Evidence for a k^-5/3 spectrum from the EOLE Lagrangian balloons in the low stratosphere

The EOLE experiment is revisited to study turbulent processes in the lower stratosphere circulation from a Lagrangian viewpoint and to resolve a discrepancy on the slope of the atmospheric energy spectrum between the work of Morel and Larchevêque and recent studies using aircraft data. Relative dispersion of balloon pairs is studied by calculating the finite-scale Lyapunov exponent, ah exit-time-based technique that is particularly efficient in cases in which processes with different spatial scales are interfering. The main goal is to reconciliate the EOLE dataset with recent studies supporting a k^-5/3 energy spectrum in the 100-1000-km range. The results also show exponential separation at smaller scales, with a characteristic time of order 1 day, and agree with the standard diffusion of about 10 ⁷ m² s^-1 at large scales. A remaining question is the origin of a k^-5/3 spectrum in the mesoscale range between 100 and 1000 km.