Recent Research Accomplishments 



New methods for measuring the siirtaee 

 temperatures and currents, together with 

 more precise methods of navigation, have 

 revolutionized our concept of the Gulf 

 Stream. Analysis of older observations sug- 

 gested that it was a broad, sluggish cur- 

 rent, with a rather stable course, but it has 

 proven to be much narrower and to have 

 large eddies that form and disappear along 

 its boundaries. Still more recently, mathe- 

 matical analysis has given new insight 

 into the dynamic interactions that cause it. 

 A balance of the forces resulting from 

 the east-west winds, the rotation of the 

 earth, and the dissipation of energy in the 

 form of variable eddies, causes oceanic 

 currents to concentrate in narrow regions 

 on the western sides of the oceans. The 

 currents on the eastern sides, in contrast, 

 may be much broader and less well defined. 



The theoretical approach also appears to 

 afford a means for obtaining a unified hy- 

 drodynamic theory of physical oceano- 

 graphy. In the early work, fluids were 

 usually assumed to be homogeneous. Strat- 

 ification due to the change in temperature 

 and salinity with depth, such as exists in 

 the ocean, was neglected. Recently it has 

 been recognized that calculations omitting 

 the effects of systematic differences in den- 

 sity of only a few percent between the 

 surface and the deepest bottom are often 

 completely wrong. 



Another recent theoretical development, 

 stimulated by the practical needs of aero- 

 dynamics, is in the study of turbulence. 

 The "frittering away" of large orderly mo- 

 tions by the development of successively 

 smaller unstable eddies occurs in the ocean 

 on an entirely different scale than in wind- 

 tunnels, and is strongly influenced by strat- 

 ification. Equally important in the ocean 

 is another process that is somewhat the 

 converse of this: the generation of the major 

 ocean currents by steady winds. If a wind 

 begins to blow over initially calm water, 

 its first effect is to ripple the surface. Wave- 

 lets appear and grow. If the wind is strong 

 and continued, the waves are accompanied 

 by the transport of large masses of water. 

 When the winds are steady in direction the 



accompan)'iiig transport gives rise to the 

 major ocean currents. Mathematically, the 

 conversion of small waves into large cur- 

 rents is analogous to the conversion of 

 large currents into small eddies. The gen- 

 eral regime of the oceans must depend on 

 a balance between the two processes. 



Underwater acoustics has been the chief 

 reason for the Navy's recent interest in 

 physical oceanography. The permanent 

 sound channel at mid-depths which is pres- 

 ent over much of the ocean provides an 

 effective means of acoustical transmission 

 over great distances, as has been demon- 

 strated in the air-sea rescue system known 

 as SOFAR. Since the physical character- 

 istics of the environment frequently become 

 the limiting factor in underwater sound 

 transmission, the Navy has encouraged 

 basic studies in physical oceanography. As 

 instrumentation in underwater acoustics has 

 improved, sound in turn has become a pri- 

 mary means of exploring the ocean. It has 

 been used for some time in determining the 

 depth. Now it is being used effectively for 

 exploring the geology of the ocean basins, 

 and the use of sound holds great promise 

 as a means of gaining quantitative infor- 

 mation on the distribution of the larger 

 animals in the sea. Acoustical techniques 

 are also promising as a precise means of 

 navigation. 



Much interest in recent years has cen- 

 tered on the problem of predicing the 

 height and period of sea, swell, and surf 

 from the weather situations prevailing over 

 the oceans. Knowledge of wave processes 

 has increased to the point where meteorol- 

 ogy, rather than oceanography, has become 

 the bottleneck in the further refinement 

 of wave forecasting. It is now evident that 

 there may be certain advantages to the 

 reverse procedure, to use observations on 

 the period and height of swell to fill in 

 details on the weather map in distant areas 

 where the swell was generated. This is a 

 particularly promising weather forecasting 

 technique in the southern hemisphere 

 where weather observations from over the 

 ocean are widely spaced or entirely missing. 



