Abstract
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)
Highlights
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
Kockarts dealing with atmospheric regions where photodissociation and ionization processes play a role. It was officially introduced during the 1954 General Assembly of the International Union of Geodesy and Geophysics (IUGG) in Rome
During this assembly the International Association of Magnetism and Electricity changed its name to become the International Association of Geomagnetism and Aeronomy. This official recognition of the term does not imply that no researchers were involved in aeronomy before that time
Summary
The word “Aeronomy” has been coined by the great geophysicist Sidney Chapman. It can be defined as the science. As noted by Jeans (1925), all these calculations assume that the terrestrial atmosphere is composed of two layers, one with an adiabatic regime up to approximately 11 km at mid-latitude and one with a constant temperature above that height This was a consequence of observations available at that time. Wegener (1911) even introduced a hypothetical monoatomic constituent, called geo-coronium with a mass of 0.4 amu, in order to explain an unknown line in the auroral spectrum This hypothesis was refuted by Chapman and Milne (1920), since the existence of such super light constituent would imply an escape flux so high that the constituent should disappear from the atmosphere. Up to 20 km constituents are in perfect mixing and above that height molecular diffusion leads to a separation
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