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ARCWAM (Arctic Ocean Wave Analysis and Forecast)

What this model is

ARCWAM is an operational regional wave analysis and forecast system for the Arctic Ocean and Nordic Seas, run by the Norwegian Meteorological Institute (MET Norway) and distributed through the Copernicus Marine Service.

It is a WAM-based spectral wave model covering the Arctic region north of approximately 53°N, with two distinguishing features among operational Arctic wave systems: explicit wave propagation under sea ice using a dimensional-analysis-based source function (Yu et al. 2022), and coupling to the ARC MFC physics and tidal systems for sea ice concentration, sea ice thickness, and surface currents. The system also includes multi-satellite altimetric data assimilation of significant wave height and wind, added in the November 2024 upgrade.

The official Copernicus Marine product identifier is ARCTIC_ANALYSIS_FORECAST_WAV_002_014. "ARCWAM" is not an official short name but reflects the product's role as the Arctic counterpart to BALWAM, MEDWAM, and IBIWAM in the Copernicus Marine wave portfolio. MET Norway also distributes three wave products directly through its own THREDDS server under CC BY 4.0 with no registration — WW3 4 km, MyWaveWAM3km, and MyWaveWAM800m. MyWaveWAM3km may be the same operational run as this product, distributed on its native rotated grid; see Relationship to other wave products below before treating the two as independent.

Who runs it

  • Production Unit: Arctic Monitoring and Forecasting Centre (ARC MFC), operated by MET Norway
  • Country: Norway
  • Role in Copernicus Marine: Production Unit for the ARC MFC wave product

What area it covers

  • Coverage: Arctic Ocean, Nordic Seas, and adjacent regions north of approximately 53°N
  • Domain bounds: 41.12°N – 89.99°N, 179.98°W – 179.98°E (global in longitude; north of 41.12°N in latitude)
  • Native grid: Rotated spherical grid at 3 km horizontal resolution
  • Delivered grid: Polar stereographic projection at 3 km resolution (straight vertical longitude from pole: -45°)
  • Grid dimensions: 2367 × 2467

Basic details

  • Model type: Regional deterministic wave model (coupled to ocean/ice, with data assimilation)
  • Core wave model: WAM Cycle 4.7 (code provided by Arno Behrens, Helmholtz-Zentrum Hereon; modified by MET Norway for wave propagation under sea ice)
  • Horizontal resolution: 3 km
  • Spectral resolution: 36 directions × 29 frequencies
  • Forecast length: Alternating cycles — 5 days (120 hours) from 00 UTC, 10 days (240 hours) from 12 UTC
  • Update frequency: 2× daily
  • Production cycles: 00 UTC and 12 UTC (bulletin times 06 UTC and 18 UTC respectively)
  • Target delivery time: 05:15 UTC (from 12 UTC cycle) and 16:15 UTC (from 00 UTC cycle)
  • Temporal output resolution: 1-hourly instantaneous
  • Analysis archive: Rolling archive from 2021-10-01 onward (Copernicus Marine product temporal extent)
  • Bathymetry: EMODnet Bathymetry and ETOPO1

Forcing and coupling

ARCWAM is forced by ECMWF atmospheric fields and coupled to the ARC MFC operational ocean/ice systems:

  • Atmospheric forcing: Six-hourly ECMWF 10 m winds (analysis and forecast)
  • Lateral boundary conditions: Six-hourly wave spectra from ECMWF
  • Sea ice concentration: Hourly from ARCTIC_ANALYSISFORECAST_PHY_002_001 (TOPAZ5)
  • Sea ice thickness: Hourly from ARCTIC_ANALYSISFORECAST_PHY_002_001 (TOPAZ5)
  • Surface currents: Hourly from ARCTIC_ANALYSISFORECAST_PHY_TIDE_002_015 (tidal-resolving Arctic ocean circulation system)

The coupling is off-line (one-way): ocean and ice fields influence wave propagation, but waves do not feed back into the physics run during the same cycle.

Wave propagation under sea ice

A distinctive feature of ARCWAM among operational wave systems is explicit representation of wave propagation in ice-infested waters. The system uses a new formulation of wave attenuation by sea ice based on Yu et al. (2022), introduced in the June 2023 upgrade. The sea ice source function is derived from a dimensional analysis scaled by sea ice thickness. Waves are allowed to propagate under the ice subject to frictional dissipation by the ice cover, rather than being suppressed entirely as in many global wave systems.

This is the state-of-the-art formulation described in the product's documentation as one of the refinements compared to the global wave product.

Data assimilation

ARCWAM uses Optimal Interpolation for significant wave height and 10 m wind observations from satellite altimetry. DA was added in the November 2024 upgrade (version 1.8), making ARCWAM a relatively recent addition to the set of Copernicus regional wave products with operational DA.

Assimilated observations (SWH and U10 wind)

  • Sentinel-3A
  • Sentinel-3B
  • Sentinel-6A
  • CryoSat-2
  • Jason-3
  • CFOSAT

Each 12-hourly forecast is preceded by a 12-hour analysis window in which assimilation is performed by OI against multi-satellite altimeter data.

