can be substantiated or altered based on the isen- 

 tropic flow patterns. Parr (193Sb) objected to 

 some interpretations, on the part of Ice Patrol, 

 of the dynamic height charts used for iceberg drift 

 predictions. Parr's isentropic analysis near the 

 southern end of the Banks tended to show a large 

 pooling tendency which was not shown on the 

 dynamic charts. This pool is now generally 

 accepted as a quasi-fixed feature. Parr's work 

 did show that better water movement infonnation 

 could be obtained from isentropic analysis, how- 

 ever the discrepancies that he found were much 

 greater than can be discovered using present day 

 data collection techniques. Prior to World War 

 II the sparseness of station data coupled with 

 technique diff'erences probably accounted for a 

 weakness in the dynamic height charts. 



Good comparisons can be seen between the 

 circulation deduced from the isentropic charts 

 and the dynamic height charts shown in figures 

 2A and 5A. Where the dynamic height charts 

 present quantitative current information, futvu'e 

 changes are reflected in the isentropic charts. 

 Figures 15A to 18A indicate that cold water was 

 entering the system during the first survey, and 

 ultimately was seen to have a definite circulation 

 effect based on data obtained on the check survey 

 conducted only 8 days later. This cold water 

 intrusion from the north is not indicated in the 

 dynamic height charts. Basically, the direction 

 of flow of the dynamic height and the isentropic 

 charts match very nicely in all areas. Figure 2A, 

 shows an area of uncertainty, indicated by dotted 

 streamline, in the northwest section current pat- 

 tern deduced by dynamic heights, ln)wever, the 

 sigma-t surface of 26.7, figure 15A, distinctly 



' shows the water flowing onto the Banks in that 

 i 



area. A cyclonic flow pattern is defined by the 



dynamic height streamlines based on third survey 

 data, figure 5A, in the southeast quadrant of the 

 survey area. A look at the isentropic charts sub- 

 stantiates this circulation. Several sigma-t levels 

 definitely show the cyclonic circulation with water 

 of low temperature and low salinity entering from 

 the east. This is incongruous with the water types 

 usually found in the Atlantic Current and it can 

 be concluded that this is a closed cell which prob- 

 ably had its origin from the cold water pool nor- 

 mally found at the Tail-of-the-Banks as shown in 

 figure 2A. Ijooking at the 26.6 a, level, figure ISA, 

 the cell appears separate from the general near sur- 

 face How. On this level, water of 11.0° C. enters 

 from the east which is anomalously warm and is 



probably near surface water being entrained from 

 the warmer layers of the Atlantic Current. 



At the 26.8-tr, level, figure 19A, the cell remains 

 quite warm and shallow and affected by the 

 warmer surface water movements. A slight 

 indication of upwelling is seen now from the 

 temperature lowering near the center of this 

 cyclonic circulation with warmer water at the 

 periphery being drawn around the eddy. 



The 27.0-0-, level, figure 20A, reflects active 

 upwelling in the eddy center not only by colder 

 temperatures, but also by a definite dome in the 

 depth of the sigma-t surface. Warmer water of 

 the Atlantic Current appears to be moving anti- 

 cyclonically around the eddy in a northwesterly 

 dh-ection. Although it is not shown in these 

 illustrations, the data indicates not only a cooling 

 of the eddy waters but also a reduction in salinity. 

 On this level, the coldest water appears to be 

 displaced slightly to the north from the 26.8-0-, 

 level. The 27.2-0-, level, figure 2lA, is incon- 

 clusive as to whether or not a circulation connection 

 exists with the northwest meander of the Atlantic 

 Current cited above. In this situation the eddy 

 does not appear to be closed. Although isotherm 

 contours do not indicate the circulation in the 

 case of the 27A-(j, and 27.6-(r, levels, figures 22A 

 and 23A, the topography of the sigma-t surfaces 

 again show that the cyclonic circulation seems to 

 be causing some upward movement of the water 

 in the eddy. 



In conclusion, it has been shown tliat isen- 

 tropic analysis is an excellent tool for depicting 

 details of the circulation in the vicinity of the 

 Grand Banks. The presentations would be more 

 accurate if a nondensity related property such as 

 oxygen was used. For Ice Patrol current pre- 

 diction procedures, it appears that detailed analy- 

 sis of this nature is not warranted in all areas on a 

 routine basis, however, to completely define and 

 predict the Labrador's variation, the cold water 

 core should be examined with this method. 

 Because the water moves along sigma-t surfaces, 

 the intrusive flow of the Labrador Current water 

 is clearly shown by the isotherms in contrast to 

 the rather nondescript presentation of the hori- 

 zontal levels. The method is probably most 

 valuable for observing the trend of future condi- 

 tions, since water masses of differing charac- 

 teristics wliich ultimately influence the entire 

 area can frequently be traced from their point of 

 original entry. 



11 



