Figure 2-4: Estimate of mean trend using all four measurement systems
(i.e., Umkehr, ozonesondes, SBUV, and SAGE I/II) at northern mid-latitudes
(heavy solid line). Combined uncertainties are also shown as 1s (light solid
lines) and 2s (dashed lines). Combined trends and uncertainties are extended
down to 10 km as shown by the light dotted lines. The results below 15 km
are a mixture of tropospheric and stratospheric trends, and the exact numbers
should be viewed with caution. Combined trends have not been extended lower
into the troposphere because the small sample of sonde stations have an additional
unquantified uncertainty concerning their representativeness of mean trends
(WMO, 1998).
