• April — Forty-three surveys (no data from 

 196<)) 



• May — Forty -five surveys (no (iala from 

 lasr) ami l!)6i)) 



• June — Twenty-nine surveys (no data from 

 1941, 1951, 19r)7, 1963, 1965, 1966, 1969-1971) 



• July — (no data prior to W^V II nor from 

 1949, 1950, 1954, 1958, 1959, 1965, 1966, 1968- 

 1972). 



The July chart is somewhat abbreviated coverinji 

 only a small area east of Cape Bonavista. From 

 19;M tlirouijli 197'2, no other areas were surveyed 

 durin<i July. 



Data for the revised charts were processed 

 exactly in the same manner as described by 

 Soule (1964). Briefly, dynamic height values, 

 dynamic hcijrht of the sea surface relative to the 

 1000 decibar surface, for each survey were com- 

 puted at twenty minute intervals of latitude and 

 lonjritude in the area surveyed. The dynamic 

 heifihts at each interval were averaged for each 

 month with equal weight given to each year 

 rather than each survey. These average values 

 were used to develop the monthly normal charts 

 (figs. 41, 44, 47, 50). A standard deviation was 

 computed at each interval. All locations with 

 at least five surveys were used to contour a field 

 of standard deviation for each month (figs. 42, 

 45, 48, 51). Finally a chart for each month 

 (figs. 43, 46, 49, 52) was prepared which indi- 

 cates data distribution and computed results at 

 each interval according to the following format: 



Inrtivkiual 

 Surveys 



Standard 



IH'viiition in 

 n.vnaniic Milli- 

 niotpr.s 



General Comments 



Years 

 Represented 



Average Dynamic Heigiit of the 

 Sea Surface Relative to tlie 

 1,000 Peciljar Surface in 

 Dynamic Meters minus 970.00 



The Labrador and North Atlantic Currents, 

 as well as a region of low dynamic topography 

 between them, are clearly present on the April, 



May, and June normal charts. Using informa- 

 tion from recent (""anadian Ilydrographic Service 

 charts, it is clear that the bottom topography 

 affects the flow of both currents. The steepest 

 gradients of the Labrador Current closely par- 

 allel the bottom contours along the eastern slope 

 of the Grand Banks implying that the Grand 

 Banks acts as a lateral boundary of this current. 

 The flow of the North Atlantic Current is in- 

 fluenced as it passes over and around the north- 

 ern end of the Newfoundland Ridge which is 

 located south of the Tail of the Bank. 



Current direction can be inferred quite real- 

 istically from the normal charts as being parallel 

 to the isopleths of dynamic heights. However, 

 geostrophic speeds are not as easily determined. 

 Due to the averaging process, speeds calculated 

 by taking measurements perpendicular to the 

 isopleths of dynamic height are lower than those 

 that actually exist in the Labrador Current. 

 Thus the current as calculated from the noiTnal 

 charts only approaches a maxinmm of 40 cm/sec 

 in a few extreme cases in the core of the Labra- 

 dor Current. "Wliereas experiments such as those 

 conducted by International Ice Patrol (direct 

 measurement by parachute drogues) in 1966 

 (Wolford, 1969) indicate the speed of the Labra- 

 dor Current actually varies from 50 to over 100 

 cm/sec. Thus when using the normal charts, 

 one must be careful not to underestimate the 

 current speed. 



The fact that these revised charts closely re- 

 semble Soule's adds validity to the assumption 

 that the general circulation in this area is basic- 

 ally the same from year to year. This is espec- 

 ially true for the core of the Labrador Current 

 and the dynamic "trough" to the east of this 

 current. Standard deviations are greatest near 

 41°N, 50°W and 42.5°N, 46°W. These are the 

 areas which contain meanders of the North 

 Atlantic Current. Annual changes combined 

 with steep gradients result in standard devia- 

 tions being as high as 20 centimeters in May. 



