The effect of some meteorological factors on ozone variations in the northern hemisphere
Sassi, Ashour Salah
Ozone measurements using Dobson ozone spectrophotometer have been made in Canada since the late 1950s. These instruments were installed between 1957 and 1964 at five Canadian sites and replaced by the more advanced Brewer instruments in the mid- 1980s. Ozone measurements have also been made from satellites and in particular the daily global total ozone has been measured by the Total Ozone Mapping Spectrometer (TOMS) during the period October 1978 through May 1993. Since the 1970s the vertical profile of ozone concentration has also been measured with balloonsondes at several Canadian sites. Recent studies of ozone trends over Canada have shown negative trends in total ozone (WMO, 1994). In this thesis ozone trends in the troposphere and the lower to midstratosphere are examined using the three types of data sets. The purpose has been to investigate the ozone variation pattern in the northern hemisphere and to determine the possible effects of some meteorological factors on this variation during the period from January 1979 to December 1992. A statistical model for a trend analysis of the ozone time series has been used. The model included terms for seasonal variations in mean ozone and seasonal variations in ozone trends as well as the effect of some meteorological factors. An attempt to assess stratospheric temperature and ozone-temperature trends in the troposphere and lower and mid-stratosphere has also been made. It is concluded that while there is clear evidence for a negative trend in the total ozone column, the full coupling is masked by the seasonal variation.