Dispersion of tracers in the atmosphere and ocean: Survey and comparison of experimental data

Experimental data on the dispersion of clouds of inert tracers in the atmosphere are presented as a function of time after injection for a variety of altitudes from the planetary boundary layer to the turbopause, and for times ranging from minutes to months, extending the compilation of Hage (1964). The results on horizontal dispersion are compared with similar data for the upper ocean (depths less than 60 m) compiled by Okubo (1971). All the data show a strong scale dependence of the effective eddy diffusivity. Within the wide range of variability of the data in the lower atmosphere (0–30 km) there is no explicit altitude dependence of the effective mean eddy diffusivity at a given length scale σn, and all the data (for lower atmosphere, upper atmosphere, and ocean) show a scale-dependent horizontal eddy diffusivity with a similar dependence on cloud size σn. Absolute differences between atmospheric and oceanic diffusivities are related to a variation in mean values of the turbulent dissipation rate e, and comparison is made with the classical analysis of Richardson (1926).