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aeronomy(air-on -ŏ-mee) The physics and chemistry of the upper atmosphere of the Earth, i.e. its temperature, density, motions, composition, chemical processes, reactions to solar and cosmic radiation, etc. The term has been extended to include the physics and chemistry of the atmospheres of the other planets.
a branch of atmospheric physics in which atmospheric processes are studied from the point of view of atomic and molecular interactions and of the interaction of solar radiation with the atoms and molecules of the air.
Aeronomy became a special branch of atmospheric physics in the 1950’s. Its founders were D. R. Bates (England) and M. Nicolet (France); they were concerned mainly with the upper atmosphere. Rapid development in aeronomy is connected with progress in rocket and satellite research which made possible direct study of the physicochemical processes of the upper atmosphere. The range of problems studied in aeronomy is constantly widening. The most important ones concern neutral particles, the electron-concentration profile, noctilucent clouds, luminescence of the nocturnal sky and aurora polaris, and radiation belts.
The study and interpretation of the altitude distribution of temperature, density, and composition of neutral particles in the air are closely connected with the compilation of so-called standard atmospheres (special reference guides of atmospheric properties), which have great practical value in the age of satellites and rockets. Rapid rise in temperature with increased altitude in the 90–300 km range has been successfully explained by studying the characteristics of dissociation and ionization of particles in the air by ultraviolet solar radiation, and also by detailed study of the spectrum structure of solar radiation.
Along with the study of chemical reactions, research on the composition of air in the upper atmosphere requires calculation of diffusion and thermodiffusion processes, which carry the products of chemical reactions from their zone of origin to the neighboring altitude zones. As a result of these processes the distribution of pressure of certain components of air deviates at altitudes under 200 km from that calculated using the barometric formula.
Aeronomy studies and also clarifies the electron-concentration profile (electron concentration as a function of altitude) in the ionosphere. It has been ascertained that the complex sequence of chemical reactions with charged particles permits correct description of change with altitude of electron concentration. However, up to now the problem of calculation of the electron-concentration profile cannot be considered conclusively resolved.
The presence of charged particles in the ionosphere requires consideration of the earth’s magnetic field, since air movement also carries charged particles. Negative charges are deflected in one direction by the earth’s magnetic field, and positive ones in the other. This leads to the development of electric currents in the earth’s ionosphere. Thermodiffusion in a field of abrupt temperature changes with altitude tends to divide heavy ions and light electrons, and this process leads to the appearance of weak electrical fields.
As aeronomy has developed, it also turned to solving problems of lower levels. An example of this is investigation of the ion layer at an altitude of 25–35 km, caused by reemission of cosmic radiation. Study of the 24-hour course of ion concentration in this layer points to the necessity for studying the entire cycle of chemical reactions with charged particles and ozone.
Aeronomy studies noctilucent clouds and has explained in general terms their nature.
Aeronomy has given considerable attention to investigation of processes leading to luminescence of the nocturnal sky and to aurora polaris. For example, an understanding of the nature of 5,577 angstroms’ luminescence of the nocturnal sky has made it possible to invent a method of measuring the total content of atomic oxygen and to observe its variation with time.
Aeronomy also studies the processes leading to formation of the earth’s radiation belts.
This list does not exhaust the entire range of problems in aeronomy, which broadens and changes with each passing year.
REFERENCESKhvostikov, I. A. Fizika ozonosfery i ionosfery. Moscow, 1963.
Danilov, A. D. Khimiia ionosfery. Leningrad, 1967.
Nicolet, M.Aeronomiia. Moscow, 1964. (Translated from English.)
lvanovskii, A. I., A. I. Repnev, and E. G. Shvidkovskii. Kine-ticheskaia teoriia verkhnei atmosfery. Leningrad, 1967.
A. I. IVANOVSKII