Chapter 13 — CIRCULATION OF THE ATMOSPHERE 



6 MONTHS NIGHT 

 AT N. POLE 



TANGENT 



TANGENT 



6 MONTHS 

 DAY AT N. POLE 



6 MONTHS 

 DAY AT S. POLE 



SUN RAY 



6 MONTHS 

 NIGHT AT S. POLE 



22 DECEMBER-WINTER SOLSTICE 



SUN RAY qV^ 



21 JUNE-SUMMER SOLSTICE 



12 H 



TANGENT 



ANTARCTIC CIRCLE 



12 H SUN RAY 



21 SEPTEMBER-AUTUMN EOUINOX 

 21 MARCH- SPRING EOUINOX 



POSITION OF PERPENDICULAR AND TANGENT 

 SUN RAYS DETERMINES TROPICS OF 

 CANCER AND CAPRICORN AND ARCTIC AND 

 ANTARCTIC CIRCLES 



POSITION OF DAYLIGHT CIRCLE DETERMINES 

 LENGTH OF DAY AND NIGHT 



Figure 13-8. — Latitude differences in amount of insolation. 



210.3 



rates, the location of continents and oceans 

 greatly alters the earth pattern of air tempera- 

 ture and influences the sources and direction 

 of movement of air masses. 



Influence on Air Temperature. — Coastal 

 areas take on the temperature characteristics 

 of the land or water to their windward. In 

 latitudes of prevailing westerly winds, for 

 example, west coasts of continents have oceanic 

 temperatures and east coasts have continental 

 temperatures. The temperatures are determined 

 by the windflow. 



Since the upper layers of the ocean are 

 nearly always in a state of violent stirring, heat 



losses or heat gains occurring at the sea sur- 

 face are distributed throughout a large volume 

 of water. This mixing process sharply reduces 

 the temperature contrasts between day and night 

 and between winter and summer over oceanic 

 areas. 



Land surfaces are not subject to such a 

 mixing process, and the effect of conduction is 

 negligible. Thus, violent contrasts between sea- 

 sons and between day and night are created in 

 the interiors of continents. During winter, a 

 large part of the sparsely incident solar radia- 

 tion is reflected back toward space by the snow 

 cover that extends over large portions of the 



301 



