TM Wo. 377 



Spectrum 0U9 shows a further decrease in wave energy along with lower wind 

 speed. The low frequency peak (200 mcps) seen in 048 is still present and 

 relatively unchanged, whereas the high frequency peak at 300 mcps has decreased 

 markedly. In 052, where the winds have dropped to 5-2 m sec~l and shifted more 

 northerly, the high frequency peak (still at about 300 mcps) is still smaller. 

 The low frequency peak remains about the same as 0^9. Comparing 0U8, 0U9, and 

 052, it appears that the energy between 250 and 500 mcps was rapidly attenuated 

 as the wind decreased and shifted to a more northerly direction. 



By OUUO hours on 30 March, the wind was from the WNW at about 9»0 m sec~l. 

 The 053 spectrum shows that the low frequency peak at about 200 mcps has been 

 suppressed relative to the three previous spectra. The original band centered at 

 about 300 mcps has vanished, and a new peak has formed at about U00 mcps. This 

 latter peak is probably associated with the new wind waves generated by the freshen- 

 ing WNW winds. 



The 05U auto-spectrum shows a further suppression of the low frequency peak. 

 There is, however, an increase in the height of the band associated with wind 

 waves, which now is centered at about 350 mcps. 



By 11^0 hours (serial 057 B) the winds attained a speed of lU.O m sec"-*-. 

 The large wind waves are commensurate with the large variance of 1133 cm2 sec"2, 

 and show up clearly as a strong spectral pedestal centered at about 300 mcps. 

 There is a much smaller peak at 150 mcps. Actually, two sets of waves were 

 observed, one from the NW and another from the west. The latter waves were 

 apparently generated over the lower fetch (see figure IV-3). They are therefore 

 of lower frequency and have far less energy than the freshly developed waves 

 related to the high WNW winds. Note the similarity of the larger peak of 057B 

 with the peak of 032, both of which are attributed to relatively short-fetch 

 wind waves generated by relatively high winds. 



The BBELS-11 observations showed gross variations in the characteristic 

 auto- spectra of vertical wave motions. An attempt has been made to relate the 

 spectral shifts to observed wind and wave variations. The preceding commentary 

 of cause-and-effect is only a suggested simplified explanation of what is 

 obviously a very complex geophysical phenomenon. 



It was suggested earlier in this chapter that the variance, when measured 

 as a function of depth, can serve as an indicator of the vertical distribution 

 of kinetic energy associated with the wave motions. With this concept in mind, 

 let us examine the time-variable distribution of O^" 1 obtained in BBELS-11. 



Figure V-3^ shows the distribution of the variance OXu (in cm^ sec~2) as 

 a function of depth and time. It is instructive to compare this figure with 

 figure V-32. Between 1600 and 1800 hours on 29 March, the 0.5 meter and 2.0 

 meter variances are both relatively large (exceeding 1000 cm^ sec-2 and U50 

 cm2 sec-2, respectively). The winds at this time were about 9-12 m sec~l. 

 From 1700 hours on 29 March through 0500 hours on 30 March, both the 0.5 meter 

 and 2.0 meter variances display an overall decrease with time. This effect 



129 



