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ACCESS‑ISSM (ALPHA RELEASE)

ACCESS‑ISSM model

The ACCESS Ice Sheet–Shelf System Model (ACCESS‑ISSM) is a global ice‑sheet and ice‑shelf model based on the ISSM framework. It supports standalone ice dynamics and optional coupling to ocean and atmospheric forcings. This suite is in alpha: we welcome feedback and contributions via our GitHub repository.

Configurations & Resolutions

ACCESS‑ISSM alpha provides the MISMIP suite which reproduces the Marine Ice‑Sheet Model Intercomparison Project benchmark in ACCESS‑ISSM. It is intended for code regression tests, parameter experiments and numerical‑scheme development

1.1 Domain & Physics

  • Geometry: 800 km × 80 km Cartesian slab; flat bed at –1500 m; ocean at the downstream end.
  • Boundary conditions: Marine ice sheet with grounding line migration; zero inflow at upstream wall; periodic lateral boundaries (y‑direction).
  • Flow law: Glen’s (n = 3) unless stated otherwise.
  • Thermodynamics: Isothermal (268 K) in the benchmark script.
  • Available solvers:
  • SSA: default transient spin‑up.
  • HO / FS: optional higher‑order checks (after 3‑D extrusion).

1.2 Mesh Options

Nominal Δx (m) Label in driver Typical vertex count Use‑case
2000 2km_viscous or 2km_coulomb  ≈ 160 × 16 k Fast test runs
1000 1km_viscous or 1km_coulomb  ≈ 320 × 32 k Standard benchmark
500 500m_viscous or 500m_coulomb  ≈ 640 × 64 k Convergence studies
200 200m_viscous or 200m_coulomb  ≈ 1600 × 160 k High‑resolution reference

Basal friction law options:

  • Viscous (power‑law, (m = 3)): *_viscous labels.
  • Coulomb (plastic till): *_coulomb labels, using (\tau_b = C_0 + C_c |\sigma_n|).

1.3 Workflow Steps

The driver script (see mismip_driver.py) is orchestrated by an organizer object. Key stages:

  1. Mesh_generation → BAMG generates unstructured triangular mesh at chosen resolution.
  2. Parameterization → masks & initial geometry via Mismip.py.
  3. Transient_Steadystate → 200 kyr relaxation with SSA.
  4. (optional) Transient_extrude → extrude to 3‑D and switch to HO.
  5. GlenSSA / GlenMOLHO / GlenHO → Glen‐law transient experiments.
  6. ESTARSSA / ESTARHO → dual‐E (star) rheology experiments.
  7. analyse → automatic velocity‑field comparison and summary plots.

To run only the first comparison plot on Gadi, adapt the example job script below (full listing in docs):

qsub run_mismip_first.sh   # runs steps 1–7 and stops

Warning
ACCESS‑ISSM is in alpha. Expect API changes and incomplete documentation. Use for testing and development only.

More details, examples and forcing files are available on the ACCESS‑ISSM GitHub.

Run ACCESS‑ISSM