What it provides

Hourly instantaneous fields of integrated wave parameters, partitioned swell fields, maximum crest/trough variables, and supporting ocean/ice context:

Total wave spectrum parameters

  • Spectral significant wave height (Hm0)
  • Wave periods: spectral moments (-1,0), (0,2), peak period (Tp)
  • Mean wave direction and principal direction at spectral peak
  • Stokes drift (U and V components)
  • Height of the highest crest (VMXL)
  • Maximum crest-to-trough wave height (VCMX)

Partitioned fields

  • Wind wave: height, period, direction
  • Primary swell: height, period, direction
  • Secondary swell: height, period, direction

Ocean and ice context fields (re-distributed from the physics forcing)

  • Sea ice concentration (SIC)
  • Sea ice thickness (SIT)
  • Surface current speed
  • Surface current direction

Data availability

Version history

November 2024 — Issue 1.8 (current)

  • Data assimilation added: Optimal Interpolation of SWH and U10 wind from Sentinel-3A/B, Sentinel-6A, CryoSat-2, Jason-3, and CFOSAT
  • Ocean currents product changed (now sourced from ARCTIC_ANALYSISFORECAST_PHY_TIDE_002_015)
  • Spectral frequency resolution updated

June 2023 — Issue 1.7

  • Two new LATERMAR output variables added (VMXL, VCMX — maximum crest height and maximum crest-to-trough height)
  • New formulation of wave attenuation by sea ice (Yu et al. 2022)

February 2022 — Issue 1.6

  • Global attribute changes

April 2021 — Issue 1.5

  • Correction of wave direction convention (from/to)

January 2021 — Issue 1.5

  • Inclusion of forecast currents and sea ice as forcing

September 2019 — Issue 1.4

  • Forecast frequency increased to twice daily
  • Horizontal resolution increased from 6.25 km to 3 km

November 2018 — Issue 1.3

  • Wave propagation under sea ice introduced
  • Current refraction added

February 2018 — Issue 1.2

  • Upgraded to wave V4 product

December 2016 — Issue 1.0

  • Initial version

Relationship to other wave products

MET Norway's operational wave portfolio

MET Norway publishes four operational wave products across two distribution channels:

  • ARCWAM (this entry) — WAM Cycle 4.7 at 3 km on a polar stereographic grid, Copernicus Marine, multi-satellite DA, ocean/ice coupling, 5/10-day alternating forecasts. Registration required.
  • MyWaveWAM3km — WAM Cycle 4.7.0 at ~3.34 km on a rotated grid, MET Norway THREDDS, current- and ice-forced, 120/240 h alternating × 2 daily. CC BY 4.0, no registration, but only a ~3-day rolling window and no archive.
  • WW3 4 km — WAVEWATCH III v6.07 at ~4.45 km, Nordic/North/Baltic Seas, 66 h × 4 daily, no documented DA. MET Norway THREDDS, CC BY 4.0, archive to 2021-07-02.
  • MyWaveWAM800m — WAM Cycle 4.7.0 at ~890 m, five Norwegian coastal domains, MEPS winds and NorKyst v3 currents. Nests inside WW3 4 km. CC BY 4.0, archive to 2023-03-30.

Unresolved: is MyWaveWAM3km the same run as this product? The two share operator, model core (WAM 4.7), resolution (3 km), spectral discretization (29 frequencies × 36 directions), cycling (2× daily), forecast lengths (120 h / 240 h alternating), 00/12 UTC production with 06/18 UTC bulletin times, ice and current coupling, and a northern bound of ~89.99°N. The most economical explanation is one operational run published on two grids — native rotated via MET Norway, polar stereographic via Copernicus Marine. Two things do not match: the southern bound (36.17°N vs 41.12°N here) and the delivered grid dimensions (2379 × 1995 vs 2367 × 2467), though the latter is uninformative across different projections.

This has not been confirmed with MET Norway. If the two are the same run, the November 2024 altimetric DA documented in this entry also applies to MyWaveWAM3km, whose entry currently records DA status as TBD. It would also mean the same data is available without registration through MET Norway's THREDDS. Until confirmed, both entries stand independently with this overlap flagged in each.

Copernicus Marine regional wave portfolio

ARCWAM sits alongside the other Copernicus Marine basin-scale regional wave products, each run by a different national institute:

  • BALWAM — Baltic Sea (FMI, Finland; WAM Cycle 4.7)
  • MEDWAM — Mediterranean Sea (HCMR, Greece; WAM Cycle 6)
  • IBIWAM — Iberian-Biscay-Irish waters (Nologin/CESGA, Spain; MFWAM)

Together these four systems form the core set of Copernicus Marine regional wave forecasts with multi-satellite data assimilation and coupling to regional physics/ice systems.

Relationship to the global MFWAM Copernicus product

ARCWAM receives its lateral boundary wave spectra from ECMWF (not from the Copernicus global MFWAM), which is a minor structural difference compared to IBIWAM and MEDWAM — both of which nest inside the global MFWAM product. This reflects ARC MFC's closer integration with ECMWF's operational atmospheric chain.

Notes

  • ARCWAM is one of the few operational wave systems with explicit representation of waves propagating under sea ice. This matters for Arctic applications where traditional suppression-based wave-ice treatments either overestimate wave damping in loose ice or fail to capture wave-ice feedback.
  • The product's temporal coverage ("Analysis from 2021-10-01") predates the November 2024 DA upgrade by about three years. Users running long retrospective studies should be aware that pre-November-2024 data in the rolling archive was produced without altimetric DA, while post-November-2024 data includes it.
  • The Copernicus Marine product documentation lists the product extent as "41.12°N to 89.99°N," while the PUM text refers to "north of 53°N" as the coverage area. The former is the actual grid extent; the latter reflects the practical forecast domain of interest. Users accessing data near the 41–53°N band should be aware that the southern edge of the grid includes some fill/boundary zone and should not be treated as equivalent-quality to core Arctic coverage.
  • The forecast-reference documentation notes a historical directional-convention issue (ARC-143) affecting pre-April-2021 data, where attribute definitions and actual directional values were inconsistent. The April 2021 v1.5 update corrected this. Users working with historical data from before that date should consult the Copernicus Marine User Notification Service.
  • For sea ice concentration and thickness, the values in ARCWAM files are re-distributed from the ARC MFC physics product and should match that product — users needing authoritative ice fields should cite the physics product rather than the wave product.

Official documentation