Climate Fact: The Ozone Hole and Climate
Near the center of Antarctica in the polar vortex, strong westerly winds that blow in a circle around the continent during winter trap an envelope of air near the South Pole, prohibiting this air from mixing with warmer air masses closer to the equator. The extreme cold in the vortex causes clouds to form in the lower part of the stratosphere. Conditions in these stratospheric clouds are just right for a complex series of chemical reactions to take place, resulting in the destruction of ozone molecules and the formation of the ozone hole. This hole is at its maximum during the austral (Southern Hemisphere) spring months of September through December; stratospheric ozone concentrations during these months can fall by 33 percent. Once temperatures warm sufficiently, the strong westerly winds slow and the polar vortex breaks up, allowing ozone rich air to blow in and ozone poor air to blow out. This movement of ozone poor air is noticeable in parts of New Zealand and South America, where ozone concentrations can temporarily drop by 10 percent.
While the vortex is a local phenomenon, the strength and annual duration of the westerly winds that create the polar vortex are influenced by a larger phenomenon called the Southern Annular Mode (SAM), the difference in atmospheric pressure between 40 and 65 degrees South. When this difference is relatively large, the westerly winds around Antarctica are particularly strong, leading to a stronger vortex and more ozone destruction. High concentrations of ozone, however, can affect the movements of air between the stratosphere and troposphere, ultimately affecting the SAM itself. Better understanding this “coupling” between the SAM and the ozone hole will be needed for better weather and climate prediction, as well as for predicting future ozone concentrations.
Seasons: Winter, Spring, Summer, Fall
Sources: Sparling, B. “The Antarctic Ozone Hole.” NAS Educational Resources. 2001. Accessed Online 10 January 2009