55 



KIKKK1.AN1). THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902-1903. 



As an upper limit for the storminess which is not of solar origin we obtain 



For Matotchkin-Schar a = 5'J - 3 % = 1.1 y 



Kaafjord . . . a = Sf - *% = 0.4 



Axeloen a = S^ - % = 9.4 



Dyrafjord a = Sf - / 15 - 2.2 



In table CVI is given the lower limit of sun-storminess (5<? a) as compared with n and also 

 expressed in percent of the total storminess. 



TABLE CVI. 

 Loivcr Limit for Sttn-stonniness. 



The quantity a cannot be entirely due to storms which are not of solar origin. In the first plan it 

 is not impossible that every now and then we also have centres of polar storms on the morning and 

 forenoon side of the earth. At the southern stations Matotchkin-Schar and Kaafjord, forenoon centres of 

 any magnitude are seldom observed; but nearer the magnetic axis and the north pole, at Dyrafjord and still 

 more frequently at Axeloen, centres of fairly small and local polar storms are also found on the fore- 

 noon side. 



In the second place a contains some storminess due to disturbances which do not belong to the polar 

 type, but may still be of solar origin. In our opinion the equatorial storms as well as the cyclo-median 

 perturbations are effects of the same solar agency as that producing the polar storms; but at the polar 

 stations these storms show quite a different diurnal distribution from that of the polar storms. Thus the 

 equatorial storms would produce about equal effects all round the auroral zone, and the cyclo-median 

 perturbation in the instance investigated was strongest on the day side. 



In view of these facts, table CVI shows that at the three southern stations practically all the s/ontif 

 which occurred during the interval of our observations were caused by some agency coining from the .<;;. 



The fact that the lower limit of sun-storminess is smaller for Axeloen than for the other stations, 

 must not lead us to the conclusion that a smaller part of the storminess should be of solar origin at 

 this station. It only means that by the method used we are unable to prove the solar origin of a great 

 part of the storminess at Axeloen. The efficiency of the method depends on the calmness of the station. 

 On account of the character of the distribution of storms on the earth's surface, it is, on the northern 

 hemisphere, merely at stations on the southern border of the auroral zone that we can expect this calm 

 period to be well marked. 



For a place in a lower latitude the storminess will be due mostly to distant systems with their 

 centres near the auroral zone. In the night the disturbed region would be on the same side of the pole 

 as the place considered, while in the day it would be on the opposite side of the pole; but for places 

 far from the poles the difference in the effect of the day and night systems would be diminished, 

 is in accordance with the fact that the great polar storms are accompanied by disturbances in lower 



