Fluctuations 



137 



concerning Key West, Miami, and Cat Key, there are now available, for the 

 first time, tide-gauge data for Havana, This information is obtained from 

 a gauge set up by the United States Coast and Geodetic Survey in 1946. 

 A leveHng survey has been made between Key West and Miami (Mont- 

 gomery, 1941a), but it is, of course, impossible to connect Havana or Cat 

 Key to the same datum by ordinary means (Montgomery, 1947). Therefore 

 we cannot obtain true differences in sea level across the Straits, but we 

 can obtain fluctuations in the differences of sea level at two stations, as 

 shown in fig. 70. At all four stations the maximum sea level occurs in 



O O HAVANA — KEY WEST 



fl A CAT KEY — MIAMI 



X X HAVANA — CAT KEY 



a a KEY WEST — MIAMI 



Fig. 70. Annual changes in the difference of sea level between various 

 of stations on the Florida Straits. From Stommel (1953, fig. 1). 



pau-s 



September and October, apparently caused by the summer heating of the 

 water. This average rise does not appear in the differences. 



One interesting feature of these differences is that the fluctuation in the 

 Miami-Cat Key differences is about twice that of the Key West-Havana 

 differences. The maximum cross-stream slopes occur during July, when the 

 flow is strongest (Hela, 1952), and the maximum downstream slope from 

 Key West to Miami also occurs at this time. These relations of slopes to 

 surface velocity are quite what might be expected from the most elemen- 

 tary considerations of Bernoulli's equation and the geostrophic equation 

 (see Chapter III). But the fact that the fluctuations of the differences at 

 the Miami-Cat Key section are larger than at the Key West-Havana 

 section, and the fact that the downstream slope between Havana and Cat 



