However ozone values have also not recovered to their higher 1980 values. The implication of these changes needs to be examined in the context of changes in amounts of ozone depleting gases in the atmosphere and varying meteorological conditions. High ozone extends over the entire Arctic region. The 1979 to 1986 base period is chosen because 1979-1986 average values are indicative of the early data record. Most notable are the positive anomalies of more than 12 percent over the Arctic region.
Negative anomalies appear throughout middle latitudes.
Temperatures in the lower stratosphere are closely coupled to ozone through dynamics and photochemistry. At the end of January, temperatures increased markedly at 50 hPa, in association with a large stratospheric warming. Without the extremely low temperatures, enhanced ozone destruction would not occur. Figure 8 compares the average 100 hPa temperature in the polar region for each March of the last 23 years with the date the stratospheric polar vortex diminished below a specific threshold size. March 2001 was among the years with the shortest duration of the polar vortex and with the highest average temperatures.