Aeronomy, a 20th Century emergent science: the role of solar Lyman series

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 guideline 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.

Remote sensing planetary waves in the midlatitude mesosphere using low frequency transmitter signals

“…Reasons for reduced electron density during periods of increased neutral density in the height range in question are: less ionization because of larger opacity and increased recombination rates. With respect to increasing opacity we note that the ionization rate of the most relevant ionizing process in the D-layer, NO-ionization by solar Lyman α radiation, drops exponentially with increasing total content of molecular oxygen along a fixed vertical line of sight (Kockarts, 2002). Figure 9 illustrates model calculations for two rather extreme situations as with 27 November and 2 December 2010 (cp.…”

“…The collision frequencies (s −1 ) used in our model have been taken from Kelley (2009): ν in = 2.6 × 10 −9 n n A −1/2 for the ion-neutral collision frequency, ν e = 5.4 × 10 −10 n n T 1/2 e + (34 + 4.18ln(T 3 e /n e )) n e T −3/2 e for the sum of the electron-neutral and electron-ion collision frequency. n n , n e are the neutral and electron densities per cubic centimeter, A is the mean neutral molecular mass and T e the electron temperature in Kelvin.…”

Lyman α airglow emission: Implications for atomic hydrogen geocorona variability with solar cycle

“…Empirical quantification of the atomic hydrogen density distribution, [H( z )], in the terrestrial upper atmosphere remains sparse, despite its importance for accurate photochemical modeling, for assessing atmospheric evolution via planetary escape, and for supporting magnetospheric imaging capabilities. Atomic H is produced in the middle atmosphere, mainly through photodissociation of hydrogenous molecular species of tropospheric origin, including anthropogenic methane [ Kockarts , ], and its photochemically initiated vertical flux, φ , governs its abundance and transport throughout the thermosphere [ Bishop , ]. Above its peak density in the mesosphere/lower thermosphere (MLT) near 90 km, its direct production is balanced by upward diffusion, leading to an estimated global mean escape flux of a few 10 8 cm −2 s −1 .…”

Responses of the ionospheric D-region to periodic and transient variations of the ionizing solar Lyα radiation

“…As numerous studies have shown, all these parameters are variable in space and time and they can be calculated from experimental data obtained by various observational techniques. Thus, variations in the Lyα irradiance during solar cycles and seasons are presented in Woods et al (2000), Fröhlich (2009) and Correia, Kaufmann, Raulin, Bertoni, and Gavilan (2011) and results given in Kockarts (2002) exhibit a strong zenith angle dependency of Lyα line absorption coefficients in the atmosphere. Also, measurements of the NO density show values within a wide range at fixed altitudes (Aikin, Kane, & Troim, 1964;Pearce, 1969;Barabash, Osepian, Dalin, & Kirkwood, 2012; and references therein).…”