Effects of a change of terrain height and roughness on a wind profile

Abstract

We have measured profiles of an onshore wind 200 m upwind and 200 m downwind from an abruptly rising shore using a remote-sensing Doppler lidar anemometer. Data were taken at heights between 4.7 and 66.5 m above sea level. Results show that the onshore velocity vector slopes upward 16.6 to 9.6°, the amount depending on the height of measurement, due to the combined effects of a 1.7-m high bluff shoreline and the frictionally decelerated flow over land. The profile 200 m inland has the expected deceleration at lower levels because of increased surface roughness and implies a velocity vector at 66.5 m height with an upward slope of approximately 18° (2.6 m s-1 upward component, 8.4 m s-1 vector magnitude), an acceleration to 0.3 m s-1 greater than the upwind value, or a combination of both effects. All three options are consistent with mass continuity. The experiment exhibits the usefulness and limitations of a backscatter Doppler lidar for boundary-layer profile measurements in a horizontally inhomogeneous environment.