Addendum to "Coherent Lagrangian vortices: The black holes of   turbulence"
  In Haller and Beron-Vera (2013) we developed a variational principle for the detection of coherent Lagrangian vortex boundaries. The solutions of this variational principle turn out to be closed null-geodesics of the Lorentzian metric associated with a generalized Green-Lagrange strain tensor family. This metric interpretation implies a mathematical analogy between coherent Lagrangian vortex boundaries and photon spheres in general relativity. Here we give an improved discussion on this analogy. 
G. Haller and F. J. Beron-Vera
physics.ao-ph gr-qc math.DS