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Tolosa Documentation

Tolosa-sw Presentation

Tolosa-sw solves the shallow water equations (Saint-Venant) on unstructured meshes with original numerical schemes and CPU MPI parallelism. It is built on the Tolosa-lib library (included as a git submodule) and developed at the University of Toulouse (INSA, CNRS & SHOM).

It is deployed operationally at SHOM and Météo France for marine flooding warning, with Atlantic-scale forecasts (2.6 M cells) running in 5 minutes on 640 CPU cores.

Governing Equations

Section titled “Governing Equations”

where is the water depth, the bathymetry, the depth-averaged velocity, and:

ForcingSymbolFormulation
MeteorologicalAtmospheric pressure and wind stress
Bottom friction• Oceanic: , log-law
• Manning:
Coriolis

Boundary conditions: tidal forcing (internal SHOM tool) with optional inverse barometer correction .

See Equations and Modelisation for the full numerical formulation.

Supported Physics

Section titled “Supported Physics”
  • Bottom friction — three models, all supporting spatially variable coefficients loaded from external files:
    • Oceanic (friction_model=1): combined linear + quadratic drag; semi-implicit or exact implicit form
    • Oceanic with log-law (friction_model=2): quadratic coefficient recomputed from roughness length via log-law, clamped to
    • Manning/Strickler (friction_model=3): implicit scheme; RK2/RK3 corrector applied when needed
  • Coriolis — Crank-Nicolson semi-implicit discretization:
    • From latitude file: per cell from regional.grid-node.a,
    • Beta-plane: per cell
  • Open boundary conditions — ghost-cell approach with characteristic-based normal velocity: wall, neumann, q, ssh, tide, ssht, ssht/tide, h, ratcurve
  • SSH boundary forcing (ssht) — time-interpolated per boundary edge from ssht_edge_at_bc.a
  • Tidal body force — gravitational tidal potential computed analytically per constituent; applied to momentum at interval dt_tbf
  • Wind stress — [N/m²] from time-interpolated binary files
  • Atmospheric pressure — applied to momentum; optional inverse barometer correction at open boundaries

Operational Deployment

Section titled “Operational Deployment”

Tolosa-sw is used operationally at:

  • SHOM (French Hydrographic and Oceanographic Service): marine flooding warning for the French coast
  • Météo France: operational marine flooding warnings coupled with atmospheric (NWP) pressure forecasts

Performance benchmark on the Atlantic mesh (2.6 M cells):

  • 5-day forecast in 5 minutes on 640 CPU cores (Météo France supercomputer)
  • Tide prediction accuracy exceeds the previous HYCOM solver after stochastic data assimilation calibration over one year of integration

See HPC Performance for detailed benchmarks on larger meshes.

Next Steps

Section titled “Next Steps”