PART II. POLAR MAGNETIC PHENOMENA AND TERRELI.A EXPERIMENTS. CHAP. III. 543 



southern stations, the N storminess in vertical intensity showing only ow well-defined maximum at 

 midnight local time. 



The negative storminess in H, however, shows two instead of one maximum. There is one maximum 

 four hours before midnight, and one four hours after midnight. The occurrence of these maxima is not 

 accidental, but they are repeatedly found for each monthly period (see figs. 193 and 194). 



It is to be expected that the effects of storms with their centres chiefly in the maximum zone of 

 aurora would be felt during a longer time-interval of the day at a station situated nearer the pole. This 

 will be evident from the fact that a place near the pole and magnetic axis will have about the same distance 

 to the centre of the average storm at any hour of the day. Consequently we should expect for Axeloen 

 to get a broadening out of the maxima. But we cannot in this way explain the occurrence of the two 

 distinct maxima at Axeloen ; for at the time they occur, we have no corresponding maxima at Kaafjord, 

 which is just on the opposite side of the auroral zone and situated almost on the same meridian. The 

 two maxima of SJJ for Axeloen must therefore be caused by systems of a very local nature, in other words 

 by electric currents near the station. The effect of those systems dies away so suddenly towards the 

 south, that even at Kaafjord their effect is inappreciable. 



Remembering that the auroral zone passes between Axeleen and Kaafjord and nearest to the latter 

 station, we conclude that these local current-systems occur at a considerable distance to the north of this 

 /.one, and much farther north than the somewhat great midnight storms, which have their centres usually 

 midway between the two stations. 



We see that also through the study of the diurnal distribution of storminess we are led to assume 

 the existence of local storms wif/i their centres to the north of the auroral zone. 



These centres of local storms occurring in the vicinity of the poles, show quite another diurnal 

 distribution than the greater storms in lower latitudes. At Axeloen they are strongest and most frequent 

 at eight o'clock in the evening and four o'clock in the morning; but small local disturbances are here 

 frequently found also during the day-time. 



Thus we come to the following conclusion : The great storminess and the very small calmness of 

 Axeloen compared with the other stations is chiefly due to local disturbances with their centres nearer 

 the poles, and showing another diurnal distribution than the greater and usually more universal storms, 

 which have their centres in the auroral zone. 



To judge from the direction of the horizontal component of the perturbing force, these small 

 disturbances should belong to the type of negative storms, because the current-arrows are turned towards 

 the west. 1 think, however, it will be best to restrict the class of negative polar storms to those which 

 have their centres near the auroral zone; for it is evident that it is only at some distance from the pole 

 that we may expect to find distinct types of positive and negative storms. 



Further, when we compare the storminess in the vertical direction, the similarity between the negative 

 storms and these northerly local storms will be difficult to maintain. 



Comparing the curves of storminess for Axeloen we find for Sy no sign of maxima corresponding 

 to the two distinct maxima of S",. Thus the local centres near tin's station produce practically no 

 disturbance in the vertical direction, 



The simplest explanation of this fact is that the station is placed near a horizontal current-sheet, 

 in other words that the currents producing the local disturbances extend over an area, which has great 

 dimensions compared with the smallest distance between the station and the current-sheet. 



The storminess S r at Axeloen follows exactly the same diurnal distribution as that shown by the 

 storminess at Kaafjord, which indicates that the storminess Sr for Axeloen is mainly due to the positive 

 and negative storms passing between the two stations, and which we found to be caused by currents 

 mostly restricted to a comparatively small cross-section. 



