A case of strong warm-air advection over Lake Michigan was studied for changes in the atmospheric boundary-layer induced by interaction with the cold water surface. Wind and temperature data were taken at several levels in the boundary layer from a ship traveling approximately in the downwind direction. The instruments were attached to a tethered balloon.
In the case studied, the surface-based inversion that formed over the water rose to 140 m altitude after a minimum wind fetch of 50 km and remained at constant altitude for the rest of the fetch across the lake, a minimum of 150 km. A growing isothermal layer separated the inversion layer from an adiabatic mixed layer advected from upwind land areas. Substantial momentum decoupling between the inversion layer and the overlying layers was evident. A large wind shear in both speed and direction was found within the inversion layer below 100 m. Directional changes implied that the surface air traveled over a substantially longer fetch length than the air above the inversion. These data provided a good description of the evolving internal boundary-layer structure over the water surface.