Variability of the total ozone trend over Europe for the period 1950?2004 derived from reconstructed data
Résumé
Long-term variability of total ozone over Europe is discussed using results of a flexible trend model applied to the reconstructed total ozone data for the period 1950?2004. The data base used was built within the objectives of the COST action 726 "Long-term changes and climatology of UV radiation over Europe". The trend pattern, which comprises both anthropogenic and "natural" component, is not a priori assumed but it is a result of a smooth curve fit to the zonal monthly means and monthly grid values. The trend values in 5-year and 10-year intervals in cold (October-next year April) and warm (May?September) seasons are calculated as the differences between the smooth curve values at the end and beginning of selected time intervals divided by length of the intervals. The confidence intervals for the trend values are calculated by the block bootstrapping. The statistically significant negative trends are found almost over whole Europe only in the period 1985?1994. Negative trends up to ?3% per decade appeared over small areas in earlier periods when the anthropogenic forcing on the ozone layer was weak. The statistically positive trends are found only during warm seasons 1995?2004 over Svalbard archipelago. The reduction of ozone level in 2004 relative to that before the satellite era is not dramatic, i.e., up to ~?5% and ~?3.5% in the cold and warm subperiod, respectively. Present ozone level is still depleted over many popular resorts in southern Europe and northern Africa. For high latitude regions the trend overturning could be inferred in last decade (1995?2004) as the ozone depleted areas are not found there in 2004 in spite of substantial ozone depletion in the period 1985?1994.
Domaines
Océan, Atmosphère
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