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The Antarctic Vortex
So far, only the vortex area has been studied. The geographical area within suitable PV contours, depending on the level, has been calculated for every day from May through December for all the years from 1979 up to present, excluding 1994, for which no data was available. Monthly means for the months September through December have been made and are shown in the plots below. The study has been carried out for the isentropic levels 400, 425, 450, 475, 500 and 550 K. The PV limits for the levels are chosen as: -16, -22, -30, -34, -50 and -78 PVU, respectively.
Daily Vortex Areas
Time series of the vortex area at various levels have been calculated and are presented in Figure 9. It can be seen from these figures that the vortex area in September reached a size never reached before in the 1990s.
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Figure 9. Daily values of the vortex area during the 1990s for the levels 400 (upper left), 450 (upper right), 500 (lower left) and 550 K (lower right).
Monthly means
Monthly average values of the vortex area has been calculated for several levels and for the months Sept. - Dec. Figures 10-13 show the development of the vortex area at 400, 450, 500 and 550 K from 1979 to present. Table 2 shows the trend values with their one sigma uncertainties.
Figure 10. Monthly mean values of the vortex area at 400 K. The month of
October has been omitted since it looks quite similar to September.
Figure 11. Monthly mean values of the vortex area at 450 K. The month of
October has been omitted since it looks quite similar to September.
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Table 2. Linear trends (% per year) in the monthly mean vortex area for the south polar vortex |
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| Level/Month | Sep | Oct | Nov | Dec |
| 400 | -0.5 ± 0.3 | 0.2 ± 0.3 | 1.8 ± 0.5 | 7.8 ± 1.3 |
| 425 | 0.0 ± 0.3 | 0.2 ± 0.3 | 2.3 ± 0.6 | 8.4 ± 1.5 |
| 450 | 0.4 ± 0.2 | 1.0 ± 0.3 | 2.2 ± 0.6 | 9.5 ± 2.3 |
| 475 | -0.1 ± 0.2 | 0.3 ± 0.3 | 2.0 ± 0.6 | 9.4 ± 2.3 |
| 500 | -0.3 ± 0.2 | 0.8 ± 0.3 | 6.7 ± 1.5 | 17.9 ± 4.4 |
| 550 | -0.4 ± 0.2 | 0.3 ± 0.3 | 3.8 ± 1.1 | 14.2 ± 4.3 |