150 THE OCEAN RIVER 



conductors of heat and cold — soil is warm below frost, and 

 cool beneath rocks too hot to touch. Therefore this energy 

 is almost at once transformed into heat and returned to the 

 atmosphere; and this is why the land becomes quickly cold at 

 night. But sea temperatures change little from day to night, 

 because the turbulent water quickly passes a share of incoming 

 solar heat to the layers beneath and thus becomes a store- 

 house, a moving reservoir that can carry heat poleward to 

 parts less well endowed by the radiant energ}^ of the sun. 



All that immediately concerns us in following the story 

 of the weather and climate is that the Ocean River carries 

 heat and in turn affects the air above and conditions our lives. 

 People are often concerned lest a change in the Gulf Stream 

 might be responsible for unusual weather in the United 

 States. But this could be so only indirectly, since in the 

 Atlantic States our prevailing weather is continental — coming 

 from inland. Yet an increase of a permanent nature in the 

 warm, humid atmosphere of the Stream might well result in 

 sucking down cold high-pressure waves from the Arctic. Be- 

 cause of this, a radical, warmer change in the Stream, while it 

 would warm Europe, would probably cool off our Atlantic 

 seaboard. 



The atmosphere is divided. Up to about six miles above the 

 earth we have the troposphere, then a demarkation called 

 the tropopause, and above that the stratosphere. In the tropo- 

 sphere around and above us the temperature drops as we go 

 higher; above it in the lower parts of the stratosphere the 

 temperature is relatively constant and cold. There is one essen- 

 tial variation in these layers. The stratosphere begins at nearly 

 10 miles above the equator but is only about 5 miles above 

 the pole. This is because the sun strikes full upon the tropics, 

 whereas at the pole its rays are oblique, spread thin, and poor 

 in heat. With greater warmth from the land and sea below 

 to act on it the tropical air expands and rises; the polar air 



