Abstract
Abstract
Abstract
With the Match technique, which is based on the coordinated release of
ozonesondes from a network of sounding stations in the Northern
Hemisphere in order to obtain a large number of double probed air
parcels, the chemical ozone loss inside the stratospheric polar
vortex was quantified during the winters 1996/97, 1997/98, and
1998/99.
Large interannual differences regarding the amount of chemical
ozone loss were detected. In winter 1996/97, the coldest winter
examined here, ozone loss was detected in February and March,
with maximum vortex averaged loss rates around 40 ppbv/day.
Overall, the ozone loss was lower than in the two preceding years,
because only the inner part of the polar vortex was affected by major
ozone loss. Despite this, the total ozone column densities that where
observed in spring 1997 were lower compared to both years before,
which indicates a large dynamical contribution. In winter 1997/98,
temperatures were higher than in preceding years, and only slight
ozone loss was detected, which was probably connected to lee wave
formation at the edge of the polar vortex. In winter 1998/99, the
warmest winter examined with Match so far, no chemical ozone loss was
detected. These results demonstrate clearly that, given the present
chlorine loading, the amount of ozone destruction in the Arctic
stratosphere is determined by the temperature distribution.
In this work, the dependence of the ozone loss rates on the
temperature histories of the air parcels was analysed for the
first time. Using all Match data that were obtained inside the
polar vortex in an isentropic level of 475 K during the years
1995-2000, it was shown that chemical ozone loss in February occurred
solely within those air parcels that experienced temperatures below
193-195 K either between the two soundings or up to ten days before
the first sounding. According to the present understanding of the
seasonal ozone loss in polar regions, stratospheric chlorine is
activated below certain threshold temperatures, which then initiates
ozone destruction. The results obtained in this work give experimental
evidence for the existence of such a threshold temperature being of
significance for the ozone destruction. For the altitude under
consideration, the threshold temperature determined in this work
agrees with the threshold temperature for chlorine activation that was
observed by others.
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