Secular and Solar Cycle Variations of Geomagnetic Storm Occurrences at Kakioka
Sano, Y. & Saito, T.
Abstract
Various occurrence features of geomagnetic storms during the period from 1924 to 1982 at Kakioka have been investigated in detail relating to sunspot activity. The present study aims mainly to clarify solar cycle and/or heliomagnetic polarity dependences of the storm occurrence frequency. Of course, their secular variation are also a very interesting subject. Main results are as follows;
(1) Annual sc-storm occurrence frequency as a function of the sunspot number has such a heliomagnetic polarity asymmetry as the larger (smaller) storms occur more frequently in the S (N) polarity epoch of the heliomagnetic field. In particular the huge storms (sc-amplitude> 100 nT or storm range>500 nT) occur only in the S polarity epoch.
(2) Annual sc-storm occurrence frequency has a good correlation with the sunspot number as high as 0.9, except in the present 21st solar cycle.
(3) Sg-storm occurrence frequency has a major and a minor maximum in the late decreasing and in the increasing phase of the solar cycle, respectively, and shows about one-year difference in the maximum occurrence year between the two heliomagnetic polarity epochs.
(4) Maximum sg-storm occurrence frequency in each solar cycle shows in general such a secular variation (long-term trend) as it changes nearly proportionally to that of the sunspot number, but it is relatively large in the 18th solar cycle and extremely small in the 19th solar cycle.
(5) Sc* occurrence frequency and its occurrence rate against sc's suddenly increased in 1956, and thereafter both have maintained higher values than before on the average.
