AbstractThe unusual atmospheric behaviour observed at middle and high latitudes during the winter of 1976/77 is discussed in both synoptic and dynamical terms, using routine, objectively analysed data. During this period the growth of large amplitude, planetary‐scale waves in the troposphere resulted in a marked wave growth in the stratosphere. A qualitative discussion of the interaction between these waves and the zonal flow is followed by referring to the temporal evolution of the relevant terms in the zonally averaged momentum and heat equations. It is shown that the export of momentum from high latitudes by the waves was crucial in effecting a zonal wind reversal in both troposphere and stratosphere. The importance of this mechanism during the period of study indicates the need for a revision of the currently favoured dynamical model of the stratospheric sudden warmin