After the value At, or AS ■, has been determined from the TS diagram, the total salinity and 

 temperature of the two upper mixed layers can be easily determined from the formulas given 

 above. We can judge the possibility of mixing with subsequent layers from the top in an analogous 

 manner. 



The solid curves in figure 16 show schematically the normal vertical distribution of tempera- 

 ture, salinity and specific volume at the initial moment; the dashed lines show the distribution of 

 these same factors after convective mixing from the sea surface to a certain depth, caused solely 

 by a drop in temperature; the crossed lines show the distribution caused exclusively by an increase 

 in the salinity of the surface layers. As can be seen from the figure, convective mixing as opposed 

 to frictional mixing, does not create large specific volume gradients, and accordingly, high stabil- 

 ity at its lower distribution boundary. In addition, convective mixing due to a temperature drop 

 usually creates a temperature inversion at its lower boundary. 



Figure 16. The vertical distribution of tem- 

 perature, salinity and specific 

 volume after convective mixing. 



Mixing, convective or frictional, does not occur instantaneously, but requires definite periods 

 of time for its completion. In general, it occurs more rapidly, the higher the negative stability 

 which determines its appearance. Actually, we can visualize the operating process of convective 

 mixing from the negative stabilities, sometimes observed in the surface, intermediate and deep 

 layers of the ocean. 



LITERATURE: 47, 62, 77. 



Section 30. Vertical Winter Circulation 



A drop in temperature of the sea surface layers (if we are examining water with a salinity 

 greater than 24. 7 o/oo) causes a decrease in the specific volume, and accordingly, if this decrease 

 is considerable, convective mixing. Therefore, in regions of the sea where the surface layers have 

 a sufficiently expressed diurnal temperature variation, we note during the day some temperature 

 increase (and thanks to evaporation, a certain increase in salinity as well), while at night there is 

 a cooling and convective mixing to a certain depth. This same phenomenon occurs during any tem- 

 perature drop in sea temperature. But this process reaches its highest development as a result of 

 extended winter cooling which causes the so called vertical winter circulation. In light of the spe- 

 cial significance of vertical winter circulation for the regime of the ocean, and in particular the 

 Arctic Basin, we will examine in more detail this phenomena. Since it is impossible to express the 

 relationships between temperature, salinity and specific volume by simple formulas, we will use an 

 arbitrarily selected example in the following discussion. 



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