Neutral Equivalent Surface Stress

In laboratory turbulent flows, it has been observed that the eigen axes of the Reynolds stress tensor are oriented 17 deg from the streamwise coordinate system. Atmospheric flows are more complex, even over relatively flat terrain under thermally neutral conditions. The orientation of the eigen axes with respect to streamwise coordinates is examined using CASES99 main tower data. The relationship is then used as the basis for a neutral equivalent momentum transport. Although more complex than the standard methods to calculate surface stress, this new method can be calculated in complex environments, such as urban canyons, where the influence of multiple wall normals makes conventional calculations of momentum transport problematic.