in computation of p values (Figure 23). Consequently, these curves must 

 "be considered to represent well-developed strong convergence or divergence 

 effects on the mixed layer. In cases of -weak or moderate convergent or 

 divergent effects on the mixed layer, interpolations can be made "between 

 normal and convergent or divergent values. Successful interpolation depends 

 considerably on experience and knowledge of local conditions. 



h Curves 



The broken-line curves in Figures 15 through 22 are used for determin- 

 ing the mixed-layer thickness h and were computed by Equation (7) after 

 application of Equation (6) to determine k values for the various At inter- 

 vals with known mixed-layer thickness and given wave parameters. After 

 determination of the k(^) curves, k values along with given wave parameters 

 and the sea state parameter 77 were considered to be known, h values could 

 then be computed and plotted as curves related to the k(7j) curves. The 

 central h curve applies to normal mixing, the upper h curve applies to 

 convergence, and the lower h curve applies to divergence. Mixed-layer 

 thickness h is measured in feet and can be determined by means of the right 

 half of the scale in the left margin of Figures 15 through 22. Inter- 

 mediate values for weak or moderate convergent or divergent effects on the 

 mixed layer may be interpolated between the normal and convergent or diver- 

 gent values. 



The h curves rise quite steeply for low 77 values, rise less steeply 

 with moderate values, and finally level off at high 17 values. This level- 

 ing off occurs only with rather high 77 values at low stability indexes. 

 With high values of stability index, leveling off begins for moderate values 

 of 77. The normal h curve for the At of 2 F is almost horizontal at an 

 approximate 77 value of 620. This value of 77 corresponds to a fully developed 

 sea in a wind field of 38 or 39 knots, where mixed-layer thickness is about 

 310 feet. Further increase of wind force would not appreciably increase 

 the mixed-layer thickness, if normal conditions (no convergent effect )_ 

 persist and At remains constant. In case of convergence the limit of h 

 for the At of 2° F is about ^50 feet at an 77 value of 885, which corre- 

 sponds to about 43-knot winds and fully developed sea. 



The normal h curve for the At interval of 17° F levels off when 77 

 equals 170, which corresponds to about 27-knot winds and fully developed 

 sea. With such stability under normal mixing conditions (no convergent 

 effect), further increase of wind force would not increase the mixed-layer 

 thickness. Mixed-layer thickness at the At of 17° F is thus limited to 

 80 feet; the thickness could increase to about 135 feet, when 77 is 270 in 

 the presence of a strongly developed convergent effect. 



All h values and their limits apply only when AT is constant. If the 

 mixed-layer thickness increases rapidly, At does not usually remain con- 

 stant. A mixture of cool water from the thermocline decreases the mixed- 

 layer temperature and simultaneously decreases 5£, so that the initial AT 

 value does not apply during the entire active mixing period. Lower At values 

 must be substituted near the end of the mixing period; consequently, mixing 



52 



