Recurrence tendency of geomagnetic activity during the current sunspot minimum

Abstract

Geomagnetic Activity during the three year period June 1950-June 1953, has been analysed and found to consist mainly of two very long sequences of recurrent (27-day period) moderate geomagnetic storms. During the three year period there have been 40 recurrences of one of these sequences (called the A sequence) and 2I recurrences of the other sequence (called the B-sequence). Moreover these sequences have continued beyond the period studied. Each sequence exhibits a periodic variation in its activity with a period of one yea). For the A-sequence the maxima lie near September and minima near March; whereas for the B-sequence the maxima lie near March and minima near September. The explanation of this variation is found to lie in the tilt of the solar axis of rotation to the ecliptic; the heliographic latitude of the earth attains its maximum positive and negative values on 7 September and 5 March respectively. The M-region responsible for these long sequences are located above 7°'2 heliographic latitude and separated by about 1300 in longitude. The M-region associated with the A-sequence ties in the northern hemisphere and the other one in the southern hemisphere.