Paper 15 



free imagery indicates that Gulf Stream eddies are common in the 

 Slope Water region east of zone 1. It appears/^ therefore/^ that 

 eddies formed east of zone 1 (off the central Scotian shelf) tend 

 not to move westward very far. No eddies observed during 1976r 

 in the area of our analysis/^ originated east of zone 2. 



A westward boundary to the region of eddy formation is apparent 

 in the zonal analysis. During 1974-76^ no eddies originated west 

 of zone 5 . 



ENVELOPES OF EDDY CENTER POSITIONS AND BOUNDARIES 



Envelopes drawn around all the observed surface center positions 

 and surface boundary positions of eddies during 1976 appear in 

 Figure 15.16. The narrow portion of the envelope of centers 

 between 69W and 72W reflects the fact that few eddy observations 

 were made in this region. 



DISCUSSION 



Satellite ima.gery has proved itself an effective means of 

 monitoring anticyclonic eddies but does have inherent 

 limitations: 



1. Imagery reveals what is happening at the surface/ but 

 the surface is the last place to become disconnected in 

 anticyclonic eddy formation fGotthardt 1973)/ whereas the 

 area of maximum energy may be over 100 m below the surface 

 (Khedouri and Gemmill 1974). Thjs/ a feature located near 

 the Gulf Stream may appear as a meander in satellite 

 imagery/ while the main body of water beneath the surface 

 circulates as an eddy. 



2. During the summer/ surface temperatures ir the Slope 

 Water may approach that in the eddies/ causing the latter to 

 "disappear" in the imagery. This effect probably contrib- 

 uted to eddy 76C's not being detected until mid-August 

 (Fig. 1 5.3) . 



3. The region of our analysis is subject to long periods of 

 cloudiness during which eddies may be formed or destroyed. 

 Potocsky (1976)/ in an evaluation of imagery over the entire 

 western North Atlantic/ found that cloud free coverage was 

 best during April and October and worst during December. 



A- Eddy surface expression can be distorted by entrained 

 Shelf Water (Potocsky 1976). Chsmberlin (see footnote 3) 



266 



