Direction and velocity, their changes with depth, and the mean mass trans- 

 port of a pure wind current are very uncertain; consequently, locations 

 and rates of convergence and divergence are even more difficult to deter- 

 mine. Permanent dynamic factors undoubtedly exert considerable influence 

 on vertical motion of water produced by a transitory wind field and may 

 strengthen, reduce, or even destroy convergence or divergence rates, 

 thereby masking convergence or divergence in areas where it might usually 

 be expected. 



The vertical component of motion in an area of convergence increases 

 mixing energy, resulting in an increase of the mixed-layer thickness. Rise 

 of the thermocline and a dome-shaped conformation of isopycnal surfaces in 

 an area of divergence are due to upwelling. 



k values were determined by means of Equation (6) using known mean 

 mixed-layer thickness and wave parameters. Plotting of these values 

 against the sea state parameter 17 for given At intervals revealed anoma- 

 lous deviation of some points: some deviated upward; others, downward 

 (Figure 23). These points could generally be identified with areas that 

 suggest convergence or divergence with respect to the distribution of high 

 and low pressure areas, and their associated wind fields. Figures 2k and 

 25 show typical examples of areas assumed to be convergent or divergent. 

 Most scattered points of k(7j) usually coincide with such areas; however, 

 effects of convergence or divergence are not always evident. 



Increase of mixed-layer thickness due to convergence occurs most often 

 at the rear of a slowly propagating cyclonic field (Figures 2k and 25). 

 Strong convergence may develop between two cyclonic areas as shown in 

 Figure 25B. A convergence effect also usually develops at the center of 

 a high (Figure 2^B). In general, convergence is stronger when pure wind 

 current counters the permanent flow; convergence may not occur if direc- 

 tion of the pure wind current coincides with that of the permanent flow. 

 In contrast, divergence usually occurs at the center of a low or at a 

 slowly propagating front where wind direction changes sharply, as shown 

 in Figures 2^A and 2kB. In general, divergent conditions are more diffi- 

 cult to determine or justify by existing distribution of the wind field 

 than are convergent conditions. 



Each ocean area (some of which are perhaps 5 degrees or less square) 

 possesses individual geographic characteristics which affect formation of 

 the mixed layer and thermocline. In some cases, such as in areas of perma- 

 nent convergence or divergence, these characteristics may be sufficiently 

 strong to preclude conventional mixing processes. Beyond such extreme 

 cases, local effects are assumed as always present in some degree, acting 

 in different proportions and ways from one area to another. Local conditions 

 seem to be especially effective on mixed-layer changes due to convergence 

 or divergence. Actually, local factors probably exert initial influence 

 on convergence and divergence resulting in a chain effect on the mixed 

 layer. 



^7 



