Because the SSF is so close to shore in the Cape Hat- 

 teras area, and many of the transects ran parallel or at 

 highly oblique angles to the front, the position of the 

 front is not as easily detectable as it is in the Middle 

 Atlantic Bight (to be discussed later). However, a few 

 good examples of the front showing how it develops 

 through late winter and spring should be pointed out. 



Santa Cruz (App. Figs. 27 and 28) crossed the SSF 

 right at Cape Hatteras where the shelf water, slope 

 water, and Gulf Stream meet. These crossings that oc- 

 curred in January and February, respectively, show how 

 the thermal structure develops as the coldest months of 

 winter progress. At this time of the year, when the shelf 

 waters were coldest, the interaction and mixing with 

 Gulf Stream waters created a very distinct thermal front. 

 The Santa Cruz (App. F'ig. 30) again crossed the front 

 just north of Cape Hatteras (between stations 17 and 18) 

 showing a strong temperature gradient near the mixing 

 region of the three water masses. 



Two crossings were obtained in September, one by the 

 Mormac Argo (App. Fig. 36) and the other by the 

 USCGC Taney (App. Fig. 37). At this time of year the 

 thermal gradient was not as strong as earlier and sea sur- 

 face salinity was the more accurate frontal indicator. 



Also in October the Mormac Argo (App. Fig. 42) cros- 

 sed the SSF in the vicinity of an anticyclonic eddy. The 

 thermal structure of the front was effectively masked by 

 the presence of the eddy and the sea surface salinity 

 values were essential for locating the front. 



In December the Santa Cruz (App. Fig. 45) crossed the 

 SSF again in the vicinity of an eddy. Although the ther- 

 mal structure of the front was not as disrupted as in the 

 previous month, it was still necessary to utilize the sea 

 surface salinity as an indicator of the frontal position. 



Low salinity surface water.— Utilizing water of 

 <34.57o. as the boundary between coastal or shelf water 

 and the more oceanic water or slope water, it was possi- 

 ble to monitor positions of the SSF when thermal 

 gradients were mixed or confused. When surface or sub- 

 surtace temperature data were not available, the 34. 5%, 

 isohaline was used to determine the SSF with con- 

 fidence. Often when satellite imagery was poor or nonex- 

 istent and when temperature stratification was strong, 

 the surface salinity data was the only reliable data 

 available for determination of the shelf water-slope water 

 boundary. 



In 1975 SOOP vessels transected coastal water of 

 <34.5%. in the Cape Hatteras area on 12 occasions (see 

 Table 7 and App. Figs. 27, 28, 30-32, 34, 36, 37, 41, 42, 45, 

 and 46). The data were used independently and 

 sometimes in conjunction with sea surface temperature 

 data to determine the exact position of the SSF. 



Eddies.— These XBT sections include only three 

 crossings of Gulf Stream eddies in the Cape Hatteras 

 area during 1975 (see Table 8 and App. Figs. 39, 42, and 

 45). Eddy number 1 (App. Fig. 39) was an anticyclonic 

 eddy crossed by the Santa Cruz on 24 September and 

 was centered along this transect at station 11 (lat. 



Table 7. — Low salinity (<34.5V.= ) coastal water encountered by 

 SOOP vessels in the Cape Hatteras area in 1975. 



30°50'N. long. 75°.36'W). There was little, if any, surface 

 expression reflected in the surface parameter plot (App. 

 Fig. .39) and most of the temperature structure was found 

 beginning about 100 m and becoming stronger at 300 m 

 and below. 



Comparison with the September 1975 issue of 

 dulfstream indicated agreement in location with an anti- 

 cyclonic eddy shown on 10 September. 



Eddy number 2 (App. Fig. 42) was an anticyclonic 

 eddy crossed by the Mormac Argo on 31 October and was 

 centered along this transect at station 5 (lat. 37°35'N, 

 long. 69°55'VV). There was a definite increase in sea sur- 

 face temperature and salinity over the center of the eddy 

 providing a good signal for satellite imagery. Comparison 

 of this transect with the November 1975 issue of 

 dulfstream and with the Experimental Ocean Frontal 

 Analysis Chart for 29 October- 1 November 1975 did show 

 good agreement in both the location and areal extent of 

 the eddy. 



Eddy number 3 (App. Fig. 45) was a cyclonic eddy 

 crossed by the Santa Cruz on 7 December and was 

 centered along this transect at station 16 (lat. 36°26'N, 

 long. 74°18'W). There was definite surface expression in 

 both temperature and salinity which peaked within the 

 eddy. The decrease in sea surface temperature and 

 salinity on the southern side of the eddy indicated the 

 possible entrainment of shelf water along its northern 

 and eastern edges. Comparisons made with the Ex- 

 perimental Ocean Frontal Analysis Chart (10-24 

 December 1975) produced by the Naval Oceanographic 

 Office agreed well in position and with the possible 



Table 8. — Eddies transected in the Cape Hatteras area b> SOOP 

 vessels in 197.i. 



App. 



Fig. 



Ship 



Cruise Station 

 number number 



Date 



Diameter 

 n.mi (itm) 



39 Santa Cruz 

 42 Mormac Argo 

 45 Santa Cruz 



75-09 9-13 9/24-25 C 90(167) 



75-10 4-7 10/31-11/1 A- 115 (213) 



75-12 18-13 12/7 A 50(93) 



'C=cyclonic. 



'A = anlicvclonic. 



