structure could be developed. These oscillations, the so- 

 called Internal wave, are the subject of the following section 

 of the report, 



C. Investigation of periodic variations due to Internal 

 waves 



1, Introduction 



The problem of periodic oscillations of the water 

 masses in the oceans has been treated by various authors in the 

 past, and more and more attention has been given this phenomenon 

 in recent years with the increasing realization of the important 

 role these waves play in the determination of the thermal struc- 

 ture. The problem of isolating these waves from other processes 

 operating in the ocean is not a simple one; one of the facts 

 that has become evident to all investigators of internal waves 

 is that these waves com.plicate the actual motion greatly and 

 cause extremely varied and intricate distributions of currents 

 and vertical motions e 



In general the problem has been approached in two ways. 

 The first is the simpler linear theory first treated by Stokes 

 (Lamb, 1932) in which it is assumed that the wave occurs along 

 the discontinuity surface between two layers, each homogeneous 

 and each of different density. The more complex problem of 

 progressive internal waves in a heterogeneous medium in vfhich 

 density is a continuous function of depth has been attacked 

 vjith considerable success by Pjeldstad (1933) and others. In 

 oceanography both models have their applications, and therefore 

 both have been -considered in this inyestigation, 



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