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Wave Model Inputs and Outputs
Inputs and Outputs describe those parameters used to force the wave models, and the information produced as a result of the model runs.
Inputs
The Met Office wave models are forced by 10m wind fields derived from the Met Office Numerical Weather Prediction (NWP) model. This model provides data in a short range (past few hours) hindcast mode, and as a forecast with lead times out to 5 days ahead, over domains covering the Globe, North Atlantic and Europe, and UK.
The short range (to T+36) UK Waters wave model also incorporates time varying currents based upon the operational runs of the POL Surge Model. Fast flowing currents can have a significant effect on the wave field in specific geographical areas.
Outputs
Outputs from the Met Office second-generation wave model comprise:
- Forecast 2D frequency-direction wave spectra (16 directions, 13 frequencies) at predefined model grid cells
- Hindcast 1D frequency domain energy spectra plus mean directions (13 frequencies)
- Hindcast and Forecast integrated wave parameters as described below based upon the total wave spectrum, wind-sea part and swell part.
Integrated wave parameters provided are:
- Significant wave height (equivalent to average of the highest one-third of individual waves in the wave record)
- Peak energy period (for total wave spectrum only)
- Zero-upcrossing period ( this refers to the time interval between the surface elevation crossing the mean sea-level upward then over the crest, down into the trough and back to the mean sea level again. This measure of wave period will always give a value biased towards shorter period, as it is weighted with wave frequency squared)
- Principal direction from which waves are travelling (this is the average direction of the spectral frequency with the highest energy).
Wind-sea and swell are determined based upon a partitioning scheme that uses the wind field as its main determinant. Wind-sea waves are generated by local winds blowing over the surface of the ocean. Swell represents wind waves that have either traveled out of the area in which they were generated, or can no longer be sustained by the winds in the generating area. Using these definitions, the partitioning scheme defines a wave spectral cut-off frequency based upon wind-speed and cut-off direction based upon wind direction in order to derive wind-sea and swell parameters from the energy spectrum. It is possible however that for a given sea-state, swell may come from more than one direction and in these cases this simple partitioning scheme will be the source of some error. Further, when wind speed is highly variable, energy may rapidly switch between the wind-sea and swell parts.
Configuration output times
| Model Configuration | Max. Lead Time | Integrated Parameters Resolution | Spectral Data Resolution | Runs per day |
| Global | T+120 hours | 3-hourly | 6-hourly | 2 |
| European | T+36 hours | 3-hourly | 6-hourly | 2 |
| UK Waters | T+36 hours | Hourly | 3-hourly | 4 |
| Extended UK Waters | T+120 hours | 3-hourly | 6-hourly | 2 |
Archives
Data are output from the model and variously retained in commercially available fast-access hindcast archives and research based forecast model archives. Due to data handling constraints two-dimensional (frequency-direction) spectral data are output at specific model points only and are not archived. The hindcast archives are based upon one-dimensional (frequency) spectral data output for all model grid points. These data are used to construct integrated wave parameters including significant wave height, period and direction based on the total spectrum, wind-sea and swell components. The decomposition between swell and wind-sea is made using analyses based upon archived model values of wind speed and direction. Hindcast and forecast integrated parameters (e.g. significant wave height) are generated at model run-time for each model grid point and are retained in the research forecast model archive.
To obtain data or analysis services based on the wave model archives, please contact marine@metoffice.gov.uk
(Last Updated: 30-01-2008)