Photo: Cartoon sketch of how tangled magnetic fields can cause a flare. Inset shows a SOHO/EIT image of the July 14th, 2000 flare on the Sun.
When electrical circuits get crossed, you often see sparks fly and lots of smoke as the wires become heated. The electricity, carried by electrons in one wire are trying to flow one way, while the electrons from another circuit are trying to flow the opposite way in the same material. This causes the electrons to collide, and instead of an organized smooth flow, it becomes disorganized. The energy of motion (kinetic energy) of the electrons in the currents is transformed into heat energy as nearby atoms in the wire are jostled about. A very similar thing happens on the Sun, but with dramatic consequences that extend clear across the entire solar system!
Scientists can learn a great deal about how the currents and magnetism on the Sun work as a system by studying models of the Sun's surface in their laboratories or in detailed computer calculations. Even though the difference in size between the Sun (6.5 x 1010 meters) and a lap top computer ( 0.3 meters) is enormous (about 2x 1011 times), many physical laws can be scaled up or down in size so that even enormous solar flares can be investigated in human-sized models. Sometimes one group of sunspots collides with another like ships floating on the Sun's plasma ocean. Sometimes a brand new sunspot can appear inside one that was already there. If the polarities are the same, nothing much happens. But if they are opposite each other in some area of the Sun's surface, then this can only mean one thing. There must be currents of flowing gas that are moving in opposite directions within the same piece of the Sun's surface.
Because sunspots and the gases around them can flow at thousands of miles a minute, it only takes a few minutes before magnetic conditions can escalate from a minor solar squall to a major explosion of energy. The billions of amperes of current moving in opposite directions through the solar atmosphere release over 1015 (1000 trillion) Joules of energy; more energy than in a thousand hydrogen bombs. Within 20 minutes, the magnetic field reconnects into a smoother shape to release the energy, but meanwhile, gas has been heated to millions of degrees and a blast of x-rays and other energetic particles leaves the scene of the event. In 9 minutes, the x-rays traveling at 3 x 105 kilometers/second arrive at the Earth located 1.5 x 108 kilometers from the Sun, and cause short-wave blackouts across the entire daytime face of the planet. An hour or so later, a burst of slower-moving, but enormously energetic particles flows by the Earth. Any astronauts in space, or sensitive satellites, will be bombarded by these particles and may suffer lethal doses of radiation.
The Sun can be active in other ways as well, and these can be just as troublesome for humans and their technology.
2000... TRACE discovers that solar flares are a significant source of heating the solar chromosphere and corona.
2000... TRACE discovers complex gas flows and filaments in solar flares.
1998...ACE detects heavy ion acceleration in elements from carbon through iron in impulsive solar flares.
How can we relate the size of a solar flare to its impact on Earth?