Diurnal Variation of Onshore Wind Speed Near a Coastline

Abstract

Surface wind data taken from 19 km offshore to 14 km inland during several days of onshore wind occurrence were reduced and analysed. The mean kinetic enemy per unit mass and its changes normal to the coastline were computed directly from the wind data. Analysis of these data shows two well defined regimes of diurnal variation in wind speed. The marine air has a nighttime speed maximum and a daytime minimum. As the air moves inland, the speed distribution becomes bimodal with the primary maximum occurring in the daytime and the secondary maximum at night. As expected Intuitively and predicted by theory, the speed changes most abruptly near the change in surface roughness (the coastline). Also as predicted by theory, complete dynamic equilibrium with the new lower boundary is not achieved until the air is ?5?12 km downwind from the coastline.