= Three-regime turbulent pair-separation model
For positive initial separation below the <Kolmogorov length scale>, a phenomenological pair-dispersion model has smooth-flow exponential stretching, inertial-range <Richardson pair dispersion>, and <diffusive large-scale pair dispersion> beyond the <integral scale of turbulence>. A positive <Lyapunov exponent> is needed for the first regime, scale locality and initial-memory loss for the second, and integrable relative-velocity <autocorrelation> for the third. The inertial-range crossing time is of order $L^{2/3}\epsilon^{-1/3}$, one outer <eddy turnover time>.
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