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| Titel |
Kristian Birkeland's pioneering investigations of geomagnetic disturbances |
| VerfasserIn |
A. Egeland, W. J. Burke |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-5010
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| Digitales Dokument |
URL |
| Erschienen |
In: History of Geo- and Space Sciences ; 1, no. 1 ; Nr. 1, no. 1 (2010-04-12), S.13-24 |
| Datensatznummer |
250000126
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| Publikation (Nr.) |
 copernicus.org/hgss-1-13-2010.pdf |
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| Zusammenfassung |
More than 100 years ago Kristian Birkeland (1967–1917) addressed questions
that had vexed scientists for centuries. Why do auroras appear overhead
while the Earth's magnetic field is disturbed? Are magnetic storms on Earth
related to disturbances on the Sun? To answer these questions Birkeland
devised terrella simulations, led coordinated campaigns in the Arctic
wilderness, and then interpreted his results in the light of Maxwell's
synthesis of laws governing electricity and magnetism. After analyzing
thousands of magnetograms, he divided disturbances into 3 categories:
1. Polar elementary storms are auroral-latitude disturbances now called substorms.
2. Equatorial perturbations correspond to initial and main phases of magnetic storms.
3. Cyclo-median perturbations reflect enhanced solar-quiet currents on the dayside.
He published the first two-cell pattern of electric currents in Earth's
upper atmosphere, nearly 30 years before the ionosphere was identified as a
separate entity. Birkeland's most enduring contribution toward understanding
geomagnetic disturbances flowed from his recognition that field-aligned
currents must connect the upper atmosphere with generators in distant space.
The existence of field-aligned currents was vigorously debated among
scientists for more than 50 years. Birkeland's conjecture profoundly affects
present-day understanding of auroral phenomena and global electrodynamics.
In 1896, four years after Lord Kelvin rejected suggestions that matter
passes between the Sun and Earth, and two years before the electron was
discovered, Birkeland proposed current carriers are "electric corpuscles
from the Sun" and "the auroras are formed by corpuscular rays drawn in
from space, and coming from the Sun". It can be reasonably argued that the
year 1896 marks the founding of space plasma physics. Many of Birkeland's
insights were rooted in observations made during his terrella experiments,
the first attempts to simulate cosmic phenomena within a laboratory.
Birkeland's ideas were often misinterpreted or dismissed, but were verified
when technology advances allowed instrumented spacecraft to fly in space
above the ionosphere. |
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