figure 7.1 show that the wind speed have values of 2Z knotS; 17 ..;nots, 19 

 knots, 20 knotSj, 19 knots, 17 knotSj 20 knots, and 17 knots between 0200,Zv 

 and 1200Z on the day of the observations.. Thereafter the wind died down 

 and fluctuated between 13 and 15 knots until after the observations were 

 completed at I8OOZ0 



The Neumann theory of wave generation require? a duratiora 01 8,3 hours 

 and a fetch of 55 NM in order to produce a fully developed sea at 18 knots, 

 and a duration of 10 hours and a fetch of 75 NM to produce a i'ully developed 

 sea at 20 knots, An average of the wind speeds from 0400 to 1230.; , as read 

 at half-hour intervals from the lines connecting the actual observa.t;ions, gives 

 an average wind speed of about 18 = 7 knots which compajres favorably with the 

 values used aboveo The duration of 9 hours would be enough to p;.oduce a 

 fully developed sea at this wind speed, and it certainly seems plausible that 

 the fetch was at least 75 NM. 



Over the ocean area upwind of the point of observation (a distcvnce of 

 about 250 NM) it can be stated that due to turbulent variations ir the wind 

 there should be areas of the dimensions of 50 to 75 NM where the mean wind 

 speed would vary over a range from 17.5 to 19 knots a.s averaged ovei- the 

 nine or ten hours previous to the time that the winds died down at the 

 ATLANTIS station. 



Then, given a decrease in wind speed, each of tlie areas would have to 

 be treated according to the methods of Pierson, Neui-nann and James [1955] 

 as if it were a Filter IV case and the spectrum at the point where the obser- 

 vations were made reconstructed. 



140 



