128 Meanders 



On the other hand, we have so httle consecutive data on the develop- 

 ment of a meander into an eddy that we are at a distinct disadvantage. For 

 example : after an edd}^ breaks off, does the parent stream mend itself, or do 

 the two ruptured ends remain broken, the severed fragment drifting away 

 to the northeast, and the fresh end penetrating to the east to form a new 

 extension of the Gulf Stream ? 



GULF STREAM MEANDERS 



The Gulf Stream meanders observed on the Multiple Ship Survej^ of June, 

 1950 (FugUster and Worthington, 1951), have inspired several theoretical 

 studies. It has been suggested that they are analogous to the waves in the 

 atmospheric jet stream, but both their small scale (100-400 km.) and their 

 small velocities of propagation suggest that the variation of the Coriolis 

 parameter with latitude is not a dominant factor in their djmamics. 

 HaurAvitz and Panofsky (1950) have constructed several models of currents 

 in a homogeneous ocean with cross-stream velocity profiles similar to those 

 observed in the true Gulf Stream, and have carried out an intricate pertur- 

 bation analysis to show the existence of unstable waves with reasonable 

 velocities of propagation. These waves are a result of the shearing instability 

 of the Stream. 



In a series of lectures at Woods Hole in 1954 on the stabUity of large-scale 

 motions Dr Jule Charney showed how appUcation of some meteorological 

 studies might be made to Gulf Stream meanders, in particular, the work of 

 Kuo and Phillips. Kuo (1949) has made an extensive study of the instability 

 of single smooth-profiled streams in a barotropic atmosphere (one in which 

 the pressure and density surfaces are parallel). The wavelength of maximum 

 instabihty in Kuo's theory is about 2-7 times the width of the stream, or 

 about 140 km. PhiUips (1951) has discussed the instabihty of a particular 

 baroclinic model (pressure and density surfaces intersecting) consisting of 

 two layers of equal thickness, one flowing over the other. For values of the 

 parameters similar to those of the Gulf Stream, the maximum instability 

 occurs for waves about 300 km. long, the rate of increase of amphtude, 

 about three times in two weeks. Neither of these models resembles the real 

 Gulf Stream very closely. Perhaps all we learn from them is that the Gulf 

 Stream viay he unstable, either barotropically or baroclinicaUy, or both. 



It seemed to me (Stommel, 1953) that certain types of meanders might 

 exist in which stratification and inertia are dynamically important. In 

 order to illustrate such a system, meanders in a very wide current were 

 studied. To simplify the analysis, the reaHstic cross-stream velocity profiles 

 of Haurwitz and Panofsky (1950) were abandoned. The density stratifica- 

 tion of the real ocean is approximated by a two-layer system. 



