Analysis of the eect of the coastal discontinuity on near-surface ̄ow

Conditional sampling is used herein to examine the e€ect of fetch, stability, and surface roughness changes on wind speeds in the coastal zone. Using data from an o€shore wind farm it is shown that at a distance of 1.2±1.7 km from the coast, up to a height of 20 m above the surface, di€erences in wind speed distributions from onshore and o€shore masts are statistically signi®cant for ̄ow moving o€shore under all stability conditions. In contrast, di€erences between the distribution of wind speeds at 38 and 48 m at masts located at the coast and in the coastal zone are not signi®cant for ̄ow moving o€shore, indicating that ̄ow at these heights is not fully adjusted to the change in surface roughness (land to sea). These ®ndings are in accordance with calculations of the internal boundary layer (IBL) height which indicate that the IBL would frequently be below the two upper measurement heights at 1.2±1.6 km from the coast. The analyses presented here indicate that the wind speed distribution at a potential o€shore wind farm site is not solely dependent on fetch (distance from the coast) but also depends on the stability climate.