INTRODUCTION 



It was shown by A. Defant' in 1950 that internal tides strongly 

 influence the hydrographic situation in the area off California. Since 

 then, various measurements were made of internal waves in this area/"" 

 but the studies did not produce details of the modes of these internal 

 tides, nor of their origin and direction of progress in the open sea. 

 Studies of near-coast areas'""^ showed that no constant phase lag exists 

 between surface tides and internal tides. In 1963, Summers and Emery' 

 cohducted a multiple-ship study in the area off southern California, and 

 on the basis of their measurements formulated a very reasonable picture 

 of the semidiurnal tidal waves in that area. However, their values for 

 phase velocity are not in complete agreement with the values derived from 

 the theory of internal waves. For instance, their recorded component of 

 the phase velocity is about 9 knots in deep water and 0.6 knot over the 

 shallow shelf — values corresponding to about 4.6 meters/sec and 0.31 

 meter/sec. A reasonable value for the first mode, according to hydrody- 

 namic theory, would be 1.6 meters/sec for the semidiurnal wave. The 

 reason for this discrepancy seems to be that Summers and Emery disre- 

 garded the diurnal internal tides, which play an important role in their 

 records, as can be seen immediately in those from the R.V. Velero IV 

 and USS EXCEL. 



The study to be reported here was undertaken to gain a broader 

 understanding of internal tides — their natural movements, and the effects 

 of doppler shift upon the direction of their propagation. The areas studied 

 included various points off southern California and a long section from 

 San Diego to the Hawaiian Islands. 



The data were obtained by use of the NEL thermistor chain," a 

 towed instrument which records nearly continuous temperature data from 

 the surface to a depth of about 230 meters. The measurements are re- 

 corded in analog form as depths of isotherms. Depending on the informa- 

 tion sought, the towing ship followed an X-pattern, drifted, or lay at 

 anchor. 



The following sections will present: (1) development of equations 

 necessary for the analysis of the doppler shift of internal waves, (2) 

 development of an equation expressing the nature of free and forced in- 

 ternal tides in the open sea, (3) analysis of the chain data collected from 

 towed, anchor, and drifting stations off southern California, and (4) anal- 

 ysis of the chain data in a long section from San Diego to the Hawaiian 

 Islands. 



'Superscript numbers identify references listed at end of report. 



