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

Abstract

The EOLE experiment with 480 constant–volume balloons distributed over the Southern Hemisphere at about the 200–nib level, has provided a unique set of trajectories of tagged particles in the general westerly circulation. All such data observed in the latitude belt 30 to 50S have been analyzed to estimate the mean square relative velocity (dD/dt)2 and mean diffusivity dD2/dt 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∼1000 km, and agrees well with the prediction of the two–dimensional turbulence model of atmospheric motions. The mean separation increases experientially with time up to 6 days, and more slowly like t½ later. An estimate of the gross austausch coefficient of the general circulation from these data is 1.6 × 102 m−2 set&−1. Abstract The EOLE experiment with 480 constant–volume balloons distributed over the Southern Hemisphere at about the 200–nib level, has provided a unique set of trajectories of tagged particles in the general westerly circulation. All such data observed in the latitude belt 30 to 50S have been analyzed to estimate the mean square relative velocity (dD/dt)2 and mean diffusivity dD2/dt 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∼1000 km, and agrees well with the prediction of the two–dimensional turbulence model of atmospheric motions. The mean separation increases experientially with time up to 6 days, and more slowly like t½ later. An estimate of the gross austausch coefficient of the general circulation from these data is 1.6 × 102 m−2 set&−1.