characteristic of this geographical 

 region: (1) prevailing easterlies; 

 (2) winter cold fronts; and (3) 

 tropical storms (Warzeski 1976). 

 These energy levels (discussed in 

 greater detail in the section on 

 climate) provoke unique current 

 responses of temporal and spatial 

 variability discussed in the follow- 

 ing sections. 



The prevailing easterlies, 



characterized by a low energy level 

 (low to moderate wind velocity) of a 

 long term nature, originate as the 

 name implies from the east (SE to 

 NE) (Cruber 1968). These winds pro- 

 vide a "background condition" onto 

 which the remaining two energy 

 levels are superimposed. Winter 



cold fronts bring nigh winds of a 

 sustained nature (3 to 4 days) that 

 rotate the resultant wind vectors in 

 a clockwise 360° manner and reach 

 3 m/sec (26 ft/sec). As the front 

 passes, higher winds from the north- 

 west reach 10 to 15 m/sec (33 to 

 49 ft/sec) and have been reported 

 as high as 20 to 26 m/sec (66 to 

 85 ft/sec) (Multer 1977). The third 

 energy wind level is produced by 

 tropical storms which in the most 

 intense form, hurricanes, produce 



Months 



Dec -Feb 

 Max -May 

 June-Aug 

 Sept -Nov 



Resultants- 

 Direction 



/ 



winds ranging from 33 m/sec (108 

 ft/sec) to over 100 m/sec (328 

 ft/sec) (Gentry 1974). As the oc- 

 currence of a hurricane is rare 

 (1 chance of occurring every seven 

 years), the effect of these events 

 on the current patterns will be 

 treated separately in a later 

 section. 



Enos (1977) summarized in Table 

 18 the resultant wind vectors, con- 

 stancy, and velocity for the Florida 

 Keys area. These wind vectors re- 

 present the synergism of all winds 

 on a seasonal basis, dominated usu- 

 ally by the first two energy levels 

 (prevailing easterlies and synoptic- 

 scale fronts). From September- 

 November (fall) and December-Febru- 

 ary (winter) the influence of the 

 cold fronts produces the northerly 

 component to the resultant northeast 

 winds as well as an increased mean 

 wind velocity. The summer and 

 spring months typically exhibit 

 lower velocity winds coming from 

 east and southeasterly directions. 

 The response of currents to the 

 winds reflects the temporal vari- 

 ability of the winds on a seasonal, 

 monthly, and even daily basis 

 (Hanson 1980). 



Constancy 



30-50 



35-50 



30-60 



4-60 



Veloc i ty ( knots ) 



12 



8 

 10 



^Resultant is a vector of frequency and average force, averaged for two (2) 

 5° areas over 3 months. 



instancy is the percentage of time that wind blows from the quadrant 

 containing the mean. 



Table 18. Summary of wind data from the Florida Keys (adapted from 

 Enos 1977). 



90 



