INTERANNUAL VARIABILITY OF THE NORTH POLAR VORTEX IN THE LOWER STRATOSPHERE DURING THE UARS MISSION

Northern winters since the 1991 launch of UARS are compared to earlier years (1978-1991) with respect to the potential for formation of Pola r Stratospheric Clouds and for isolation of the north polar vortex. Da ily NMC temperature minima at 465 K late in the 1993-94 winter and aga in in December 1994 were the lowest values experienced at those times of year (since 1978). Northern PV gradients were unusually strong in 1 991-92 prior to late January and throughout the winter in both 1992-93 and 1994-95. Of all northern winters since 1978, 1994-95 with its ear ly extended cold spell and persistently strong PV gradients most resem bled the Antarctic winter lower stratosphere. Even so, temperatures we re never as low, nor was the polar vortex as large, as during a typica l southern winter. Judged by daily temperature minima and PV gradients at 465 K, meteorological conditions in the Arctic winter lower strato sphere during the UARS period were more conducive to vortex ozone loss by heterogeneous chemistry than in most previous winters since 1975-7 9.