Comments on the 'Universality of the Lagrangian velocity structure function constant (C-0) across different kinds of turbulence'

Recently Du (Boundary-Layer Meteorology 83, 207-219, 1997) estimated the va lue of the Lagrangian velocity structure constant, C-0, in the inertial sub range by comparing experimental diffusion data and simulation results obtai ned with the one-dimensional form of Thomson's model (J. Fluid Mech. 180, 5 29-556, 1987). Du reported that for several different flows (grid turbulenc e, a wind-tunnel boundary layer and the atmospheric surface layer under neu tral stratification) the value of C-0 is 3.0 +/- 0.5. Here, it is shown tha t optimal model agreement with experimental diffusion data for the wind-tun nel boundary layer is, in fact, obtained when C-0 = 5.0 +/- 0.5. It is also shown that accounting for the skewness of velocity statistics and finite R eynolds number effects does not significantly change this estimate for the value of C-0. It is suggested that one-dimensional Lagrangian stochastic mo dels are inconsistent with the supposed universality of C-0.