It is what you get out of the plugs in your home, the current used for the light bulb, the television and nearly all other electrical equipment that we use in our everyday live! Don't ever touch a live plug or wire though, or you could kill yourself.
In the plugs the current is oscillating with a fixed frequency (50 Hz) and this is not what happens on the sun. AC currents on the sun are more easily explained with the help of a long string. If you swing one end of the string the disturbance you generate propagates along the string as a single pulse. The important difference between the string and the solar magnetic field is that the magnetic field is not just one single string, is lots of field lines filling all of space. Therefore if one fieldline is perturbed by being shaken the effects spread to the neighbouring fieldlines. It is somewhat like dropping a stone into a puddle of water, where a circular wave spreads out from the centre of the impact. When more than one stone is dropped at the same time several waves appear and they move through each other. At the locations where two waves are in contact the wave amplitude can either grow, diminish or even completely disappear.
We needed to find ways that the energy in the wave can be released in the corona. There are two possible known ways that this may happen, namely phase mixing and resonant absorption.
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