A plot of the Dst index since 1957 from the World Data Center, Kyoto (http://wdc.kugi.kyoto-u.ac.jp/dstdir/). The vertical streaks extending beyond −100 nT are the major storms. The largest storm (Dst approximately −589 nT) is the one on 13 March 1989 storm, which caused the power blackout in Quebec, Canada (Allen et al. 1989). The Halloween 2003 storm was the next largest storm (Dst < −400 nT) after the Quebec storm (Mannucci et al. 2005). The positive excursions are the sudden commencements or sudden impulses caused by the impact of CME-driven shocks on the magnetosphere. The sunspot number is plotted at the bottom for reference.