Ozone depletion above Kiruna (67.9 ¿N, 21.1 ¿E), Sweden, was investigated using daily ozone and temperature measurements by ozonesondes between 1 February and 25 March 1997. Using UKMO Ertel's potential vorticity (EPV) and wind fields, three dynamically distinct regions were defined on a grid of isentropic surfaces viz.: the polar vortex boundary region characterized by steep EPV gradients, the area poleward of the boundary region (inside the polar vortex), and the area equatorward of the boundary region (outside the polar vortex). Due to dynamically induced displacements of the vortex, measurements were made in all three regions. By calculating the isentropic EPV at each measurement point and comparing it with the values defining the equatorward and poleward edges of the vortex boundary region, all ozone and temperature measurements could be binned according to their position relative to the vortex edge. Since the data outside the polar vortex were highly variable, mean ozone profiles and their standard deviations were calculated and compared only for the two other regions. To investigate whether differences between these mean profiles were indicative of ozone loss, the temporal evolution of ozone mixing ratios measured along several isentropic surfaces was examined, taking into the account the diabatic descent of airmasses. Finally, ozone loss rates were calculated for six potential temperature surfaces and loss rates of up to 0.63 ppm/month were found inside the Arctic vortex at surfaces descending from approximately 475 K (1 February) to 460 K (25 March). ¿ 1999 American Geophysical Union