BELL SYSTEM TECHNICAL JOURNAL 



(EQ. 



= 2 



1.2 



0.8 I 



0.4 



Fig. 5 — Average daylight and night-time long-\va\-e radio field 

 strength before and after 25 long magnetic storms. 



27-Day Intervals 



Sunspot-numbers and terrestrial magnetic disturbances tend to be 

 repeated at 27-day intervals.^" A recurrence correlation for "radio 

 character" and magnetic character has been published by A. M. 

 Skellett,^^ who based the radio data upon the relative intensity from 

 day to day of the disturbances of the short-wave telephone circuits 

 between New York and London. A recurrence chart for long-wave 

 radio is shown in Fig. 6, based upon the deviation from the 50-day 

 moving average of the average daylight radio field strength of WNL 

 (60 kc.) at Cupar for seven years beginning with March 1927. A 

 measure of the international magnetic character figure ("C") for each 

 day in the same period is likewise shown in this figure. 



It is evident that the 27-day recurrence phenomenon is obscured on 

 long waves, probably because magnetic storms are followed by 

 prolonged effects on the long-wave fields, as was pointed out in con-" 

 nection with Fig. 5. 



Correlation by Days 



The average daylight field strength on long waves is improved on 

 days t)f magnetic disturbance,^* as compared with calm days.'^ Cumu- 

 lative distribution curves of daily averages of daylight field strength of 

 WNL (Rocky Point to Cupar, Scotland) for 1930 and 1933 are shown in 

 Fig. 7, for calm and disturbed days.* Similar data for east-to-west 



* A magnetically calm day is defined for the purposes of this paper as a day for 

 which the international magnetic character figure "C" is from 0.0 to 0.3. A mag- 

 netically disturbed day is here characterized by a figure from L2 to 2.0. 



