A Numerical Investigation of Tetroon versus Fluid Particle Dispersion in the Convective Planetary Boundary Layer

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...