Add a design document for Rayleigh damping - #496
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Rayleigh damping is a linear drag on momentum used during dynamic adjustment to remove the large-amplitude barotropic and inertia-gravity transients radiated by an initial condition that is not in dynamical balance. Omega has no such capability, which blocks generation of E3SM ocean initial conditions (Omega issue E3SM-Project#495). The design applies the damping implicitly, as an additional diagonal contribution to the existing implicit velocity vertical mixing solve in VelVertMixSetupOnEdge, so it is unconditionally stable for any product of the coefficient and the time step. It adds a single, spatially uniform coefficient in a new top-level RayleighDamping config group and introduces no new class or field. The depth-variable and bottom-only variants in MPAS-Ocean are deliberately not carried over. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Rayleigh damping is a linear drag on momentum used during dynamic adjustment to remove the large-amplitude barotropic and inertia-gravity transients radiated by an initial condition that is not in dynamical balance. Omega has no such capability, which blocks generation of E3SM ocean initial conditions (issue #495).
The design applies the damping implicitly, as an additional diagonal contribution to the existing implicit velocity vertical mixing solve in
VelVertMixSetupOnEdge, so it is unconditionally stable for any product of the coefficient and the time step. It adds a single, spatially uniform coefficient in a new top-levelRayleighDampingconfig group and introduces no new class or field. The depth-variable and bottom-only variants in MPAS-Ocean are deliberately not carried over.Checklist