A three-dimensional model using winds and temperatures from the Goddard Earth Observing System Data Assimilation System is used to simulate ozone evolution in the winter high-latitude northern lower stratosphere. The simulation results are compared with ozone observations from three platforms: the differential absorption lidar (DIAL), the Microwave Limb Sounder (MLS), and the Polar Ozone and Aerosol Measurement (POAM II). Time series for the different data sets are consistent with each other, and diverge from model time series during December and January. The model ozone in December and January is much less sensitive to the model photochemistry than to the model vertical transport. Simulations with different initial conditions for ozone demonstrate sensitivity to the model ozone profile shape. The modeled ozone throughout December and January most closely resembles observed ozone when the vertical profiles between 12 and 20 km within the polar vortex closely match December DIAL observations. We make a quantitative estimate of the uncertainty in the vertical advection using diabatic trajectory calculations. The net transport uncertainty is significant and should be accounted for when comparing observations with model ozone. The observed and modeled ozone time series during December and January are not inconsistent when these transport uncertainties are taken into account. ¿ 2001 American Geophysical Union