536 



Internal Waves 



of first to fourth order. The computation gives the amplitudes of the vertical 

 displacements and horizontal velocities as relative values, which are plotted 

 on an arbitrary scale. The observations give us absolute values. Further- 

 more, the theory gives the velocities of progress of these waves of different 



o 



100 



200 



6 300 



| 400 



D 



500 

 600 



o> =26 



27 



28 







100 



200 



300 E 



400 g 



500 



600 



Fig. 223. Left: vertical distribution of the density a t and vertical distribution of the vertical 

 displacements r\ of the internal waves of the 1st until 4th order at the "Michael Sars" Sta- 

 tion 115. Right: vertical distribution of the amplitudes of the horizontal velocities corres- 

 ponding to the internal waves of the l-4th order, ri and u are in arbitrary units (Fjeldstad). 

 (The reader may note that in the picture to the left C stands for rj.) 



orders provided that the depth remains constant and that the distribution 

 of density remains constant in the direction of progress. For this station 

 the velocities are (in cm/sec): 



d = 70 



c 2 



39 , c 3 = 26 and c 4 = 19-5 . 



The theory does not give the periods or the phase of the waves. Both must 

 be obtained from observations. In this case, the wave lengths of the internal 

 waves, corresponding to waves of 24 lunar hours (diurnal tide wave), will be 



23-2 and h 



17-4 km. 



K = 62-5 , h = 34-8 , ;. 



The internal tide waves are thus considerably shorter than the tide waves 

 at the surface. The velocity of progress of the internal tide waves will possibly 

 be greater in the open ocean than in the case just discussed, because the 

 velocity of progress of internal waves increases where the difference in density 

 between the upper and lower layers decreases, and also increases with in- 

 creasing depth to the bottom. The velocity of progress of the wave of first 

 order will seldom exceed 300 cm/sec. For diurnal or semi-diurnal tide waves 

 the corresponding wave lengths will then be about 270 and 135 km respectively; 

 for waves of a higher order they will be correspondingly shorter. If several 

 of such waves occur simultaneously, there is quite a confusion in the time 

 variations of the vertical displacements of the water masses and their cor- 

 responding currents. 



