Numerical simulation results are presented for the linear and nonlinear evolution of disturbances in a at Stokes layer. The response to a spatially localised impulsive forcing is investigated and it is found that the spatial-temporal development of the ow displays an intriguing family tree-like structure, which involves the birth of successive generations of distinct wavepacket components. It is shown that some features of this unexpected structure can be predicted using the results of a linear stability analysis based on Floquet theory
