Article

A shallow water intercomparison of three numerical wave prediction models (Swim)

Quarterly Journal of the Royal Meteorological Society (Impact Factor: 3.33). 08/2007; 111(470):1087 - 1112. DOI: 10.1002/qj.49711147011

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.

1 Bookmark
 · 
73 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Surface waves play an important role for the sediment distribution in the shallow Baltic Sea. This paper presents the large-scale spatio-temporal distribution of wave-induced bottom friction velocity, u*, based on modelled wave data for the years 1999 and 2000. The highest values of u* are found along the eastern coasts of the Baltic Proper and Bothnian Sea—areas characterised by long fetches for the dominant winds. Temporally, the dynamics follow that of the wind climate with higher velocities during winter and lower during summer.A smooth bottom is assumed for the calculations. To test this assumption, u* is compared to other estimates of u* assuming rough bottoms. The spatio-temporal patterns are similar, although the present approach gives a slight underestimation of u* at areas with coarse grain sizes.To compare the results, the co-variation between the u* distribution and bottom type distribution from a digitised sediment map is analysed. It shows upon a good agreement. This is also found when comparing critical levels for resuspension found in the literature with the same from modelled u*. In addition, other processes important for bottom stress, such as mesoscale eddies and coastal jets, are discussed.
    Continental Shelf Research 01/2005; · 2.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To develop a simple method to predict the significant wave height, we analyze 18 years of hourly observations from 12 different buoys that are off the northeast coast of the United States. Water depths ranged from 19 to 4427 m for these moored buoys. We find that, on average, all of these buoys exhibit a region of constant wave height for 10-m wind speeds between 0 and 4 m s−1. That wave height does, however, depend on water depth. For wind speeds above 4 m s–1, the wave height increases as the square of the wind speed; but the multiplicative factor is again a function of water depth. We synthesize these results in a prediction scheme that yields the significant wave height from simple functions of water depth and 10-m wind speed for wind speeds up to 25 m s–1.
    Ocean Engineering. 01/2007;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The third generation of the SWAN wave model is modified by the incorporation of new resistance laws for hydrodynamically rough, incompletely rough (smoothly rough), and smooth underlying surfaces. A modified model is used to determine the functional dependences of wave parameters (such as the dimensionless energy of waves and the dimensionless spectral peak frequency) on a dimensionless fetch. The results of calculations are compared to the experimental data obtained in Lake George (northeastern Australia), which has a nearly constant depth and extended, nearly rectilinear segments of coast. The SWAN model is shown to depend weakly on hydrodynamic properties of the sea bottom: distinctions arising from changes in hydrodynamic properties of the sea bottom are smaller than the variances of experimental estimates.
    Izvestiya Atmospheric and Oceanic Physics 11/2008; 44(6):781-786. · 0.73 Impact Factor