Abstract
Abstract Data from Deardorff's (1974) turbulence model are used in simulations of fluid particle and tetroon dispersion in the convective atmospheric boundary layer with −h/L ≫ 1, where h is the mixed-layer depth. It is found that the lateral spread σy(t) of tetroons about the mean wind direction is virtually identical to that of fluid particles for travel times t < ze/w*, where w* is the convective velocity scale and ze(<h) is the altitude of release, and also the equilibrium level of the tetroons. The rms lateral separation ly21/2; of tetroon and fluid particle pairs also are equal for travel times less than ze/w*. At larger travel times, both the σy and ly2 profiles of tetroons increase at slower rates than those of fluid particles. The simulations indicate that this is a consequence of the inability of tetroons to follow fluid particles through the turnaround zone z ≤ 0.2h where the kinetic energy of downward moving fluid is transformed into horizontal motion. Based on this finding it is shown that th...
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