On geomagnetic sudden commencements, sudden impulses, and storm durations

Abstract

After a study of the morphology of geomagnetic sudden commencements during the IGY, their accompanying phenomena, such as sudden increases of cosmic noise absorption, bursts of bremsstrahlung X rays, and commencements of geomagnetic micropulsations, are examined. Geomagnetic sudden impulses observed during the IGY are then studied similarly. Four types are found, three of which are completely analogous, both in their morphologies and in their accompanying phenomena, to the coresponding types of sudden commencements. The average duration of the storm depression of the horizontal geomagnetic field, usually attributed to the ring current, is also studied. Storms during years of great solar activity are found to be about three times longer than those during years of little solar activity. The spectrum of storm durations is found; it is concluded that even sudden impulses belong to the family of storms. Possible causes of all these related phenomena, including increases of cosmic noise absorption and micropulsations, are discussed.