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.


Fig8.1.5-1: To view Wave Meteograms:

  1. On Forecast Charts and Data page, click on any Forecast Range.  A menu of available charts appears.
  2. Select Medium Range and Ocean Waves.  A selection of Wave Charts appears.
  3. Select any chart.
  4. Click on a desired location.  A meteogram for this location appears
  5. Click on the the chevron at the right of the title.  A dropdown menu appears.  Select 10 days Waves ENSgrams.  The desired Wavegram appears. 

Wavegrams are also available by clicking on "clickable" ecCharts at the desired location. 


Fig8.1.5-2: Alternative way to view Wave Meteograms (if desired location is known):

  1. On charts page, click ENS Meteograms.
  2. Select wave ENSgram from drop-down menu or display all ENSgrams by clicking on square icon.
  3. Select location by name or Lat/Long.


View directly an example of the wavegram site.


The divergence between the ECWAM ensemble members with respect to ocean waves is, therefore, due only to different wind forcing.  This can be attributable only to the coupled atmospheric ensemble members evolving in different ways, and indeed starting out from T+0 with (slightly) different fields of 10m winds (and other atmospheric parameters).   The ECWAM ensemble wavegram provides a probabilistic interpretation of the ECWAM ensemble for specific locations.  It displays the time evolution of the distribution of several marine parameters from the ECWAM ensemble at each forecast range by a box and whisker plot and information on wind and wave movement by a polar diagram (See Fig8.1.5-2).

Care should be taken when using ECWAM ensemble wave Meteograms for points very near to complicated coastlines, islands, or sea ice edges.  Main considerations are:


 

 Fig8.1.5-3: An example of a ECWAM ensemble wave Meteogram for the southern Denmark Strait (near 64N 35W) DT 00UTC 11 May 2017.  A strengthening NE wind is forecast over the location giving rise to amplified waves with increasing periods.  The mean wave direction indicates that on Saturday 13 May the waves become more directed towards the SSW with a higher proportion of ECWAM ensemble members showing very large waves (exceeding 9m significant wave height).  Note wind directions indicate where the wind blows from; wave directions indicate the direction the waves travel towards. The dotted red and continuous blue lines are the values of the control and CONTROL WAM forecasts respectively.


The significant wave height corresponds to the average wave height of the one third highest waves (H1/3).   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.

Significant wave height / Mean wave direction and height is also available on web free access charts.


Fig8.1.5-5: An example of Significant wave height probability greater than 4m.  DT Thursday 11 May, 00 UTC T+60, VT Saturday 13 May, 12 UTC. 

Significant wave height probability is also available on web free access charts.


Fig8.1.5-6: An example of wave energy flux magnitude (KW/m). DT Thursday 11 May, 00 UTC T+60, VT Saturday 13 May, 12UTC.  Colour thresholds are at 40KW/m intervals - lightest pink represents <40KW/m.

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:

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)