Wave Validation Further Info

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Operationally generated graphics of the wave fields (no spectra or source terms) are available from Model Analyses and Guidance.

Bulletin files are available from the Production FTP/HTTPS server. Look for gfs.YYYYMMDD/CC/wave/station/bulls.tCCz/gfswave.stationID.bull

Observed wave height distributions for in particular the NW Atlantic Ocean show a large impact of the fact that the data is binned with bin sizes close to the resolution of the archived wave heights (see Tolman 1998b,d)
In general the wave model performs poorly when compared to the Japanese buoys , in particular in terms of scatter indices. There are several potential explanations for this behavior: (i) The corresponding wind fields include large errors (see discussion of winds above). (ii) Low mean wave height in this area making the scatter index sensitive. (iii) A significant part of the error appears to be due to systematic positive biases, which might be related to the unresolved Ryukyu Islands (see discussion of the validation with satellite data below). (iv).The diffiulty of wind models in dealing with Typhoons
The wave model shows excellent behavior when compared to the buoys around Hawaii , with small rms errors and scatter indices around 15% for the hindcast. In the northern hemisphere winter, however, a large positive bias occurs, and the scatter index grows to about 25%. This is at least partially due to the fact that all buoys except for 51001 then are to some extend sheltered by the islands from swell propagating form the north. Because the islands are not resolved by the wave model, swell dissipation at the shores of the islands is not modelled, and a positive bias will therefore occur south of the islands. This can be observed in the validation with altimeter data below. In contrast, the wave model shows much better result for buoy 51001, which is not sheltered behind the islands. For instance, scatter indices for buoy 51001 for the hindcast from January and February 1998 are 16%, and 20%, respectively. Wave conditions in this area are mostly dominated by swell fields, which are less sensitive to forecast errors than wind seas. Error growth with forecast time therefore is smaller than forthecompositebuoydataset
For the Gulf of Mexico , the wave model shows small biases and rms errors. Due to the generally low wave heights, scatter indices are high in particular in the northern hemisphere summer. Note that the scatter index of almost 40% for the hindcast for July 1997 corresponds to an rms error that is as small as 0.2m. Because the Gulf of Mexico is an enclosed basin, wave conditions are dominated by wind seas. Because wind seas are more prone to forecast errors, error growth with forecast time in this area is much larger than in the deep ocean
In the NE Pacific Ocean (Alaska) the wave model generally behaves well with moderate biases and rms errors and with moderate hindcast scatter indices of around 18% throughout the season. Error characteristics (in particular the scatter index), are slightly better than average throughout the forecast period
In the NW Atlantic Ocean the wave model shows systematic negative biases, both in terms of bulk statistics and as a function of the wave height. This might be related to the fact that the local wave fields often are dominated by wind seas generated by offshore winds. In the GDAS and AVN, winds close to the coast might be expected to be underestimated due to the mixing of 'land' and 'sea' winds in this area. This might explain the systematic low bias. If this explanation holds true, the bias should be reduced with the introduction of higher resolution wind models. Another possible explanation might be found in the presence of the Gulf Stream. The rms errors in this region follow the composite dataset closely. Scatter indices are higher in the northern hemisphere summer due to the low average wave heights associated with this season
In the NE Atlantic Ocean the wave model tend to show positive biases for unknown reasons. A possible explanation is that at least one of the buoys (63111) is sheltered by the non-resolved Shetland Islands, but considering that this is only one of the eight buoys in this group this explanation appears unlikely
For the 1997/12-1998/02 period the composite buoy data set shows a positive bias both in terms of bulk statistics and as a function of the wave height. This behavior might be related to anomalous model behavior in the NE Pacific Ocean as is discussed with the satellite data below
For the period of mid June 1998 through early October 1998 serious errors occured in the prediction and analysis of tropical systems as described above. This translates in elevated error levels for the wave model, in particular at the buoys exposed to tropical wave systems (Japan, Gulf of Mexico, NW Atlantic)