VerCOR

Versatile Earth system COupleR (VerCOR) connects atmosphere, ocean, sea-ice, land, and forcing-data components on a shared clock. It helps Earth-system researchers compose models, exchange fields between grids, and collect diagnostics and output.

VerCOR is built on JAX. Output-free JAX workflows remain differentiable end to end, supporting sensitivity analysis, automatic differentiation, and gradient-based experiments.

Stable release: Version 0.4.5 is the current release. VerCOR 0.3 applications should follow the Migration guide.

Key capabilities

• Combine JAX-native and host-side models in one coupled simulation.
• Exchange scalar and vector fields between rectilinear grids.
• Use bilinear or conservative regridding.
• Run Gregorian, no-leap, or 360-day calendars.
• Use bundled slab atmosphere, ocean, land, and sea-ice components.
• Connect optional JCM, Veros, and CAMulator models.
• Supply static or time-dependent forcing data.
• Preserve immutable state across JAX transformations.
• Enable period averages, final fields, and snapshots when requested.

Requirements and installation

VerCOR supports Python 3.12 and 3.13 and requires a JAX installation supported by your platform.

Install the core package:

python -m pip install "vercor==0.4.5"

Install an optional extra before using a bundled JCM or Veros setup:

python -m pip install "vercor[jcm]"
python -m pip install "vercor[veros]"

CAMulator additionally requires NCAR's MILES-CREDIT. A compatible CREDIT release has not yet been confirmed or pinned.

Version 0.4.5 is the current release. Upgrade an older installation for the published stable API:

python -m pip install --upgrade "vercor==0.4.5"

Quick start

This dependency-light example runs a slab ocean for two one-hour steps:

from datetime import datetime

import jax.numpy as jnp

from vercor import Clock, Coupler, RectilinearGrid
from vercor.setups import make_slab_ocean


grid = RectilinearGrid.uniform(
    "quickstart",
    nlon=2,
    nlat=2,
    longitude=(0.0, 360.0),
    latitude=(-90.0, 90.0),
)
clock = Clock(datetime(2000, 1, 1), dt_seconds=3600.0, steps=2)
ocean = make_slab_ocean(grid)
coupler = Coupler(clock, components=(ocean,), run_order=(ocean.name,))

final_state = coupler.run()
sea_surface_temperature = final_state.component(ocean.name).field(
    "sea_surface_temperature"
)

assert sea_surface_temperature.shape == grid.shape
assert bool(jnp.all(jnp.isfinite(sea_surface_temperature)))

Setup gallery

VerCOR packages runnable setup scripts with its distribution. List the available templates, copy one into a user-editable directory, then run that local copy:

vercor show-setups
vercor copy-setup run_jcm_with_veros \
  --to ~/vercor-setups/run_jcm_with_veros
vercor run \
  --loglevel info \
  --float-type float64 \
  ~/vercor-setups/run_jcm_with_veros/run_jcm_with_veros.py

vercor --version reports the installed distribution version. VERCOR_SETUP_DIR may add external templates as an os.pathsep-separated list of direct directories. Every template name must be unique across the packaged gallery and those directories; duplicates are errors. copy-setup --to creates missing parent directories or reuses an existing directory, but never overwrites an existing setup file.

An external template must define exactly run_setup(*, loglevel, float_type). vercor run passes lowercase-only loglevel choices (trace, debug, info, warning, or error) and float_type choices (float64 or float32); their defaults are info and float64. The function returns None for success or an integer process status.

Documentation

Read the canonical documentation at https://vercor.readthedocs.io/:

• Researcher guide
• Developer guide
• Python API
• Migration guide
• Plugin authoring

Repository resources:

• Changelog
• License