606 H. MOHN. METEOROLOGY. [noRW. POL. EXP. 



From June to July the same process goes on. 



From July to August the range of radiation rises (the mean latitude of 

 the Fram being relatively lowered), and the amount of cloud and the velocity 

 of the wind decreases. The temperature-range rises, all three factors working 

 together. 



From August to September the range of radiation is going down rapidly, 

 the amount of cloud and the velocity of the wind are increasing, and all 

 three factors cause the range of the temperature to decrease. 



We see that the maxima of the diurnal range of the temperature in both 

 April and August, correspond with a higher range of the radiation, and 

 minima of cloud and wind-velocity. 



The low range of the temperature in summer, particularly in July, corre- 

 sponds to a high degree of cloudiness during a season which has hardly one 

 clear day. 



The annual period of the temperature of the air has been discussed on 

 pp. 484 and 597. In general it follows the annual period of the radiation from 

 the sun and sky, with a certain amount of lag. The minimum of the tempe- 

 rature falls at the beginning of February, and the maximum in the middle 

 of July, while the radiation has its minimum and maximum at the solstices. 



The winter temperatures and the lowest temperatures found on the 

 track of the Fram (pp. 483—487 and PI. XIV and XVI) are higher than 

 those found at the Siberian cold pole. In Siberia the low temperatures are 

 due to calms and inversions of temperature. The soil is frozen down to a 

 great depth \ In the circumpolar arctic sea, calms are relatively rare (p. 283), 

 cyclonic movements are frequent (p. 581), the upper and lower layers of air 

 are mingled together, and the cooling down of the surface of the earth or of 

 the polar ice is checked (p. 565 and PI. X) by the circumstance that the 

 underlying water has a temperature of only — 1"°6. 



The summer temperatures along the track of the Fram reaching above 0° 

 are due to warmer winds. The temperature of the surface of the ice cannot 

 become higher than 0°, and the water in the open pools scarcely higher, being 

 enclosed by ice below and around. The thermal wind-roses (p. 495) give south- 

 erly winds with a temperature of above 0° as the warmest in July and August, 



1 WoEiKOF. Die Klimate der Erde. Kap. 



