Relative Diffusion of Constant-Level Balloons in the Southern Hemisphere

Abstract

The TWERLE balloon tracers are analyzed for relative dispersion in the 150 mb level of the Southern Hemisphere and scales of 50?10 000 km. A two-particle time scale is introduced and is defined as the time integral of the relative-velocity correlation. This time scale is a function of both the initial relative distance between the pair of balloons and the Lagrangian integral length scale. Analysis of the relative-displacement data reveals an exponential growth region for short times after the release of the balloons and a t3 region for larger times (but smaller than the two-particle time scale). The exponential region can be considered as a manifestation of relative dispersion in an enstrophy cascade range while a t3 region indicates relative dispersion in a backward energy transfer region. Typical probability distribution functions of the relative displacement exhibit large kurtosis values. This can be regarded as a confirmation on the existence of a mixed local/nonlocal straining mechanism which affects both relative dispersion of balloons as well as kinetic energy transfer between the various scales. Relative velocities also are examined and, in general, are consistent with relative displacement results.