Coherent structures and incoherent turbulence.

Defines coherent structures in terms of spatially phase correlated vorticity, and discusses experimental defection of these structures. Notes an explanation of 'negative production' via coherent structures and their role in entrainment and production. For production the saddle is the most significant point. Flow visualization results indicate that the braid or saddle area is not a continuous two dimensional sheet, but consists of slender discrete vortices (ribs) aligned with the diverging separatrix the braid between the vortex roll consists of ribs which are stretched by the corotating rolls. The mechanism for production and entrainment is the same, vortex stretching. Location of mixing is studied. (C.J.U.)