A direct numerical simulation (DNS) is performed on the turbulent Ekman boundary layer over two-dimensional wavy terrain. In the upper part of the Ekman boundary layer , a wind is driven by balance between the atmospheric pressure gradient and the Coriolis force. This is called the geostrophic wind. The hills are arranged perpendicularly to the direction of the geostrophic wind. The height of the hills is 1/8, 1/4, and 1/2 of the thickness of the Ekman boundary layer over the flat ground.

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... ent statistics such as the mean velocity profile and the velocity fluctuations are obtained. The recirculation vortex occurs in the valley between the hills. The flow in the direction parallel to the hill is dominant in the valley, while the one in the direction of the geostrophic wind is prevailing over the hilltop. The thickness of the Ekman boundary layer is significantly increased compared with the flow on the flat ground owing to the enhanced turbulence induced by the hilly terrain.