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 si de of the exit region of a jet streak is reported, The onset of the su bsidence pattern occurred at 23:30 UTC on the 29 November 1991, when a downward motion was initiated above 14 km. The injections of stratosp heric air in this region seem to have an intermittent nature; they occ ur during at least three intervals during the lifetime of the subsiden ce pattern. Comparison of these results with an ECMWF analysis suggest s that it is an unfolding case. However, observation of turbulent inte nsities w' greater than 60 cm s(-1) at the tropopause level also sugge sts the existence of a turbulent flux between the stratosphere and the troposphere. From the turbulence characteristics measured by the rada r and the potential temperature profile obtained by radiosonde data, t he eddy diffusivity at the tropopause level has been calculated. An ed dy diffusion coefficient ranging between 5 and 7 m(2) s(-1) is found. From these values, and with the assumption of a climatological gradien t 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 f rom the stratosphere into the troposphere during this event. A rate of transfer of 1.5 x 10(20) molecules of ozone per day and per square me ter is found.