Magnetic Field of Lines

The process of magnetic field lines is also essential to the aurora. It is already mentioned large electric currents flowing from the tail into the polar regions and back again, flowing along magnetic field lines, earthward on the morning side of midnight, outbound on the evening side (for the main circuit--a secondary one also exists).

They were first mapped in 1973 by two US scientists, Al Zmuda and Jim Williamson--not with a well-supported space research mission, but using a small experiment and a bummed "piggy-back" ride with a navigational satellite of the US Navy. Those currents are now known as "Birkeland currents," honouring the Norwegian who first shot electron beams at a magnet in vacuum.

The spectacular aurora borealis displays that light up the northern nights could be powered by a gigantic "slinky" effect in Earth’s magnetic field lines. Earth’s magnetic field resemble a slinky in that when "wiggled," it undulates in waves that travel down the field lines at speeds up to 25 million miles per hour. These waves can pass energy to electrons, accelerating them along the magnetic field lines toward Earth. When the electrons hit atoms in the atmosphere, the atoms become excited and produce the colours of the aurora. Waves in the magnetic field lines are called Alfven waves, after Hannes Alfven, a Swedish physicist who helped found the field of plasma physics, said Wygant.
For many years the identity of the primary particles producing the aurora was uncertain, although laboratory experience suggested that they behaved like cathode rays, i.e. electrons. Harang [1951, p. 140] wrote:
"It has been commonly assumed that the electrically charged particles producing the aurorae are cathode-rays, although no definite proof of this hypothesis can be given. The possibility of positive rays, a rays or protons being the primary cause of aurorae cannot be excluded."


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