The Sun goes through an eleven-year cycle of high and low activity that affects space weather and Earth. During times of high activity, the number of sunspots, coronal holes, and solar flares increases. The solar wind — the constant stream of protons and electrons flowing from the Sun — also varies in strength according to the Sun's activity. Events such as coronal holes and solar flares increase the outflow of charged particles from the Sun. Thus at times of high solar activity, the solar wind is stronger and carries a greater number of protons and electrons ejected from the Sun.
The solar wind carries this stream of charged particles through the solar system, dragging the interplanetary magnetic field (IMF) with it. The IMF is the magnetic field produced by the Sun, similar to Earth's magnetosphere. Typically, the magnetosphere surrounds and protects the Earth by deflecting most of the solar wind. However, when the IMF interacts with the magnetosphere, some solar particles are able to leak in along the magnetic field lines at the North and South Poles, affecting Earth's atmosphere and causing auroras.
Also common during periods of high solar activity are coronal mass ejections (CME), which can eject enormous amounts of solar material — up to a few billion tons of plasma — towards Earth. Traveling at a few million miles per hour, a CME typically takes three or four days to reach Earth. When it finally arrives, the gush of material and energy warps and distorts Earth's magnetic field. The result is a geomagnetic storm — a disturbance in the magnetosphere that can disrupt radio communications and navigation systems and can also be hazardous to satellites, electrical equipment, and pipelines.
A good example of the damage that a CME can cause is the 1989 blackout in Canada, when a disruption in the magnetosphere shut down the power to the entire province of Quebec. Because fluctuations of a magnetic field can induce current, the disruptions in Earth's magnetic field caused by a CME are able to induce additional electrical current within the grids of a power system, wreaking havoc by overloading transformers and tripping circuit breakers. Similarly, a current can be induced into other long conductive materials, such as pipelines, and accelerate the rate of corrosion.