variations is expressed as an algebraic sum of variations induced by processes that act 

 simultaneously. 



The temperatures and salinities that are created in surface layers by intermixing are trans- 

 mitted downward to a certain depth, thus creating the so-called "active layer." 



Depending on local circumstances, this layer can be completely uniform. At other times, the 

 curves of vertical distribution of oceanological characteristics in the active layer are very com- 

 plex. Besides, this layer can be either thick or thin. 



The main distinguishing feature of the active layer is the fluctuation of oceanological charac- 

 teristics (within the limits of accuracy of the observations). These fluctuations can be diurnal, 

 seasonal, secular or of some other period. Evidently, the longer the given time period, the 

 greater the thickness of the active layer. 



The intermixing processes that create the active layer are discussed in detail in the sub- 

 sequent chapter. Here is suffices to point out that if the density of surface layers increases with a 

 change of temperature and salinity in the layer, a convective intermixing is induced as a result. 

 Otherwise, the static equilibrium of water layers is not disturbed, and external factors need be 

 added in order to induce intermixing, notably: the wind, tidal phenomena, currents, etc., which 

 induce the movement of water layers relative to one another in the sea. The intermixing that is 

 induced by external forces can be called a frictional intermixing (occurring as a result of friction 

 relative to one another) . 



LITERATURE: 62, 67. 



Section 13. Solar Radiation 



Solar energy is a primary source of all phenomena occurring on the earth. The quantity of 

 sunlight and heat that reaches the earth depends on the geographical latitude and varies with vari- 

 ations of astronomical and meterorological conditions. The quantity of heat annually transmitted 

 by the sun to the earth could melt a layer of ice 36 in. thick covering the entire surface of the 

 earth. 



out: 



At high latitudes (beyond the Arctic Circle), the following astronomical seasons canbe singled 



1. arctic winter - the sun does not rise above the horizon, 



2. arctic spring - the sun rises and sets daily, but the length of the day is increasing, 



3. arctic summer - the sun does not disappear at all, 



4. arctic autumn- the sun rises and sets daily, but the length of the day decreases. 



The nearer to the Arctic Circle (away from the Pole), the shorter is the arctic winter and 

 the arctic summer; the nearer to the Pole, the shorter the arctic spring and the arctic autumn. 



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