Turbulence Anisotropy in the Atmospheric Boundary Layer

The smallest scales of turbulence are isotropic, but the larger eddies, which contain more energy, are anisotropic. The scale of maximum turbulent kinetic energy (TKE) for shear dominated flows share similar anisotropy characteristics. When convection is present, the anisotropy properties of the maximum TKE scales are not as easy to classify.

Vertical variance is limited by the surface, resulting in smaller peak values which occur at shorter scales than for the horizontal variances. The interplay between the smaller scales for vertical variance and larger scales for horizontal flow and scalars such as temperature result in modified scales for the covariances. The scales of maximum temperature variance, heat flux, and momentum flux are typically larger than the isotropic scales and smaller than or equal to the maximum TKE scale.

Sonic anemometer data from the CASES99 main tower are used to examine the relationship between stability, elevation above the surface, and other meteorological conditions and the various peak scales and anisotropy characteristics.