Spatially Resolved Near Surface Motions in the Atmospheric Boundary Layer

PIV data were collected from the SLTEST site in Utah. The site was chosen because conditions produce a high Reynolds number boundary layer (Rq = O(106)) over a flat surface. Time averaged results indicate that the data are an accurate representation of a rough wall laboratory boundary layer with zero pressure gradient. Instantaneous realizations of the velocity field show an inclined shear layer in approximately 40% of the images at a mean angle of 19o. The shear layer separates a region of relatively uniform high momentum from a region of relatively uniform low momentum. This shear layer typically exhibits a set of vortex cores identified by circular streamlines in a convected reference frame. Conditionally averaging the velocity field based on high swirl strength yields inclined regions of low momentum and inclined streamlines. These results supplement the work of previous authors who have found these features in low Reynolds number flows.