Twenty Questions and Answers About the Ozone Layer: 2010 Update
Scientific Assessment of Ozone Depletion: 2010
World Meteorological Organization Global Ozone Research and Monitoring Project - Report No. 52
National Oceanic and Atmospheric Administration
National Aeronautics and Space Administration
United Nations Environment Programme
World Meteorological Organization
Additional Topics: The 2002 Antarctic Ozone Hole
The 2002 Antarctic ozone hole showed features that looked surprising at the time (see Figure Q11-4 in Q11: How severe is the depletion of the Antarctic ozone layer? ). It had much less ozone depletion as measured by the area of the ozone hole or minimum total-ozone amounts in comparison with the 2001 ozone hole. The 2002 values now stand out clearly in the year-to-year changes in these quantities displayed in Figure Q11-2 in Q11: How severe is the depletion of the Antarctic ozone layer? . There were no forecasts of an ozone hole with unusual features in 2002 because the chemical and meteorological conditions required to deplete ozone, namely low temperatures and available reactive halogen gases, were present that year and did not differ substantially from previous years. The ozone hole initially formed as expected in August and early September 2002. Later, during the last week of September, an unexpected and surprisingly strong meteorological event occurred that dramatically reshaped the ozone hole into two separate depleted regions. As a result of this disturbance, the combined area of these two regions in late September and early October was significantly less than that observed for the previous or subsequent ozone holes.
The unexpected meteorological influence in 2002 resulted from specific atmospheric air motions that sometimes occur in polar regions. Meteorological analyses of the Antarctic stratosphere show that it was warmed by very strong, large-scale weather systems that originated in the lower atmosphere (troposphere) at midlatitudes in late September. At that time, Antarctic temperatures are generally very low (see Q10: Why has an "ozone hole" appeared over Antarctica when ozone-depleting substances are present throughout the stratosphere? ) and ozone destruction rates are near their peak values. The influence of these tropospheric systems extended poleward and upward into the stratosphere, disturbing the normal circumpolar wind flow (polar vortex) and warming the lower stratosphere where ozone depletion was ongoing. Higher temperatures reduced the rate of ozone depletion and led to the higher minimum values observed for total ozone in Figure Q11-2 in Q11: How severe is the depletion of the Antarctic ozone layer? . The higher-than-normal impact of these weather disturbances during the critical time period for ozone loss reduced the total loss of ozone in 2002.
The strong influence of the 2002 warming event is unique in the many decades of Antarctic meteorological observations. Another warming event occurred in 1988 causing smaller changes in the ozone hole features in Figure Q11-2 in Q11: How severe is the depletion of the Antarctic ozone layer? . Large warming events are difficult to predict because of the complex conditions leading to their formation.
In 2003 through 2009, ozone hole features returned to values observed from the mid-1990s to 2001 (see Figure Q11-2 in Q11: How severe is the depletion of the Antarctic ozone layer? ). The high ozone depletion found since the mid-1990s, with the exception of 2002, is expected to be typical of coming years. A significant, sustained reduction of Antarctic ozone depletion, leading to full recovery of total ozone, requires comparable, sustained reductions of ODSs in the stratosphere. Even with the source gas reductions already underway (see Q16: Has the Montreal Protocol been successful in reducing ozone-depleting substances in the atmosphere? ), the return of Antarctic total ozone to 1980 values is not expected to occur before 2050.