The summer stratospheric flow is analysed in three years of ECMWF analyses. By diagnosing the angular rotation, it is shown that the summer stratospheric flow is close to solid-body rotation for latitudes north of 30¿ with the rate of rotation increasing approximately linearly with height. This flow configuration is not in the radiatively determined state. The winds in thermal wind balance with the radiatively determined temperatures are unstable to barotropic/baroclinic instability. Small amplitude waves are diagnosed in the ECMWF analyses with periods of 5--10 days. These may drive the flow away from the radiatively determined state and lock the flow in the upper stratosphere into near solid-body rotation.