Airflow over an isolated hill

Perturbation theory is used to compute the vertical displacement of a uniform airstream passing over a solitary hill: first for a circular hill, then for a hill of oval section lying across the wind, obliquely to it and along it. The diagrams show contours of the vertical displacement at four different heights above the hill. It is significant that a small but steep‐sided oval hill produces almost as much displacement as a larger circular, less‐steep hill. When inclined obliquely to the airstream the pattern is very asymmetrical, the displacement being greater over the end of the hill that is farther down wind. A hill lying along the wind produces a very small effect.