73°00'W. Although the eddy expanded considerably in size during the 
observation period, little lateral displacement occurred. 
The northern edge was observed outside Pickett's envelope during 
the flights of 3 and 9 April 1969 (figure 12), when the gradient was 
tracked on an easterly heading for approximately 110 kilometers from 
35°05'N,74°04'W to 36°05'N,72°05'W. The northern edge on 24 March and 
12 April (not shown) was located within the envelope. Thus, it can be 
concluded that the observed displacement, while of longer duration than 
the displacements discussed previously, probably occurred within a 10- 
to 14-day period. 
Slope Gradient 
A well-formed thermal gradient was observed adjacent to the Con- 
tinental Slope during all flights between 15 November and 3 April. 
The gradient may be located farther offshore in the southern part of 
the study area because of entrainment of the Shelf Water by the Gulf 
Stream. Numerous BT sections (not shown) taken by the authors along 
37°N between 73°W and 75°W indicate that the slope gradient is not evi- 
dent at the surface between late June and early November, undoubtedly 
because of surface heating. The gradient remains in evidence below the 
surface layer until destroyed by autumnal overturning. The limited 
salinity data available show a salinity gradient coincident with the 
thermal gradient with salinity less than 33.5°/oo inshore and greater 
than 34.5°/oo offshore of the gradient. The resulting density gradient 
undoubtedly inhibits mass transport across the front. 
MODEL 
A simple model of oceanic circulation offshore of the Virginia 
Capes which integrates the oceanographic phenomena discussed above is 
shown as figure 13. While admittedly simplified, the model is designed 
to provide oceanographic forecasters with basic concepts of water mass 
circulation to supplement a limited supply of synoptic data. 
The most dynamic feature of the model, of course, is movement of 
the Gulf Stream through the eastern part of the study area. SST near 
the northern edge of the Gulf Stream can be expected to be greater than 
21°C throughout the year. Change in SST across the northern edge ranges 
from about 2°C in summer to more than 12°C in winter with gradients of 
about 2° and 5°C/km, respectively. Frontal gradients and SST can be 
affected greatly through the presence of cold filaments and warm areas. 
Currents are generally northeasterly, with speeds approaching 2 m/sec 
in the near-surface layer. Mass transport varies considerably and may, 
on occasion, exceed 100 x 10°m3/see (Warren and Volkman, 1968). A 
temperature inversion often occurs in a thin filament immediately to 
the south of the surface indication of the northern edge, forming rela- 
tively strong sound channels. 
