PRELIMINARY ANALYSIS OF THE OCCURRENCE FREQUENCY AND △Z/△H OF GEOMAGNETIC STORMS AT BEIJING OBSERVATORY

Changes in the occurrence frequency and AZ/AH of geomagnetic stroms are preliminarily analyzed using 22-year storm data of 1957-1978 at Beijing Observatory in this paper. Statistical results show that 23-00-01-02 h of universal time (UT) are superior hours, and March, April, September, October in a year are superior months for storm occurrence frequency. There is a relation between storm occurrence frequency and solar activity. Changes in the oc-cuirence frequencies of various storms have a periodicity that correlate with the 11-year cycle of solar activity to a certain extent. The change in △Z/△H of SC-type variations has 22-year and 1.4-year periodicities, but the periodicity is not distinct. The change in △Z/△H of the main phase of geomagnetic storms has 22-vear, 11-year, 1.1-year periodicities, and the spectral peak of the 1.1-year period is very noticeable.