CURRENTS OF AIR AND OF WATER 



141 



equilibrium with the svurounding mass or 

 until they meet a denser substratum. Then, 

 if the supply of dense material continues, 

 they flow imder the lighter medium that 

 has been pushed aside in sinking. These 

 forces, acting on a global scale, whether in 

 the atmosphere or in the hydrosphere, tend 

 to set up planetary circulation in which air 

 (or water) rises in the tropics and sinks at 

 the cold poles. The currents of air are 

 known as winds; those of water are called 

 currents. 



currents of air or water can be statea 

 simply: If one faces down stream, or down 

 wind, this force causes currents that are 

 free to do so, to bend to the right in the 

 northern and to the left in the southern 

 hemisphere. Winds blowing toward the 

 equator, if they persist over long distances, 

 tend to blow from east to west, that is to 

 become east winds. Conversely, winds 

 blowing toward the poles, if similarly per- 

 sistent, tend to become west winds such 

 as prevail in middle latitudes. 



PRESSURE IN 

 ATMOSPHERES 



HEIGHT 



-50°C. 0°C. 25°C. 450°C. 



TEMPERATURE 



Fig. 25. General structure of the atmosphere. ( Modified from Wenstrom. ) 



The simphfied global system just out- 

 lined is comphcated by another potent 

 world force that acts similarly on wind and 

 on water currents and is called the deflect- 

 ing force of the earth's rotation. It is some- 

 times referred to as CorioU's force, after the 

 French physicist who first gave a mathe- 

 matical expression for it. The effect pro- 

 duced by the force of the earth's rotation on 



As a result of the interaction of these 

 two general sets of forces, a global system 

 of currents is estabhshed and maintained 

 both in the atmosphere and in the oceans. 

 The schematic systems are comphcated by 

 various other factors. For ocean currents, 

 some of the comphcations are ftunished by 

 the containing continents, by differences in 

 sahnity, and by the configuration of the 



