The influence of thermal stability and angle of incidence on the acceleration of wind up a slope

Observations show that the increase in speed as wind blows over a low hill of length L varies with stability in a way which supports the role of the Jackson and Hunt (1975) reference velocity uL in determining the surface pressure perturbation. Speed-up tends to become constant with increasing stability, due to the limiting effect of the shallow nocturnal boundary layer. The magnitude of speed-up at neutral stability is well predicted when the hill shape factor is properly specified. There are significant effects on speed-up due to surface roughness and angle of incidence to the ridge.