When the supersonic solar wind hits the Earth's magnetic field, a powerful electrical connection occurs with Earth's field, generating millions of amperes of current that drive the dazzling auroras. These so-called Birkeland currents connect the ionosphere to the magnetosphere and channel solar wind energy to Earth's uppermost atmosphere. Solar storms release torrential blasts of solar wind that cause much stronger currents and can overload power grids and disrupt communications and navigation.