The vertical structure of the coastal zone boundary layer is examined from tower data collected during the Risoe Air Sea Experiment off the coast of Denmark and from LongEZ aircraft data collected in the Shoaling97 Experiment off the coast of North Carolina. In the latter experiment, the vertical structure of the boundary layer was examined in terms of aircraft flights at different levels, aircraft soundings and SODAR profiles. The analysis of the Danish data emphasizes formation of flow of warm air over cooler water leading to stable internal boundary layers while the North Carolina data contains a variety of cases with substantial change of wind speed and direction at the boundary layer top.
Atmospheric boundary layers in the coastal zone assume a variety of unique forms due partly to land sea contrasts and resulting mesoscale circulations and internal boundary layers. Locally driven mesoscale flows in the boundary layer lead to substantial shear at the top of the boundary layer, above which, synoptic scale flow dominates. In some cases, the stress at the top of the boundary layer may be as large, or larger, than the surface stress. Large stress at the top of the coastal zone boundary layer may also be driven by advection of turbulence from land which over-rides internal boundary layers in the coastal zone.