctic ozone decreases of as much as 40 percent have been measured. The polar vortex and polar stratospheric clouds exist only over Antarctica, which is why the ozone "hole" exists only there. During the continuously dark polar winter, the air inside the polar vortices becomes extremely cold, a necessary condition for polar stratospheric cloud formation. A polar winter vortex also forms in the Northern Hemisphere. Then, there is the formation of Polar Stratospheric Clouds (PSCs). This photo-graph of an Arctic polar stratospheric cloud (PSC) was taken from the ground at Kiruna, Sweden (67°N), on 27 January 2000. While the clouds look amazing, they can be potentially quite dangerous to our planet. They are best observed during civil twilight, when the Sun is between 1 and 6 degrees below the horizon, as well as in winter and in more northerly latitudes. Below: Dangerous beauty. "A 'warm' polar stratosphere is typically in the temperature range -73 o to -63 o C. Of course, as soon as the wave has dissipated, the polar region begins to cool down again." 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