A shallow water intercomparison of three numerical wave prediction models (Swim)
ABSTRACT Three operational shallow water wave models are intercompared for two artificial experiments and verified for a severe storm hindcast, with the objectives of further understanding the effects of the parametrization of shallow water wave processes in numerical models.The models used are the HYPAS (Max-Planck Institute) and GONO (KNMI) coupled-hybrid models, and the BMO (Meteorological Office) coupled-discrete model which are all briefly described. In the first case, depth-dependent fetch-limited wave growth in a steady wind is examined. In the second case a steady onshore wind is specified over an idealized constant slope coastal shelf, and the stationary wave spectra at various depths are intercompared. For the third case the wind fields for the North Sea storms of 18-26 November 1981 were accurately reconstructed and used by each model in its operational configuration to produce a wave hindcast for this period.In case 1 the GONO and BMO models exhibit similar behaviour in the evolution of energy and peak frequency, whereas HYPAS displays less depth attenuation and little variation in peak frequency. In case 2 the energy values at different shelf depths are approximately as predicted in case 1 for HYPAS though rather higher for BMO and GONO. However, GONO and HYPAS show little change in peak frequency with depth here whereas BMO wave spectra become double-peaked with a wind-sea peak migrating to higher frequencies in shallower waters. In case 3, the hindcasts, all models produce qualitatively similar results. the time series of wave height and period agree well with measurements, BMO and HYPAS predicting correct energy levels except at storm peaks and GONO generally overpredicting both at lower energy levels and in a duration-limited strong wind case. the r.m.s. error in wave height at the southern shallow water verification site is 0.5 m for all models, and varies between 0.9 m (GONO) and 1.5m (HYPAS) at the northern deep water site. Some wave spectra are presented and the directional relaxation of wind-sea in each model is illustrated.The results of cases 1 and 2 are readily explained by the formulation of shallow water processes adopted in each model, but it is difficult to isolate and identify these mechanisms in the measured or modelied spectra from the hindcast. It is suggested that future studies involving detailed verification and intercomparison of wave models should be confined to more carefully designed wave-measuring experiments so that less ambiguous results are obtained.
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ABSTRACT: This paper continues the description of surface waves on finite depth water started in Bouws et al. . We present relationships between the parameters of the wind wave spectra similar to the correlation found in deep water between total energy and spectral peak frequency. In contrast to deep water the peak frequency is not the most convenient parameter to describe spectral development. The wave number of the spectral peak, however, is connected with other spectral parameters by relations that are independent of water depth or site. Diese Arbeit setzt die Beschreibung von Oberflächenwellen im Flachwasser fort, wie sie bei Bouws et al.  begonnen wurde. Es werden Relationen zwischen den Parametern der Windseespektren aufgezeigt, ähnlich der Wechselbeziehung, die im Tiefwasser zwischen Gesamtenergie und der spektralen Peak-Frequenz entdeckt wurde. Im Gegensatz zum Tiefwasser ist die spektrale Peak-Frequenz nicht unbedingt der passende Parameter, um die spektrale Entwicklung zu beschreiben. Die Wellenzahl des spektralen Peaks ist jedoch mit anderen spektralen Parametern durch Relationen verbunden, die unabhängig von der Wassertiefe sind. Cet article poursuit la description des vagues de surface en eaux de profondeur finie commencée dans Bouws et al. . Nous présentons les relations entre les paramètres des spectres des vagues générées par le vent similaires à la corrélation trouvée en eaux profondes entre l'énergie totale et la fréquence de pointe spectrale. Contrairement à ce qui a été observé en eaux profondes, la fréquence de pointe n'est pas le paramètre le plus adapté pour décrire le développement spectral. Le nombre d'onde de la pointe spectrale est cependant relié à d'autres paramètres spectraux par des relations qui sont indépendantes de la profondeur d'eau et du site.Ocean Dynamics 12/1986; 40(1):1-24. DOI:10.1007/BF02328530 · 1.68 Impact Factor
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ABSTRACT: With the object of providing an accurate set of open‐sea wave spectra in a variety of conditions, we deployed, in conjunction with CASP, an array of 9 wave buoys (3 directional, 6 non‐directional) along a 30‐km line offshore from Martinique Beach, N.S. A large set of high‐quality wave spectra was collected in conjunction with extensive meteorological information. The data set is unique in the sense that a large onshore swell component was normally present.Offshore‐wind cases for three windows: ±5°, ±15° and ±30° with respect to the shore normal, have been considered. Wind speed was found to be a strong function of fetch, and attempts were made to allow for this in the analysis. Power‐law regressions have been produced of dimensionless sea energy, peak frequency and high‐frequency spectral level (the Kitaigorodskii “alpha” parameter) vs dimensionless fetch and wind speed (inverse wave age). The regressions are compared with earlier work: the Joint North Sea Waves Project (Jonswap) and the Canada Centre for Inland Waters (CCIW) Lake Ontario study.The comparisons indicate that dimensionless wave energies, peak frequencies and alpha values in this experiment are comparable with those from earlier experiments; in spite of different wind analysis methods, the CASP and CCIW fetch‐limited growth laws are consistent within the contexts of the two experiments. Differences among the estimated parameters are as large within the analyses of the three windows as they are among the three experiments we compare.Atmosphere-ocean 03/1989; 27(1):210-236. DOI:10.1080/07055900.1989.9649334 · 1.19 Impact Factor