How coherent are the vortices of two-dimensional turbulence?
  We use recent developments in the theory of finite-time dynamical systems to objectively locate the material boundaries of coherent vortices in two-dimensional Navier--Stokes turbulence. We show that these boundaries are optimal in the sense that any closed curve in their exterior will lose coherence under material advection. Through a detailed comparison, we find that other available Eulerian and Lagrangian techniques significantly underestimate the size of each coherent vortex. 
Mohammad Farazmand and George Haller
math.DS physics.flu-dyn physics.geo-ph