During 9-11 August 1988, a cyclone developed over Uruguay in the lee of the Andes Mountains and moved over the South Atlantic Ocean, where it redeveloped into an intense storm. This storm was responsible for unusual wave activity along the Brazilian shoreline from 22Њ to 32ЊS. The Brazilian news media reported the loss of at least one life, waves of 3 m and higher, and the disappearance of a drainage pipe, which weighed 8000 kg, off the shores of Rio de Janeiro.In this paper, the evolution of this intense storm and the associated ocean wave response is studied through European Centre for Medium-Range Weather Forecasts analyses, a hydrostatic limited-area meteorological model, and a second-generation prognostic wave model.The atmospheric model results indicated the presence of a long-lived and large fetch with surface wind velocities higher than 12 m s 01 directed toward the coast. Some areas with velocities of 20 m s 01 were embedded in the fetch. The wave model forced by this wind field was able to simulate waves with a significant height of 8 m far from the coast and about 4 m in regions very close to the Brazilian coast in agreement with the occurrence reported at Rio de Janeiro. The swell propagation toward the coast of Rio de Janeiro was obstructed by a northeastward 10-m wind during the first 24-h period of the model's integration. During the second 24-h period, the fetch was still large and strong, but the obstacle was removed by a counterclockwise rotation of wind direction favoring the swell and windsea propagation toward the Rio de Janeiro coast.
ABSTRACT:With the aim of assessing the merits of the new source function proposed earlier in Polnikov (2005), it was tested and validated by means of the modification of the well known model WAVEWATCH-III. Assessment was done on the basis of comparing the wave simulation results found from both models against the buoy data obtained in three oceanic regions: eastern and western parts of the North Atlantic, and the Barenz Sea. First of all, incorporation of the new source function into the numerical codes of WAVEWATCH was done, and this modified version of WAVEWATCH was fitted and tested by standard tests. On the basis of these results some physical conclusions were drawn. Then, sophisticated fitting of the modified model was carried out, using the observation data of 19 buoys obtained in two regions of the North Atlantic for a period of 30 days at 1-hour time intervals. After this, the standard validation of both models was continued on the basis of the 8-month historical data, corresponding to 12 buoys located in the western part of the North Atlantic. Finally, comparative validation of the models was done against the wave observations obtained at one buoy in the Barenz Sea for a period of 3 years at 6-hour time intervals. Estimations of simulation accuracy were carried out for the three parameters of wind waves: significant wave height, H s , peak wave period, T p , and mean wave period, T m . Comparative analysis of these estimations was carried out for the original and modified model WAVEWATCH. The advantage of the modified model was revealed, with an increase of simulation accuracy for H s by 20 to 50% for more than 70% of the buoys considered. Additionally, it was found that the speed of calculation was increased by 15%.
The influence of ocean gravity waves on the wind and temperature above the surface is investigated using a one-dimensional boundary layer model. The effect of the wave-induced stress is evaluated using three parameterizations: wave age (WaAg), wave steepness (WaSt), and wind action on the wave spectrum (WiAc). It is found that while the WaAg is more effective in reducing the wind for young waves, in the WaSt approach the maximum reduction is for old waves. On the other hand, the WiAc is very sensitive to the energy present in high frequencies corresponding to periods less than 2 s, which are found in both young and mature spectra. Since observations show that most of the wave stress is due to the small-period wave energy, in this aspect the WaSt parameterization is not recommended; WaAg is not as accurate; and thus WiAc is the best among the three, although its computational cost is the highest.The droplet load contribution to the total surface stress can be neglected for the droplet spectrum produced by 10-m wind speeds up to 15 m s 21 , but its importance increases with the speed and its magnitude becomes about 1 /5 of the total stress for wind speed ;30 m s 21. Concerning the latent and sensible heat fluxes accompanying the production of spume droplets by waves, a feasible microphysical formulation for operational use in weather forecasting models is proposed. The droplet spectrum is assumed to be a product of two functions, one depending on the windsea Reynolds number and the other on the droplet radius spectrum. The bulk effect of the latter is analytically evaluated and stored in a table as a function of air temperature T a , relative humidity R % , and significant wave height H s . In numerical experiments with initial sea surface temperature 5 K higher than the air surface, latent and sensible heat contributions to the air temperature are computed as a function of the wave spectra. The launched droplet spectrum (which increases the air temperature due to sensible heat) and the relative humidity (which controls the cooling due to the droplet evaporation) define the heat budget and the air temperature evolution. Although in these experiments the sea temperature is much higher than the air temperature, the results show a noticeable dominance of the evaporative cooling in the lower atmosphere mainly for smaller significant wave height. Some air warming is noticeable only from a threshold around H s $ 5 m.
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