Forcing

This page describes design and implementation details for forcing-related pathways in Omega, currently this includes:

• Wind forcing

• Surface tracer restoring

Wind forcing design

Wind forcing data flow

1. External fields provide:

   • WindStressZonal

   • WindStressMeridional

2. Auxiliary-state compute builds NormalStressEdge from those fields.

3. Tendency term applies wind-stress forcing to edge-normal velocity tendency.

Wind forcing key classes/components

• WindForcingAuxVars

  • Stores wind-stress cell fields and computed NormalStressEdge

  • Applies configured interpolation choice (InterpType)

• AuxiliaryState::computeMomAux

  • Calls WindForcingAuxVars::computeVarsOnEdge

• WindForcingOnEdge tendency term

  • Adds contribution proportional to normal stress and inverse layer thickness in the surface layer

Wind forcing config coupling

• Omega.WindStress.InterpType

  • mapped to InterpCellToEdgeOption

• Omega.Tendencies.WindForcingTendencyEnable

  • gates execution of wind forcing tendency kernel

Surface tracer restoring design

Surface tracer restoring data flow

1. External fields provide target values: TracersMonthlySurfClimoCell (values and units should match the state variables)

2. Auxiliary-state compute forms restoring differences: SurfTracerRestoringDiffsCell = target - tracer_surface

3. Tendency term applies restoring only at surface layer and only for tracers selected from SurfaceRestoring.TracersToRestore.

Surface tracer restoring key classes/components

• SurfTracerRestAuxVars

  • Inputs: TracersMonthlySurfClimoCell, tracer state array

  • Output: SurfTracerRestoringDiffsCell

  • Uses MinLayerCell to select surface layer index

• SurfaceTracerRestoringOnCell tendency term

  • Applies PistonVelocity * SurfTracerRestoringDiffsCell at surface

• Tendencies

  • Parses SurfaceRestoring.TracersToRestore and resolves tracer indices

  • Builds TracerIdsToRestore and NTracersToRestore

  • Applies tracer-selection logic at call site in computeTracerTendenciesOnly

  • Aborts if restoring is enabled but no tracer IDs are available

Surface tracer restoring config coupling

• Omega.SurfaceRestoring.PistonVelocity

  • tendency scaling

• Omega.SurfaceRestoring.TracersToRestore

  • tracer-level enable list used to build TracerIdsToRestore

• Omega.Tendencies.SurfaceTracerRestoringEnable

  • gates restoring tendency execution

Notes

• If a tracer is not listed in TracersToRestore, no restoring tendency is applied to that tracer.

• If restoring is enabled but no tracer IDs are available at tendency compute-time, Omega aborts with an error.

• It is assumed that the incoming TracersMonthlySurfClimoCell fields (values and units) match the Omega state variables (i.e. conservative temperature and absolute salinity for Teos-10). If not, a pre-processing conversion should be implemented.

• Surface tracer restoring is active everywhere if enabled. A flag to turn it off under sea ice will need to be added in later development if this feature is desired.

• Unlike MPAS-Ocean, a MaxDiff clamping is not applied here. This check should instead be implemented in Ocean Validate when that is available.

• A global scaling to ensure zero-sum has not been implemented for the surface tracer restoring, but should be added in later development.

• At this stage, there is no temporal interpolation applied to the restoring targets, the raw TracersMonthlySurfClimoCell snapshot is used.