Origin 



Some theory regarding the origin of internal waves 

 exists. One school of thought believes that internal tides 

 originate directly from tidal forces. According to this 

 idea, the internal waves begin at a frequency equal to the 

 tidal frequency but at wavelengths of free waves. Another 

 opinion contends that internal waves originate when currents 

 pass over bottom irregularities. Origin by this process 

 would be particularly noticeable in the region of the shelf 

 break. Model experiments with two-layer systems indicate 

 that internal waves start where such changes of bottom 

 topography occur. Modeling systems without jump layers, 

 that is, with arbitrary but stable density distribution, have 

 evidently not been attempted. 



Mathematical analysis of shear currents in the 

 ocean leads to still another possible origin for internal 

 waves. The analysis indicates that under certain idealized 

 conditions, a nonbalanced velocity field in the process of 

 adjusting toward geostrophic flow can lose energy to oscil- 

 lating modes. 



Although some recent progress has been made, 

 almost nothing is known of nonlinear interactions. For 

 example, shear currents might produce internal waves. 

 Conversely, the question arises as to whether shear will 

 reduce the coherence of waves as they travel through shear 

 layers and feed energy back into the nonperiodic motion. 



Some recent developments indicate that steady or 

 low-frequency surface tides flowing over a rough bottom 

 will originate internal waves. On the other hand, it is not 

 known whether energy will be fed back and forth between 

 frequencies as internal waves progress over it. From the 

 standpoint of theory, nonlinear interaction between different 

 kinds of motion and different frequencies is perhaps the 

 greatest gap in present knowledge. 



Both modeling and mathematical analyses indicate 

 that internal waves can originate from atmospheric dis- 

 turbances, but this possibility does not seem to be too well 

 accepted among the investigators. All of these are reason- 

 able theories for the origin of internal waves in 



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