PRELIMINARY-RESULTS FROM POAM-II - STRATOSPHERIC OZONE AT HIGH NORTHERN LATITUDES

We present results from the first 18 months of measurements by the Polar Ozone and Aerosol Measurement experiment (FOAM TI) in the northern hemisphere. FOAM TI was launched on 25 September 1993, onboard the SPOT-3 satellite into a sun-synchronous polar orbit. The results presented here span a latitude range from about 55 degrees to 71 degrees, and an altitude range from about 18 to 35 km. Our results compare well with SAGE II data from 1986 to 1991. The observed variability in the zonally-averaged ozone retrievals is due to a convolution of the true seasonal variation in ozone with the seasonal variation in latitude of the FOAM Ii measurements. The seasonal variations in ozone at different altitudes reflect a transition between summer-time photochemical and dynamical control around 25 km. The longitudinal variation in ozone densities correlates well with the position of the measurement with respect to the polar vortex. Mixing ratios inside the vortex during the winters of 1993-1994 and 1994-1995 are indicative of enhanced descent within the vortex, as well as other dynamical processes and possibly chemical depletion.