A polar winter vortex also forms in the Northern Hemisphere. 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. The clouds Arctic ozone decreases of as much as 40 percent have been measured. However, in general, it is neither as strong nor as cold as the one that forms in the Antarctic. These beautiful images of polar stratospheric clouds were taken over Tromso City in Norway. During the continuously dark polar winter, the air inside the polar vortices becomes extremely cold, a necessary condition for polar stratospheric cloud formation. Description. Below: Dangerous beauty. Polar stratospheric clouds (PSCs) are common in … The nitric acid in polar stratospheric clouds reacts with chlorofluorocarbons to form chlorine, which catalyzes the photochemical destruction of ozone [3, 34]. Figure Q10-2. 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. Although polar stratospheric clouds can form in the Arctic, they rarely last long enough for extensive decreases in ozone. 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. This photo-graph of an Arctic polar stratospheric cloud (PSC) was taken from the ground at Kiruna, Sweden (67°N), on 27 January 2000. The polar vortex and polar stratospheric clouds exist only over Antarctica, which is why the ozone "hole" exists only there. This means more dangerous UV radiation will reach the Earth's surface. 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. While the clouds look amazing, they can be potentially quite dangerous to our planet. The particles grow from the con-densation of water and nitric acid (HNO3). Polar stratospheric clouds (PSCs) are the exception. Then, there is the formation of Polar Stratospheric Clouds (PSCs). "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." Lower average winter temperatures in the upper atmosphere might explain why nacreous clouds seem to be appearing with increased frequency and distribution. Polar mesospheric clouds (PMCs) are a diffuse scattering layer of water ice crystals near the summer polar mesopause. 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