History
After Kristian Birkeland first suggested in 1908 that "currents there are imagined as having come into existence mainly as a secondary effect of the electric corpuscles from the sun drawn in out of space," the story appears to have become mired in politics. Birkeland's ideas were generally ignored in favor of an alternative theory from British mathematician Sydney Chapman.
- In 1939, the Swedish Engineer and plasma physicist Hannes Alfvén promoted Birkeland's ideas in a paper published on the generation of the current from the Solar Wind. In 1964 one of Alfvén's colleagues, Rolf Boström, also used field-aligned currents in a new model of auroral electrojets.
- Proof of Birkeland's theory of the aurora only came after a probe was sent into space. The crucial results were obtained from U.S. Navy satellite 1963-38C, launched in 1963 and carrying a magnetometer above the ionosphere.
- In 1966 Alfred Zmuda, J.H. Martin, and F.T.Heuring analysed the satellite magnetometer results and reported their findings of magnetic disturbance in the aurora, but did not mention Alfvén, Birkeland, or field-aligned currents, even after it was brought to their attention by the editor of the space physics section of the journal, Alex Dessler.
- In 1967 Alex Dessler and one of his graduates students, David Cummings, wrote an article arguing that Zmuda et al. had indeed detected field-aligned currents. Alfvén subsequently acknowledged that Dessler had "discovered the currents that Birkeland had predicted" and they should be called Birkeland-Dessler currents. 1967 is therefore taken as the date when Birkeland's theory was finally acknowledged to have been vindicated.
- In 1969 Milo Schield, Alex Dessler and John Freeman used the name "Birkeland currents" for the first time.
- In 1970 Zmuda, Armstrong and Heuring wrote another paper agreeing that their observations were compatible with field-aligned currents as suggested by Cummings and Dessler, and by Boström, but again made no mention of Alfvén and Birkeland.
- Also in 1970 a group from Rice University also reported that the results of an earlier rocket experiment was consistent with field-aligned currents, and credited the idea to Boström, Dessler and his colleagues, rather than Alfvén and Birkeland. In the same year, Zmuda and Armstrong did credit Alfvén and Birkeland, but felt that they "cannot definitely identify the particles constituting the field-aligned currents but ... the current is probably carried by electrons".
- In 1973 the US Navy satellite Triad, carrying equipment from A. Zmuda and James Armstrong, detected the magnetic signatures of two large sheets of electric current. Armstrong and Zmuda's papers in 1973 and 1974 reported "more conclusive evidence" of field-aligned currents, citing Cummings and Dessler but again not mentioning Birkeland or Alfvén.
Read more about this topic: Birkeland Current
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