Alfvén waves

Alfvén waves are magnetohydrodynamic waves that appear in a plasma (i.e. an ionised gas at high temperature) immersed in a magnetic field. These waves take the form of field oscillations, locally driving ion oscillation. It is these oscillations that travel and not the ions (like the compression in a sound wave).

They were described theoretically by the Swedish physicist Hannes Alfvén (Nobel physics prize, 1970), and were found in 2007 in the solar corona, providing an explanation of its high temperatures. Alfvén waves travel at very high speed, reaching several thousand kilometres per second.