| The extremely cold temperatures of the stratosphere during the polar winter enable the development of polar stratospheric clouds. |
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| These polar stratospheric clouds form only in regions of very low temperature and as a result the clouds only exist in winter stratospheric polar regions. |
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| Some of the extraterrestrial material could be incorporated into polar stratospheric clouds over Antarctica and sediment out of the lower stratosphere. |
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| The presence of trace amounts of nitric and sulfuric acids enables the formation of polar stratospheric clouds a few degrees above the frost point. |
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| A wetter and colder stratosphere means more polar stratospheric clouds, which is likely to lead to more severe ozone loss in both polar regions. |
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| The chemical reactions that break down ozone are particularly intense within cold, acidified clouds called polar stratospheric clouds. |
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| Such a cooling could increase the formation of polar stratospheric clouds, causing Arctic ozone depletion to become even more severe. |
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| That triggered vast polar stratospheric clouds, some of them as big as the continental United States. |
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| During the Arctic winter, cool temperatures in the stratosphere form polar stratospheric clouds. |
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| Extreme cold permits chemical reactions to take place between the polar stratospheric clouds and chlorofluorocarbons, releasing ozone-destroying chlorine. |
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| The Arctic stratosphere temperature remained warmer than normal for much of the winter, limiting the formation of polar stratospheric clouds that act as a catalyst in Arctic ozone depletion. |
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| Higher concentrations of these gases may have the effect of prolonging the recovery of the ozone layer, mainly through their effects on stratospheric cooling and the formation of polar stratospheric clouds. |
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| But in polar regions during winter seasons, cold stratospheric temperatures can cause the formation of polar stratospheric clouds that enhance the rate of O3 depletion. |
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| Of particular importance is the effect of temperature on the formation of polar stratospheric clouds, and the enhancement that these cause of chlorine concentration and ozone destruction. |
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| Key chemical reactions that lead to ozone depletion happen on the surface of rare polar stratospheric clouds, which form high up in the atmosphere. |
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| Polar stratospheric clouds, which drive ozone loss in Antarctica, turned up in force during the most recent Arctic winter. |
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