HNO3 AND PSC MEASUREMENTS FROM THE TRANSALL - SEQUESTERING OF HNO3 INTHE WINTER OF 1994 95/

In the winter of 1994/95 the TRANSALL research aircraft performed seve ral flights in the region of the Arctic vortex during the period of lo w stratospheric temperatures. The results of simultaneous measurements of HNO3 column amounts by the Michelson Interferometer for Passive At mospheric Sounding (MIPAS) and of aerosol backscatter profiles by the Ozone Lidar EXperiment (OLEX) are presented for two typical flight sce narios across the polar vortex boundary on December 17, 1994 and Janua ry 11/12, 1995. On December 17 and January 12, the column amounts of g aseous HNO3 decreased significantly in regions with low stratospheric temperatures. This decrease was correlated with the extent of the pola r stratospheric clouds. Depolarisation measurements showed that type I b PSCs were observed primarily, but equilibrium calculations for H2SO4 /HNO3/H2O aerosols seem to underestimate the observed HNO3 sequesterin g.