602 



H. MOHN. METEOROLOGY. 



[NORW. POL. EXP. 



wind belongs to a cyclonic state of the weather. In cyclones the ascending 

 currents give rise to condensation of aqueous vapour and the formation of 

 clouds. The clouds intercept the radiation from the sun and sky, and tend 

 to lower the range of the diurnal period of the velocity of the wind; but the 

 stronger wind that produces the clouds, gives a greater range. The latter 

 seems to be the more powerful, except in the summer months when the clouds 

 are thickest and densest. 



The fresher and freshest winds (pp. 305 to 307, PI. I) have a diurnal 

 period with maximum in the day hours and minimum in the night. 



Putting together the means for the seasons, we obtain the following table: 



In winter the range of radiation is small and the sky fairly clear; the 

 range of the velocity of the wind is small. 



From winter to spring the range of the radiation increases rapidly, the 

 amount of cloud increases, but the former prevails over the latter, and the 

 range of the velocity of the wind increases. 



From spring to summer the range of the radiation is increasing, but the 

 increasing amount of clouds, and their thickness and density, prevail over 

 the radiation, and the range of the velocity of the wind decreases. 



From summer to autumn the range of the radiation decreases, but the 

 wind's velocity increases, and the sky becomes clearer; the range of the 

 velocity of the wind increases a little. 



From autumn to winter the range of the radiation decreases, the wind's 

 velocity decreases, the sky becomes clearer, and the range of the velocity of 

 the wind decreases. 



The diurnal range of the velocity of the wind generally follows the in- 

 crease and decrease of the range of the radiation, except in summer, when 



