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Ann. Geophys., 20, 585-598, 2002
www.ann-geophys.net/20/585/2002/
© European Geosciences Union 2002
Aeronomy, a 20th Century emergent science: the role of solar Lyman series
G. Kockarts
Institut d’Aéronomie spatiale de Belgique, 3 avenue Circulaire, B-1180 Brussels, Belgium
Correspondence to: G. Kockarts (gaston.kockarts@oma.be)
Abstract. Aeronomy is, by
definition, a multidisciplinary science which can be used to study the
terrestrial atmosphere, as well as any planetary atmosphere and even the
interplanetary space. It was officially recognized in 1954 by the International
Union of Geodesy and Geophysics. The major objective of the present paper is to
show how aeronomy developed since its infancy. The subject is so large that a
guide-line has been chosen to see how aeronomy affects our atmospheric
knowledge. This guideline is the solar Lyman alpha radiation which has
different effects in the solar system. After a short description of the origins
of aeronomy the first observations of this line are summarized since the
beginning of the space age. Then the consequences of these observations are
analyzed for the physics and chemistry of the neutral terrestrial atmosphere.
New chemical processes had to be introduced, as well as new transport
phenomena. Solar Lyman alpha also influences the structure of the Earth’s
ionosphere, particularly the D-region. In the terrestrial exosphere, solar
Lyman alpha scattered resonantly by atomic hydrogen is at present the only way
to estimate this constituent in an almost collisionless medium. Since planetary
atmospheres also contain atomic hydrogen, the Lyman alpha line has been used to
deduce the abundance of this constituent. The same is true for the
interplanetary space where Lyman alpha observations can be a good tool to
determine the concentration. The last section of the paper presents a question
which is intended to stimulate further research in aeronomy.
Key words. Atmospheric composition
and structure (middle atmosphere – composition and chemistry; thermosphere
– composition and chemistry) – history of geophysics (atmospheric sciences)
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