One fundamental quantity used in the measurement of oceanic
turbulence is 
, the rate of dissipation of kinetic energy
per unit mass. It tells us the rate at which energy is converted to heat
by friction. Another is 
, the rate of destruction of
temperature variance, i.e. the rate at which temperature gradients
are smoothed by molecular diffusion. N, the buoyancy frequency, provides
a time scale for many aspects of stratified flow. An important spatial
scale is the smallest scale on which velocity gradients can exist in
the face of viscous smoothing, the Kolmogorov scale, 
, where 
is the kinematic viscosity. Near
a boundary we speak of the friction velocity 
, defined
as 
, 
being the surface stress and 
the fluid's density. Also 
is von Karman's constant
(
).