The Aurora Borealis is an electrical discharge powered by the solar wind and Earth's magnetosphere. The solar wind, a high speed cloud of charged particles streaming out from the Sun's corona, is an enormous river of particles that flows around Earth much like a stream that flows around a rock. The Earth's lines of magnetism stream out too, in a tail, capturing billions of solar particles as they flow by.
The current theory is that when this enormous tail is stretched to its fullest, it snaps back with a surge of power of up to 1,000 billion watts. This burst of magnetic and solar energy excites the atoms and molecules in earth's upper atmosphere where nitrogen and oxygen light up like neon lights, pulsing and glowing in the sky at heights of 80 to 1,000 kilometres above the earth.
Powerful surges of solar wind can cause disruptions of radio communications and navigational difficulties. Satellite performance can be affected and variations in the ionosphere can induce electric currents in power lines, telegraph wires and pipelines, causing transformer malfunction, power outages and other damage.
The 11-year cycle of the sun has a significant influence on the frequency and intensity of the northern lights. The years 2011 to 2013 are expected to be peak years.
A substorm is another name for an intense auroral display. There are an estimated 1500 substorms causing dramatic displays each year. Sometimes several can be seen in a night – sometimes there are several days between major substorms.