Task: Instance Description Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes the instance 'bulk richardson number'?

A. The ratio of the effective permeability for a given flow phase to the intrinsic permeability of the porous medium (WMO, 1974). The ratio of the effective and specific permeabilities.
B. An approximation to the gradient Richardson number formed by approximating local gradients by finite difference across layers.
C. The ratio of the volume of water which the porous medium after being saturated, will yield by gravity to the volume of the porous medium.
D. The dimensionless ratio of the inertial force (∼U2/L) to the viscous force (∼ νU/L2) in the Navier–Stokes equations, where U is a characteristic velocity, L is a characteristic length, and ν is the kinematic viscosity of the fluid; thus, Re=ULv. the instance is of great importance in the theory of hydrodynamic stability and the origin of turbulence. The inertia force generates vortex stretching and nonlinear interactions and hence creates randomness. Turbulence occurs when the inertia term dominates the viscous term, that is, when the instance is large. For many engineering flows, turbulence occurs when Re > Rec, where the critical the instance is roughly Rec = 2100.

Answer: An approximation to the gradient Richardson number formed by approximating local gradients by finite difference across layers.