Rd. Bojkov et Ve. Fioletov, CHANGES OF THE LOWER STRATOSPHERIC OZONE OVER EUROPE AND CANADA, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, 102(D1), 1997, pp. 1337-1347
Ozonesonde measurements from Europe and Canada for the period 1973-199
4 stratified to the height of the tropopause, were analyzed to estimat
e regional changes in stratospheric ozone. The calculations were perfo
rmed for 1-km layers from the actual tropopause up to 30 km and within
+/-4 km around the tropopause. The long-term changes in ozone partial
pressure are very similar for both regions, and ozone anomalies show
many common features. Negative deviations of 15-25 nbar (or 10-20%) ar
e clearly seen in 1976 (at 12-20 km), 1983 (at 17-22 km), 1985 and 198
8 (at 18-25 km), 1989 and 1990 (at 12-20 km), and 1992 and 1993 (at 12
-23 km). In January-April 1995, negative deviations of 15-25 nbar (at
12-23 km) were observed again over the two regions. Trend estimations
demonstrate that the strongest decline, in units of ozone partial pres
sure, takes place at 17-20 km over Europe in January-April and for Can
adian stations from March through June. For the period 1973-1994 the d
ecline over both regions is 10-13 nbar per decade (or 5-10% per decade
) and is similar to 1.5 times larger for the shorter time interval 197
9-1994. The estimation of trends as a function of altitude from the ac
tual tropopause level reduces the relative error in the 7 to 13-km lay
er by more than one third, which permits better understanding of the o
zone changes in these critical altitudes. Using stratified ozone data
around the height of the tropopause, the negative stratospheric winter
-spring trends became significant (10-15 nbar per decade or 12-17% her
decade) at only 1-2 km above the tropopause.