Solar wind drivers of geomagnetic storms during more than four solar cycles

• Published in: Journal of space weather and space climate Vol. 2; p. A01
• Main Authors: Richardson, Ian G., Cane, Hilary V.
• Format: Journal Article
• Language: English
• Published: les Ulis EDP Sciences 01.01.2012
• Subjects: Automation; Classification; Coronal holes; Coronal mass ejection; Geomagnetic storms; Geomagnetism; Interplanetary Coronal Mass Ejection (CME); KP index; Low level; Magnetic fields; Magnetic storms; NOAA; Solar corona; Solar cycle; Solar cycles; Solar wind; Space weather; Storm; Storms; Stream; Sun
• ISSN: 2115-7251; 2115-7251
• DOI: 10.1051/swsc/2012001

Using a classification of the near-Earth solar wind into three basic flow types: (1) High-speed streams associated with coronal holes at the Sun; (2) Slow, interstream solar wind; and (3) Transient flows originating with coronal mass ejections (CMEs) at the Sun, including interplanetary CMEs and the associated upstream shocks and post-shock regions, we determine the drivers of geomagnetic storms of various size ranges based on the Kp index and the NOAA “G” criteria since 1964, close to the beginning of the space era, to 2011, encompassing more than four solar cycles (20–23). We also briefly discuss the occurrence of storms since the beginning of the Kp index in 1932, in the minimum before cycle 17. We note that the extended low level of storm activity during the minimum following cycle 23 is without precedent in this 80-year interval. Furthermore, the “typical” numbers of storm days/cycle quoted in the standard NOAA G storm table appear to be significantly higher than those obtained from our analysis, except for the strongest (G5) storms, suggesting that they should be revised downward.