AbstractMeasurements have been made, under neutral conditions, of the turbulent wind structure on a 100m tower at the crest of a hill of heighth= 170m. A local velocity maximum, or ‘jet’, was observed at abouth/5, below which the ratio of increase in wind speed to the upwind value at the same height was 1.07, and almost independent of height near the surface.The r.m.s. turbulence components σw σv and σw were also approximately doubled near the surface, but whereas σu and σv both decreased with height, the surface increase in σw extended over the entire height of measurement. Reynolds stress was almost uniform above the ‘jet’, but increased sharply towards the surface, to 3–5 times the upwind value. Departures from neutrality affected the profile shape and the magnitude of turbulence fluctuations very markedly.Although the size of hill lay outside the range of validity of an analytical theory of Jackson and Hunt, their expressions for velocity and horizontal pressure gradient were in good agreement with the observations. Numerical theories by Frost, Harper and Fichtl and by Taylor, for hills of different shape, but similar slope to the experimental hill, also produced values of surface stress and velocity increase of the mag