text: For , advection is relatively unimportant, and so
  the magnetic field will tend to relax towards a purely diffusive state, determined by the boundary conditions rather than the flow.
  For , diffusion is relatively unimportant on the length scale L. Flux lines of the magnetic field are then advected with the fluid flow, until such time as gradients are concentrated into regions of short enough length scale that diffusion can balance advection.