UHF radar observation of strato-tropospheric transfers on the anticyclonic side of a jet streak

An observation by UHF ST radar of a subsidence pattern on the right side of the exit region of a jet streak is reported. The onset of the subsidence pattern occurred at 23:30 UTC on the 29 November 1991, when a downward motion was initiated above 14 km. The injections of stratospheric air in this region seem to have an intermittent nature; they occur during at least three intervals during the lifetime of the subsidence pattern. Comparison of these results with an ECMWF analysis suggests that it is an unfolding case. However, observation of turbulent intensities w' greater than 60 cm s–1 at the tropopause level also suggests the existence of a turbulent flux between the stratosphere and the troposphere. From the turbulence characteristics measured by the radar and the potential temperature profile obtained by radiosonde data, the eddy diffusivity at the tropopause level has been calculated. An eddy diffusion coefficient ranging between 5 and 7 m2 s–1 is found. From these values, and with the assumption of a climatological gradient of the volume mixing ratio of ozone in the lower stratosphere, it is possible to deduce a rough estimate of the amount of ozone injected from the stratosphere into the troposphere during this event. A rate of transfer of 1.5×1020 molecules of ozone per day and per square meter is found.