The spatiotemporal behavior of the ozone mixing ratio in the upper mesosphere/mesopause region under nearly polar night conditions is one of the phenomena not completely understood and reproduced by models thus far. We examine this issue using an advanced three-dimensional model of the dynamics and chemistry of the middle atmosphere (0--150 km) particularly designed to investigate the spatiotemporal structure of this phenomenon in the extended mesopause region. The most marked features of the modeling results are a pronounced ozone maximum around 72 km occurring close to the polar night terminator and a strong drop of the mixing ratio above ~80 km. These features were also found by means of ground-based microwave measurements in high latitude at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR, 69.29¿N, 16.03¿E) and even at the moderate latitude of Lindau (51.66¿N, 10.13¿E) during the night in the winter season but less marked there. They were absent at both stations during the daytime hours. The calculations suggest that the stronger enhanced ozone values occur in a latitudinal band of approximately 15¿ in the vicinity of the polar night terminator. During nighttime, enhanced values reach into midlatitudes. The effect is confined both to a height interval approximately between 66 and 76 km and to a certain latitudinal range which alters with season according to the change of the polar night terminator. We discuss the model results in terms of chemistry for nearly grazing incidence conditions of the solar insolation and in context with advective transport.