Anisotropy of the Fine Structure


  • J. C. Kaimal,

  • J. Borkowski,

  • S. Panchev,

  • D. T. Gjessing,

  • L. Hasse


Kolmogorov's theory postulates that the very small scales of motion in a turbulent fluid are isotropic. At the large end of these scales (inertial subrange) the spectral energy would be expected to fall off as the inline image power of wave number. Although it has been generally recognized that the inline image slope in the one-dimensional spectrum extends to wave numbers well below the limits predicted for the three-dimensional spectrum and cannot therefore be considered a sufficient condition for isotropy, it was assumed that local isotropy could be found if the measurements went far enough into the inline image region. Evidence presented at this meeting suggests that in the first few meters above the ground isotropy may never be reached even at scales small enough to be dominated by viscous dissipation. Above a height of approximately 20 meters, isotropy may be observed at wavelengths smaller than inline image the height above ground (i.e. a nondimensional frequency f > 10). In the free atmosphere, radio propagation experiments indicate that isotropy exists only at wavelengths of the order of 10 meters or less.