INTENSIVE DYNAMIC SURVEYS 



The three consecutive Intensive STD Surveys 

 conducted during June and July 1^73 provided 

 a unique opportunity for a detailed study of 

 oceanic circulation. A near-synoptic survey was 

 made possible by the close station spacing in 

 time and space. Taking note of the location and 

 station density (fig. 1) of the approximately 

 122 X 111 km station grid, it is evident that the 

 horizontal distributions of physical properties in 

 this area, where the North Atlantic and Labrador 

 Currents meet, would be more adequately defined 

 by an intensive survey than by a survey consist- 

 ing of only the Ice Patrol standard sections. 

 The limited area covered by the surveys allowed 

 for complete coverage in approximately three 

 days, with repeated occupations within about 5 

 days (Table 3). 



The calculation of ocean currents based upon 

 relative dynamic depth anomalies has several 

 limitations which detract from their reliability 

 as estimates of true flow for certain areas of the 

 Grand Banks (Kollmeyer, 1967). The under- 

 lying assumptions that conditions are steady 

 state and that a dynamic equilibrium exists be- 

 tween the horizontal pressure gradient force and 

 the Coriolis force do not apply where other forces 

 have an important role. This is particularly true 

 on the continental slope and outer shelf where 

 bottom friction and wind induced sea surface 

 slopes alter the mean flow from its baroclinic 

 equilibrium assumed by geostrophy. 



Aside from the inapplicability of simple geo- 

 strophy to the slope/shelf region, the means by 

 which the surface dynamic depth anomaly is de- 

 termined may compound the error. To determine 

 the western wall of the Labrador Current it is 

 necessary to make geostrophic current calcula- 

 tions in water shallower than the shelfbreak. 

 To do this, the procedure previously referenced 

 of extending the temperature and salinity iso- 

 pleths horizontally into the continental slope is 

 employed. These extrapolated data are then 

 combined with the data from the measured water 

 column above to determine a surface dynamic 

 height to be used in surface current calculations. 

 All stations shallower than the reference level of 

 1000 decibars are treated in this manner. For 

 each section extending perpendicular to the conti- 

 nental shelf a new set of extrapolated tempera- 

 ture and salinity values are derived. Conse- 

 quently, when these different values are applied 

 to the calculation of dynamic heights there exists 

 an upstream-downstream slope to the isosteric 

 surfaces which have been extended horizontally 

 into the continental slope. Consequently, there 

 is an apparent flow into or out of the bank which 

 we know cannot be correct. 



A table of comparison has been prepared for 

 the Intensive Surveys which illustrates the mag- 

 nitude of error caused by the use of this method 

 (Table 4). 



TABLE 3 



Intensive Dynamic Surveys 



