right and left to determine the electrical zero of the instrument by 

 reversals of the electrodes with respect to the ocean current and to main- 

 tain the base course as the average course through the water. Instru- 

 ment log entries were made at each jog, giving the new zero, the two 

 rectangular components of the ocean current and their resulting vector. 

 At least approximate flow lines are needed in any current chart for 

 ice patrol purposes, and the area to be covered is so large that sections 

 cannot be spaced closely enough to permit the construction of flow lines 

 from vectors alone. For the construction of such flow lines a method 

 was devised which it was hoped could be used ultimately for equivalent 

 dynamic cartography in the outer portion of the area, and for the test 

 period was the basis of comparison of the results of the two methods. 

 In dynamic topography a current represents a gradient in dynamic 

 height in a direction ncnnial to the current. The current C may be 



expressed as : n ^tmo t ■ 



C = AD/2 coL sm ^„i 



where AD is the difTerence in dynamic height between two points 

 separated by a distance L and located at a mean latitude (pm- w is 

 the angular speed of rotation of the earth. When convenient units are 

 used and C is expressed in nautical miles per hour, L in nautical miles 

 and AD in dynamic meters, this becomes: 



C' = AD/0.01391 L Bin^m. 



which can be restated as AZ) = 0.01391 LC sin (^/». 



In this form it is convenient to compute the equivalent difTerence in 

 dynamic height between any two points from observed components of 

 the current normal to the line connecting the points and the distance 

 between them. 



During the season and post-season cmises the current meter was 

 operated between oceanographic stations at which the dynamic heights 

 were deteimined from the vertical density distribution. If A represents 

 the equivalent difference in dynamic height between a pair of stations as 

 computed from the above formula using as current the average of half- 

 hourly current meter indications, and B represents the difference in 

 dynamic heights derived from density distribution at the stations, 

 (A-B) is a measure of the discrepancy between the two methods, and the 

 cumulative algebraic sum of these discrepancies 2 (A-B) is the amount 

 by which the two methods woukl disagree if the computation were 

 carried along a section from a connnon starting point. 



The values of (A-B) were computed for each of 155 intervals lietween 

 pairs of stations and, arrangcnl in the form of the several sections in 

 which the stations were disposed, plotted with the resulting values of 

 2(A-B) against distance along the section. Some of these sections which 

 exemplify the results of the tests are shown in figure 38. The average 

 intervals between stations was 22.3 nautical miles. With errors in the 

 curient meter measurement of about 0.05 knot and in distance between 



94 



