Further ozone decline during the northern hemisphere winter-spring 1994-1995 and the new record low ozone over Siberia
Bojkov R.D., V. E. Fioletov, D. Balis, C.S. Zerefos, T. Kadygrova, A. Shalamjansky
[περίληψη] During the second half of January 1995 through February and most of March very low ozone values again were observed in middle and high latitudes of the northern hemisphere. The ozone deficiencies fall 25% below the long-term mean over Siberia and Yakutia which lasted on the average for eight consecutive weeks! For a number of days in early February and in the second half of March, the deficiency exceeded 35-40% when ozone levels as low as 260-290 m-atm-cm were reported, while the long-term average is about 440-470 m-atm-cm. For a number of stations record low monthly ozone values were registered. Over eastern and central Europe in the same period the deficiency was 10-15% with few periods down to 20%. Over the western part of North America the deficiency was about 10-12% and the ozone levels were close to normal over the North Atlantic and Scandinavia. The monthly mean lower stratosphere temperatures over Siberia and eastern part of Europe were 10-12oC below the long-term normal for January and February falling down below -75oC to -80oC during the time of lowest ozone. Such temperatures is known to facilitate denitrification and chemical ozone destruction by anthropogenic chlorine and bromine compounds. Trajectory analysis at stratospheric levels show the air was coming over sunlit upper middle latitudes out of the center of the polar vortex whose core during most of the season was tilted towards Siberia. It is emphasized that the ozone deficiency is in concurrence also with the expected circulation induced ozone changes related to the westerly phase of the QBO and that the QBO was again one of the important factors as it was the case in the previous record low ozone observed during the winter-spring season of 1992-1993.
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