Relative Dispersion of Constant–Level Balloons in the 200–mb General Circulation

The EOLE experiment with 480 constant-volume balloons distributed over the Southern Hemisphere at about the 200-mb level, has provided a unique set of trajectories of tagged particles in the general westerly circulation. All such data observed in the latitude belt from 30 to 50 S have been analyzed to estimate the mean square relative velocity and mean diffusivity of balloon pairs separated by the distance D. It is found that the eddy dispersion process is homogeneous, isotropic and stationary up to scales D approximately equal to 1000 km, and agrees well with the prediction of the two-dimensional turbulence model of atmospheric motions. The mean separation increases exponentially with time up to six days, and more slowly like the square root of t later. An estimate of the gross austausch coefficient of the general circulation from these data is 1,600,00 sq m/sec.