STRATOSPHERIC-TROPOSPHERIC EXCHANGE AT POLAR LATITUDES IN SUMMER

Measurements of ozone number mixing ratio made in the mean troposphere, both within and above the boundary layer, at 60 degree N latitude over Canada in the summer of 1977, range from less than 20 to greater than 200 ppb. Isentropic analayses of the dynamic tropopause, on the basis of a potential vorticity threshold, show that the large-scale anomalies are related to traverses of a multiply folded tropopause; therefore, the large values of ozone are of stratospheric origin. Values less than 30 ppb are shown to be made directly in the boundary layer or in moist air which can be traced back to the boundary layer. The distinctions between the conventional and dynamic tropopause are discussed, and the use of potential vorticity as a stratospheric tracer is defended.