127 



MM CHANGE IN DYNAMIC HEIGHT 

 I ) I + 



under such conditions are plotted in figure 51. From this it will be 

 seen that the surface velocity would be increased by the resulting two 

 to three millimeters increase in the gradient between stations 2715 

 and 2720. On the assumption made, a discontinuity surface would 

 exist at a depth of 100 meters. 



If the energy involved in such a change is to be considered, it is not 

 sufficient to deal with surface velocities 

 alone, but volumes of flow must be 

 examined. Just as in the upper part of 

 this 100-meter layer the velocities were 

 increased, so in the lower part the veloci- 

 ties were decreased even more. In the 

 numerical determination of the volume 

 of flow between stations 2715 and 2720 

 the effect of such mixing would be to 

 decrease the volume of flow by about 

 0.07 million cubic meters per second. 

 Thus it is seen that the result of such 

 hypothetical uniform adiabatic mixing 

 caused by the passage of a storm over 

 such an area is a decrease in energy of 

 the current system and an increase in 

 the surface velocity. It is suggested 

 that although the magnitude of the 

 resulting effect seems small in the in- 

 stance here examined, it may be of con- 

 siderable importance taken over pro- 

 tracted periods and in other localities. 

 It may be well to point out that the 

 foregoing considers only the effects of 

 internal density changes and not the 

 effect of tangential stress produced by 

 wind at the air-water boundary. 



The route synopsis and general descrip- 

 tion of the work undertaken on the 1938 

 post-season cruise has been given on page 

 115. Figure 52 shows the disposition of the oceanographic stations and 

 gives the dynamic topography of the surface. A reference surface of 

 2,000 decibars has been used since the extensive survey of 1935 indi- 

 cated that, at least in the southern part of the Labrador Sea, the depth 

 of the most nearly motionless surface was about 2,000 meters. The 

 effect of the shoal off Hamilton Inlet is shown on the Labrador side 

 and the West Greenland Current is evident rounding Cape Farewell. 

 The branch of this current which crosses to the American side south 

 of Davis Strait is to be seen intersecting the longitudinal section. 



2713 



Figure 51.— Change in dynamic height of 

 sea surface which would result if upper 

 100 meters were uniformly mixed. Sec- 

 tion across Gu)f Stream near fiftieth 

 meridian, June 3 and 4, 1938. 



