Wilker son 



about 69°W and the second at 73°W. The western edges of both meanders 

 are aligned very nearly north-south along 70''30'W and 73°30'W. The 

 meanders have heights of about 100 km and lAO km and describe a wave 

 length of about AOO km. 



Figure 4 shows the position of the boundary during October as 

 observed from ship by tracking the IS^C isotherm at a depth of 200 

 meters. The data were collected by a Coast and Geodetic Survey ship 

 of the Environmental Science Services Administration (ESSA) (Hansen, 

 1967) and are included for continuity, since no aircraft data were 

 available for October. The ship completed two tracking operations 

 between 13 and 22 October. The first from 13 to 17 October (solid 

 line) and the second from 18 to 22 October (broken line) . The posi- 

 tion of the boundary was shifting toward the east with a transla- 

 tional speed of about 3 n.m. per day or 6 cm/sec. The shape of the 

 boundary is similar to the aircraft boundary data of September. 



The wavelength of about 400 km is unchanged and the two meanders 

 are still evident with change in heights of both. The smaller mean- 

 der, now centered at about 72*'W, has decreased in height to about 35 

 km while the height of the larger meander has increased to about 200 

 km. 



Figure 5 shows the northern boundary as observed by aircraft on 

 14 November 1966. A continued shift of the boundary position toward 

 the east was observed between Cape Hatteras and 64*'30'W. The two 

 meanders can still be Identified. The smaller of the two is now 

 centered at about 71*'W, and the principal meander is centered at 

 about 68°30'W. Note that the western edge of the larger meander has 

 moved eastward more rapidly than the eastern edge, changing its shape 

 and causing a decrease in wavelength from 400 km to about 300 km. 



Figure 6 shows the Gulf Stream boundary as observed by aircraft 

 on 15 December 1966. The change in position and shape is apparent 

 from the continued shift of the two meanders toward the east and of 

 the changes in their height. The principal meander, now centered at 

 about 66**W, has increased in height to about 300 km; the smaller has 

 increased to about 100 km. The wavelength remains about 300 km. 



Figure 7 shows boundary data on 13 January 1967. The signifi- 

 cant change from December is seen in the eastward shift of the larger 

 meander, whereas the smaller meander has remained nearly stationary. 

 The shift has increased the described wavelength to about 500 km. 



CONCLUSIONS 



Figure 8 presents the five monthly boundary positions, four from 

 aircraft (solid line) and one from ship data (broken line) in a form 

 that lends itself nicely to an examination of the change in both 

 shape and position of the Gulf Stream frontal boundary. The vertical 

 separation of the data according to time is such that a 45-degree 



417 



