PSEUDO-WAVELET ANALYSIS OF TURBULENCE PATTERNS IN 3 VEGETATION LAYERS

Ramp patterns in scalar traces such as temperature are the signature o f coherent structures. A pseudo-wavelet analysis technique was develop ed in which ideal saw-tooth patterns of varying size were used as basi s functions and fitted to temperature and velocity data. Data recorded from three very different vegetation stands were examined in this stu dy. It was found that the most probable structure duration for the for est canopy was in the range 35-40 s, for the orchard canopy it was 20- 25 s and for the maize it was 15-20 s. When expressed in non-dimension al form, the structure duration probability distribution for the maize canopy was about a decade larger than for the forest canopy, with the orchard canopy intermediate. The mean eddy duration versus wind shear relation falls on a narrow band for all three canopies, indicating th at wind shear at the canopy top is the determining factor for the scal e of the coherent eddies. The inverse of duration and intermittency of coherent structures exhibits a tendency of independence from wind she ar at higher wind shear values. Coherent structures transport heat in a more efficient way than do smaller scale, less coherent motions. In ail the canopies, the heat flux fractions associated with coherent str uctures are at least 10% higher than the corresponding time fraction.