Analysis and forecast outputs

Timing and duration of cycles

Presently, an ECCOFS 4D-Var analysis is conducted every day using observations aggregated for the proceeding 3 days, and this provides the basis of a new 5-day ocean forecast.

The control variables of the assimilation are the initial conditions (3 days prior to nominal "now") and time varying boundary conditions (over 3 days) on the coarse 6-km ECCOFS grid. As noted in the DA configuration description, the 6-km analysis increments are interpolated to the 3-km grid and the nonlinear model is re-run to complete the analysis step. The model state at the end of the analysis interval (notionally at day 0) become the initial conditions for a 5-day forecast on the 3-km grid. This forecast, decimated to the 6-km grid, becomes the background for the next analysis cycle the following day.

Modeling System Outputs

Browse products at Fathom Science

The web service https://eccofs.fathomscience.com presents a rolling display of the latest data assimilative analysis and 5-day forecast.

Outputs in AWS Registry of Open Data

Please note, we stress that the present pre-operational products are experimental and are the outcomes of a system still in active development. Nevertheless, we are making these results openly accessible to invite user feedback on the system skill and utility for applications.

Outputs from the data assimilative real-time system operated by the ECCOFS group are archived by NOAA's Open Data Dissemination (NODD) program in the AWS Registry of Open Data at https://registry.opendata.aws/noaa-nos-eccofs.

Output collections:

• HIS: Once daily snapshots (ROMS "History" files) at 00:00 UTC. All variables are on the ROMS native horizontal grid. For 3-D variables, outputs are given at all vertical s-levels. Horizontal velocities are in the ROMS curvilinear coordinate "xi,eta" directions.

  • Ocean state variables (sea level, depth-average and 3-D velocity, temperature and salinity)
  • Air-sea fluxes of heat (sensible, latent, long-wave and shortwave radiation, and their net sum) and moisture (evaporation, rain and effective net kinematic salt flux)
  • Surface and bottom stresses
  • Turbulent viscosity and diffusivity from the GLS turbulence closure

• AVG: Daily averages centered on 12:00 UTC. All variables are on the ROMS native Arakawa-C horizontal grid. For 3-D variables, outputs are given at all vertical s-levels.

  • All ocean state variables, air-sea fluxes, stresses and mixing coefficients as for the HIS files, plus
  • Derived quantities:
    • 3-D potential and relative vorticity
    • Ocean Heat Content (in kJ cm^-2) derived from the temperature anomaly with respect to the 26^oC isosurface (Leipper and Volgenau, 1972)
    • Mixed Layer Depth defined as the depth where density is 0.125 kg m^-3 greater than the density at z = -10 m, following Aristizábal Vargas et al. (2024)

• QCK: 3-hourly snapshots (ROMS "Quicksave" files) of 2-D variables on the ROMS native horizontal grid. Rather than in ROMS "xi,eta" coordinate directions, horizontal velocities are rotated to east-north Earth coordinates and reported on the same grid as tracers (temperature and salinity).

  • sea level, depth-averaged velocity (eastward, northward)
  • sea surface temperature, salinity and velocity (eastward, northward)
  • temperature, salinity and velocity (eastward, northward) at depths of 2 m, 50 m, and 100 m

• **STA: 1-hourly time series (ROMS "Stations" files) of sea level, temperature, salinity and 3-D velocity at selected locations corresponding to sustained or repeat observing sites operated by NDBC, CO-OPS, GLOSS, IOOS Regional Associations, and various NSF research programs.

File name schema:

• In the AVG and HIS collections, the date string encoded in the file name is the start date of the 3-day data assimilation window over which the inner loops of the 4D-Var Tangent Linear (TLM) and Adjoint (ADM) models are iterated. Filename suffices 0001, 0002 and 0003 denote the 3 days of assimilation analysis, whereas suffices 0004 through 0008 denote the 5 days of forecast initialized from the end state of the 3-day analysis cycle. Each file has one day of output. For example, on 15 June 2026, observations for the preceding 3 days June 12, 13 and 14, will be assimilated, and files for this cycle will be denoted eccofs_avg_20260612_000[1,2,3].nc. File eccofs_avg_20260612_0004.nc will be the forecast for June 15, the first day since analysis. Subsequent files eccofs_avg_20260612_000[5,6,7,8].nc will be the forecasts for June 16, 17, 18 and 19, respectively. In all cases, the ocean_time variable in each file can be interrogated to determine the correct time coordinate for the data in that file.

• In the QCK and STA collections there is a single file for each cycle that includes both the 3 days of analysis and 5 days of forecast.

Velocities

Note: ROMS velocities u, v, ubar and vbar are in the model native coordinates rotated with respect to earth coordinates (east, north) by the variable angle(lon,lat) that is stored in the output files. The components are also on a staggered Arakawa-C grid (i.e., the two components are not co-located). To convert to earth coordinates, u and v must be mapped to the rho (tracer) points grid where angle is defined, and the rotation applied. See the NOAA Tides and Currents FAQ on how to apply the rotation once u,v are mapped to the rho points grid. Some output files include variables with suffixes _eastward and _northward which are reported at the rho (tracer) coordinates with the rotation already applied.

Results

Skill assessment

Comparisons to other modeling systems