136 



BIRKELAND. THE NORWEGIAN AURORA POLARIS EXPEDITION, 1902 1903. 

 Current-Arrows for the 22nd March, 1903; Chart VII at 23 h . 



Fig. 60. 



The current-arrows indicate very decidedly two current-vortices, a positive vortex in the north 01 

 North America, and a negative one about the river Obi in Siberia, answering respectively to areas of 

 divergence and convergence of the perturbing forces. 



As we have no observations from places near the points of convergence, we cannot here recognise 

 the characteristic perpendicular position of the total force in relation to the earth's surface. 



As regards the cause, we may confine ourselves to referring to the previously-described elementary 

 storms. Here too it is difficult to understand how the perturbation in lower latitudes can be mainly due to 

 plane currents, as in that case this peculiarly formed current-system should retain its form and position 

 for nearly 2 ! /2 hours. 



The slight oscillation of the force in Europe on this date, is in accordance with the fact that the 

 point of convergence is now far to the east, and this is certainly connected with the circumstance that 

 the perturbation appears so early in the night, reckoning by Greenwich time. At the Norwegian stations 

 about the auroral zone, the current-arrows point in the characteristic direction westwards along the zone. 

 On this date the vertical components at Bossekop and Axeleen are exceedingly powerful and in opposite 

 directions, answering to a current passing between the two stations. At Dyrafjord, P, is comparatively 

 smaller, indicating that the current should pass north of this station. 



We have no observations for this date from Matotchkin Schar. From Potsdam no curves for V 

 were received. For Ekaterinburg nothing can be taken out. 



