The role of the stratospheric variability in the Arctic Oscillation (AO) is investigated by selecting 18 large month-to-month variation events. It is shown that although tropospheric features are very similar, the vertical structure of the AO differs considerably depending on whether it is initiated by a downward propagation of zonal-mean zonal wind anomalies from the stratosphere (type S) or it is produced within the troposphere (type T). Type S events preferentially occur during February and March, while type T events are seen during November and December. The results of the analysis suggest that diverse aspects of the AO-related variability can more easily be understood as coupling and uncoupling of stratospheric and tropospheric modes of variability. ¿ 2000 American Geophysical Union