604 



H. MOHN. METEOROLOGY. 



[NORW. POL. EXP. 



the early morning hours, and maximum some hours after noon; but the 

 range varies greatly in the different months (p. 471). The range does not 

 increase and decrease with the diurnal range of the radiation from the sun 

 and sky, except from March to April and from August to September. The 

 range rises to a maximum in April, sinks to a minimum in July, reaches a 

 smaller maximum in August, and sinks again in September. 



The main factor checking the radiation of the sun is the clouds, and in 

 cloudy weather a stronger wind is also (p. 294) to be found. Putting together 

 from the Tables on pp. 476 and 480 the range of temperature (R), and the 

 amount of cloud and wind-velocity (v), we have the following Table. 



In spring, ten degrees of increasing cloudiness lowers the range of tempera- 

 ture from 2'°10 to l-°72 or 0"°38, while in summer 5'5 degrees of cloudiness 

 (10—4-5) lowers the range from l-°22 to 0°89 or 0°33. One degree of cloud- 

 iness lowers the range as much as 0"°038 in spring and 0'°060 in summer. 

 The summer clouds seem to be thicker and denser than the spring clouds, a 

 conclusion to which we have arrived through the discussion of the diurnal 

 period of the velocity of the wind (p. 601). 



An increase in the velocity of the wind of 3 metres per second lowers 

 the range of the temperature as much as 0°3, both in spring and in sum- 

 mer. The wind brings the higher layers of the air down during the day 

 hours (p. 603) and prevents the stagnation of the air at the surface of the 

 earth that has been cooled during the night by radiation from this surface 



