What is turbulence, what is fossil turbulence, and which ways do they
  cascade?
  Turbulence is defined as an eddy-like state of fluid motion where the
inertial-vortex forces of the eddies are larger than any other forces that tend
to damp the eddies out. By this definition, turbulence always cascades from
small scales (where the vorticity is created) to larger scales (where other
forces dominate and the turbulence fossilizes). Fossil turbulence is any
perturbation in a hydrophysical field produced by turbulence that persists
after the fluid is no longer turbulent at the scale of the perturbation. Fossil
turbulence patterns and fossil turbulence waves preserve and propagate
information about previous turbulence to larger and smaller length scales. Big
bang fossil turbulence patterns are identified in anisotropies of temperature
detected by space telescopes in the cosmic microwave background. Direct
numerical simulations of stratified shear flows and wakes show that turbulence
and fossil turbulence interactions are recognizable and persistent.
