  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 vorticity is created to larger scales where 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 energy and information about previous turbulence.
Ignorance of fossil turbulence properties can be dangerous. Examples include
the Osama bin Laden helicopter crash and the Air France 447 Airbus crash, both
unfairly blamed on the pilots. Observations support the proposed definitions,
and suggest even direct numerical simulations of turbulence require caution.
