DYNAMIC TOPOGRAPHY AND CURRENTS 



Since the distribution of temperature and salinity is 

 strongly indicative of the existence of generally stationary 

 conditions throughout much of the area studied, it would be 

 expected that quite satisfactory current determinations could 

 be made from dynamic computation, providing a suitable 

 level reference surface were found. This latter requirement 

 cannot be met, however, for the area in general is less than 

 50 meters deep and the pressure surfaces are apparently 

 inclined relative to the level surfaces at all depths. Dynamic 

 computations suffice only in indicating the flow of the surface 

 relative to some deeper level, here taken at 45 meters. The 

 results indicate, however, that the dynamic topography gives 

 the direction and relative magnitude of the surface flow quite 

 well, though the absolute magnitudes of the currents as obtained 

 from the dynamic computations are lower than the magnitudes 

 of the observed currents. 



The dynamic topography, based on the dynamic height 

 anomaly of the surface over 45 decibars, is shown in figure 51. 

 In order to use 45 decibars as a reference level, it was neces- 

 sary to extrapolate the data for several stations, using several 

 reference stations as guides. It was found that the final value 

 for the dynamic anomaly was not greatly affected by the 

 manner in which this extrapolation was performed. 



The solid arrows on figure 51 show the direction of drift 

 of the USS NEREUS during several periods when the ship was 

 allowed to drift with the current and the wind. Because the 

 vessel has a high freeboard, it is likely that the drift is greatly 

 affected by the wind. This is seen most clearly at the drift 

 stations taken at the edge of the ice pack, where the dynamic 

 topography indicates a northerly flow. The USS NEREUS 

 drifted southeastward, however, at a speed of about l/2 knot. 

 This drift was largely related to the observed northwest wind 

 of about 7 knots, for the drift was observed to be southward 

 relative to the pieces of floating ice which surrounded the 

 ship at the beginning of the drift. 



The observed velocities of drift at stations N8, N9, and 

 the five stations in Bering Strait gave directions which were 

 very close to the direction of flow indicated by the dynamic 

 topography. However, the computed velocities were in every 

 case much smaller than the observed velocities (approxi- 

 mately l/lO as large). This is to be expected since the bottom 

 waters also are apparently in motion to the north. Some of 

 the difference between observed and computed currents in 

 Bering Strait can be related to wind drift of the ship, for the 



