The concept of magnetic reconnection for the interaction of the solar wind plasma with the Earth's magnetosphere is illustrated by Dungey's [1961] classic drawing (Figure 1a). According to this concept, the interplanetary magnetic field (IMF) lines, frozen in to the antisunward solar wind plasma flow, divide, or disconnect, at an X-line at the magnetopause, with one end going over the north pole and the other end over the south pole. The polar cap field lines are called “open,” with only one end connected to the Earth; the total amount of open flux over the two polar caps must be the same to conform to Maxwell's equations.