CLIMATOLOGY OF TROPOSPHERIC OZONE IN SOUTHERN EUROPE AND ITS RELATIONTO POTENTIAL VORTICITY

A climatology of the vertical ozone distribution in the troposphere is obtained by balloon-borne Brewer-Mast sondes at the Observatoire de H aute Provence (OHP), southern France (44-degrees-N, 6-degrees-E, 700 m above sea level), during the period 1984 to 1990. The tropospheric oz one seasonal variation is characterized by a large maximum in spring a nd summer. A comparison to other ozone sounding stations gives evidenc e for a meridional ozone gradient in the middle and upper troposphere in Western Europe, with larger ozone values at Uccle (51-degrees-N, 4- degrees-E) and Julich (50-degrees-N, 6-degrees-E) than at the OHP (44- degrees-N, 6-degrees-E). A statistical analysis of ozone concentration s together with potential vorticity, a tracer of stratospheric air mas ses, shows a partial but significant correlation between both variable s (r = 0.40, significance > 99.9%), implying a noticeable impact of st ratosphere-troposphere exchange on the ozone variability. Concerning t he spring/summer maximum of tropospheric ozone, it is shown to be caus ed both by ozone transfer from the stratosphere and by in situ photoch emical ozone production. A climatology of the ozone/potential vorticit y ratio is established for the OHP and its altitude and seasonal depen dence is given. Finally, it is shown that the interannual variability of potential vorticity can cause dynamically induced trends of the ozo ne concentrations, which have to be taken into account to determine ac curately the relative part due to human activity.