Oceanum Baltic Sea ECMWF Wave Forecast

February 2025

Dataset description

The Baltic Sea wave forecast dataset provides operational wave predictions across the entire Baltic Sea basin, including the Gulf of Bothnia, Gulf of Finland, Gulf of Riga, and the Danish Straits (Figure 1). The domain encompasses the coastal waters of Sweden, Finland, Estonia, Latvia, Lithuania, Poland, Germany, and Denmark. Wave forecasts are produced using the SWAN (Simulating WAves Nearshore) third-generation spectral wave model, with a 7-day forecast horizon updated every 12 hours (00, 12 UTC).

Wind forcing is provided by ECMWF IFS Open Data global atmospheric model. Sea ice concentration is prescribed from GFS to account for wave attenuation in ice-covered regions during winter months. Spectral boundary conditions are supplied by the Oceanum Western Europe ECMWF wave forecast. Bathymetry is derived from the GEBCO 2024 global bathymetric grid.

The modelling setup employs the ST6 source term parameterisations. Spectra are discretised into 36 directional bins and 43 frequency bins, covering a frequency range from 0.037 to 1.98 Hz with 10% logarithmic increments, extending to higher frequencies to capture the short-period wind waves characteristic of the enclosed Baltic Sea. The model features a regular grid with a 5 km (0.05 degree) resolution.

The dataset provides hourly forecast estimates for key ocean wave parameters (Table 2) including spectral quantities integrated over the full spectrum and for spectral partitions. Partitions are defined from an 8-second split (sea/swell) and from the Watershed method, which identifies one wind-forced partition and up to two swell partitions. Forecasts are archived for 30 days, and frequency-direction wave spectra are available at 1610 sites distributed across the domain. Nowcast datasets are also available, constructed by retaining the most recent data from each forecast cycle to provide a continuous near-real-time historical record.

Figure 1. Mean significant wave height from the Baltic Sea hindcast domain (used for forecast validation). The locations of 2D spectra hourly output are shown by the black dots.

Validation

The wave model physics and calibration have been validated against satellite altimeter observations for the corresponding hindcast domain. Validation results are available through the Oceanum Hindcast Satellite Validation App, which provides density scatter plots, quantile comparisons, and statistical metrics for the Baltic Sea region.

Data description

Table 1. Data description.

Linked Datamesh datasources

ECMWF-forced (12-hourly updates):

• Oceanum Baltic Sea ECMWF wave forecast parameters
• Oceanum Baltic Sea ECMWF wave forecast spectra

Nowcasts (continuous near-real-time archive):

• Oceanum Baltic Sea ECMWF wave nowcast parameters
• Oceanum Baltic Sea ECMWF wave nowcast spectra

Gridded output parameters

Integrated wave parameters are stored hourly over the domain at the native model resolution. Table 2 describes the gridded output parameters.

Table 2. Gridded output parameters.

Variable names link to the corresponding NERC Vocabulary Server standard name where available. All parameters are defined on the time, latitude and longitude coordinates.

Spectra output

Frequency-direction wave spectra are stored hourly at the spectra output sites within the domain. Table 3 describes the spectra output variables, using the exact variable names served by Datamesh.

Table 3. Spectra output variables.

Variable names link to the corresponding NERC Vocabulary Server standard name where available. Spectra are defined on the time, site, freq and dir coordinates; lon and lat are per-site data variables giving each site’s location.

www.oceanum.science