588 H. MOHN. METEOROLOGY. [NORW. POL. EXP. 



THE DIURNAL AND ANNUAL PERIODS OF THE 



METEOROLOGICAL ELEMENTS IN THE ARCTIC 



CIRCUMPOLAR SEA. 



We have seen that the diurnal and annual periods of the meteorological 

 elements described above exhibit some features known from other parts of the 

 world, but also some features which seem peculiar to high latitudes and to the 

 low, flat ice-desert in which the Fram was drifting. In order to obtain a better 

 insight into the processes going on in the lower atmosphere in these regions, pre- 

 viously unexplored, processes resulting in the periods, I have found it appro- 

 priate to put together the following considerations. 



The main factor in these processes is the radiation from the sun. In 

 order to find an expression for the force and effect of this radiation, I 

 have made the following computations for each mean month of the drift of 

 the Fram (mean of 3 or 2 years). 



The mean latitude, g>, for each month has been taken from the Table on 

 p. 471; it is the mean latitude at noon. The declination, d, of the sun's 

 centre, is the mean of the declinations at mean local noon, computed from 

 the Tables of the Nautical Almanac. 



The altitude, a, of the sun's centre is 



at noon a = 8 + (90^) at midnight a = d (90 tp) 



The hour-angle, t, of the sun's centre, when the upper limb of the sun 

 is on the horizon, is found by the equation 



cos C sin m . sin 6 



cos J = 



cos cp . cos o 



