OCEANIC CIRCULATION AND OCEAN-ATMO 1 1 IONS 



Hydrodynamic Modeling of Ocean Systems 



Waves and currents in the ocean 

 can be organized into many different 

 categories depending on horizontal 

 dimension and the time-scale of vari- 

 ability. Some of these categories are 

 strongly interconnected, others al- 

 most independent. In Figure IV-2 an 

 attempt is made at classification, along 

 with an indication of the principal 

 ways in which each phenomenon has 

 an impact on human activities. (The 

 emphasis in this outline is on ocean- 

 circulation phenomena; surface waves, 

 tides, and storm tides are treated only 

 briefly, although thev are admittedly 

 important subjects from the stand- 

 point of practical disaster-warning 

 systems.) 



Present Status 



Wind Waves and Tidal Waves — 

 The numerical models presently used 

 to predict surface waves are essentially 

 refinements of earlier operational 



models developed by the U.S. Navy; 

 they have proved valuable to ship- 

 ping. New computer models, how- 

 ever, allow a much more detailed in- 

 corporation of the latest experimental 

 and theoretical advances in the study 

 of wave generation. Furthermore, or- 

 biting satellites may soon be able to 

 provide a good synoptic picture of the 

 surface sea state all over the globe. 

 Given an accurate weather forecast, 

 computer models would then be able 

 to predict future sea states. Indeed, 

 it may turn out that the ultimate limi- 

 tation to wave forecasting will involve 

 the accuracy of the weather forecast 

 rather than the wave-prediction 

 model itself. 



Operational models for predicting 

 tidal waves (tsunamis) have been de- 

 veloped for the Pacific, where the 

 danger of earthquakes is greatest. As 

 soon as the epicenter of an earth- 

 quake is located by seismographs, the 

 model can predict the time a tidal 



wave will arrive. Such warning sys- 

 tems are being developed by the 

 National Oceanic and Atmospheric 

 Administration (NOAA) and the 

 Japanese Meteorological Agency. 



Storm Surges and Tides — Most of 

 the research in developing numerical 

 models to predict storm tides has 

 been carried out in Europe, in con- 

 nection with flooding in the North 

 Sea area. In the United States, storm 

 surges caused by hurricanes ap- 

 proaching the Gulf Coast have gener- 

 ated the most interest. The results of 

 these model studies appear promising. 

 Graphs and charts based on the 

 model calculations may be used by 

 Weather Service forecasters in mak- 

 ing flood warnings. The models will 

 also be useful in the engineering de- 

 sign of harbor flood-walls and levees. 

 In time, computer models will prob- 

 ably replace the expensive and cum- 

 bersome laboratory models of harbors 

 now used by coastal engineers. 



Figure IV-2 — CLASSIFICATION OF WAVES AND CURRENTS 



The chart classifies waves and circulations as functions of time and distance. 



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