TRANSITIONAL OR OUTER FRICTIONAL TURBULENCE LAYER Here frictional turbulence, generated in the layer below, still domin ates vertical diffusion, but it dies out gradually until, at the top of the layer, both turbulence and diurnal temperature changes disappear. Both layers may be dusty, and the top of the transitional zone is sometimes visible as a distinct dust horizon at 500-1000 metres, marking the upper limit to which spores are raised by frictional turbulence (though much greater heights may be attained by convection).
In dynamical meteorology this zone is defined as the region where the wind structure is determined partly by surface friction and partly by the Earth's rotation.