In 1996/1997 the polar vortex remained stable and stayed close to the north pole for the entire winter/spring period. Record low stratospheric temperatures at 50hPa were reached from the middle of March until the first week of April 1997, which were cold enough for type I PSCs to form (Coy et al., 1997). For instance, low total ozone columns (TOZ) of below 280 DU were observed inside the polar vortex on 2 April 1997 (see Fig. 2, middle).
Figure 2:
Top: Ozone height distribution along the GOME orbit Nr. 10197. White
contour lines indicate the various potential temperature levels.
Middle: Potential vorticity in units of 
m-3 at 
550K in
Northern Europe derived from ECMWF analysis. The latitude and
longitude scales for both maps are ranging from 40 to 80 deg N and
from 20 deg W to 70 deg E. The sub-satellite points of the GOME orbit
Nr. 10197 is indicated by the dashed line. Bottom: Total ozone field
derived from the GOME Level-2 Version 2.0 data in the same region as
shown in the middle plot. PV contour lines in units of 36-48 m-3 at 475K define
the polar vortex edge.
An altitude-latitude chart of ozone concentrations along part of a
selected GOME orbit, which started at mid-latitudes and crosses the
vortex boundary region into the polar vortex, is depicted in
Fig. 2. The polar vortex edge
runs across Northern Scandinavia (Fig. 2, middle and bottom). At about 65 deg
latitude ozone concentrations are strongly enhanced in the lower
stratosphere (11-21km altitude with a pronounced maximum at a height
of 18km, which may be caused by subsidence of ozone rich air masses as
it gets colder across the vortex edge (see also the small dip in the
lower 
-levels of the
potential temperatures). As one proceeds inside the polar vortex a
drop of ozone by roughly 60% at =475K is observed. A
significant reduction inside the polar vortex can be also seen in the
total ozone data as shown in the middle section of Fig. 2.
From the analysis of all fourteen daily GOME orbits a global 3D ozone distribution in the northern hemisphere can be derived. Fig. 3 shows the global ozone distribution in the lower (15-23km) and middle stratosphere (23-30km) on 2 April 1997. The layer column sizes are approximately defined by the full width at half maximum of the averaging kernels, which determines the vertical height resolution of the retrieved GOME profiles (Hoogen et al., 1998), and is about 8km in the lower stratosphere. A significant reduction of ozone levels of roughly 50% is observed in both altitude regions.
Figure:
Ozone column distribution in the altitude ranges 15-23 km (upper
panel) and 23-30 km (lower panel) on 2 April 1997.