Annales Geophysicae ISSN: 0992-7689 (printed version) ISSN: 1432-0576 (electronic version) Abstract Volume 14 Issue 3 (1996) pp 286-289
Seasonal variations in the occurrence of geomagnetic storms John R. Taylor, Mark Lester, Timothy K. Yeoman Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK Received: 24 August 1994/Revised: 16 October 1995/Accepted: 23 October 1995 Abstract. Seasonal variations in the onset of magnetic storms are investigated. For the purposes of this study storms have been defined as events in which Dst falls below -50 nT for at least four consecutive hours. The storms have been classified as either storm sudden commencements (SSCs; storms initiated by a sudden commencement) or as storm gradual commencements (SGCs; all other storms). It is found that the semi-annual variation of magnetic activity is reflected in the occurrence statistics of SGC events only, indicative that the solar wind origin is different for SSCs and SGCs. It is suggested that the heliospheric latitude model of seasonal magnetic activity is relatively ineffective in modulating the previously observed seasonal variations in the occurrence of magnetic storms. Article not available online Last change: February 23, 1997
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