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Note: HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  With effect from Cy49r1, Ensemble Control Forecast (ex-HRES) output is equivalent to HRES output where shown in the diagrams.   At the time of the diagrams, HRES had resolution of 9km and ensemble members had a resolution of 18km.

Waves and wave meteograms

Wave meteograms (Wavegrams)

The ECWAM runs as an ensemble and produces a wide range of output in a similar manner to the ensemble atmospheric model.   The forecast data are based on the current resolution the ensemble.  All ensemble members use the unperturbed wave analysis as the initial condition.

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The significant wave height corresponds to the average wave height of the one third highest waves (H_1/3).   This means that there will be some waves of greater trough-to-crest height than indicated by the significant wave height.  Interference of wave trains, a shelving sea bed, or a contrary sea current are not represented in ECWAM and so may also induce much larger waves than shown.  The mean wave direction is the spectrally averaged propagation direction of the waves (weighted by amplitude). 

Example Wave Charts

 Fig8.1.5-4: An example of Significant wave height / Mean wave direction and height on ecCharts.  DT Thursday 11 May, 00 UTC T+60, VT Saturday 13 May, 12 UTC.  Note: Dark blue generally indicates areas in open water where waves are forecast to be very small (e.g. among the islands off western Scotland),  but the area of dark blue off the Greenland coast is in effect denoting sea ice.  The ice extent is modified during the forecast by information passed from NEMO to ECWAM.  This may affect the development of synoptic scale developments in the atmosphere with consequent influence over the forecast winds.

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The energy carried by swell and wind waves is important to aid assessment of potential damage to shorelines or fixed marine installations (e.g. oil rigs) and also as a guide to potential output of marine wave energy generation installations.   Charts of wave energy flux magnitude (the integral over all frequencies and directions of the product of the group speed and the two-dimensional energy wave spectrum) are available on ecCharts.

Long Swell Forecasts

Fig8.1.5-7:  Long swell forecasts.  ECWAM DT 00UTC 4 Jan 2014.  In the mid-Atlantic, significant wave height (left) is very high at about 20m.  This consists of swell at several periods.  Also shown is the wave energy in terms of swell height for:

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Note the wavelengths differ but are about 1km.  Wind waves have much shorter wavelengths. 

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)

• Read about techniques regarding satellite measurement of wave height.
• Read more on the wave model ECWAM.
• Read more on ocean waves at ECMWF and download lecture notes.
• Read more on ocean wave modelling
• Model output parameters and full list of available ECWAM output.
• Watch a comprehensive lecture on ocean wave forecasting at ECMWF or air-sea Interaction and earth system modelling.

(FUG Associated with Cy49r1)