U.S. contributions to auroral aeronomy, 1979‐1982

Abstract

Auroral aeronomy is the scientific discipline devoted to the study of the interaction of energetic particles and electric fields with the atmosphere of planets that have an appreciable intrinsic magnetic field. Specific topics that describe this interaction include: transport and energy degradation of energetic electrons and ions in a collision dominated medium, the excitation of atoms and molecules by collisions and by chemical reactions, the auroral spectrum, its production and interpretation, perturbations upon the ionospheric plasma in terms of enhanced ionization, composition, dynamics and heating, and perturbations upon the neutral atmosphere in terms of composition, dynamics and heating.It is not possible, however, to identify aeronomic processes as being uniquely relevant to the aurora because solar EUV photons and photoelectrons are subject to similar physical and chemical reactions leading to spectral emissions that also result from auroral electron bombardment of the atmosphere. Thus, a large segment of aeronomic research carried out during the quadrennium is reviewed in companion articles of this report to the I.U.G.G. An overview of Polar and Auroral Phenomena is presented by Reiff [1983, this issue]. She reviews auroral morphology, including pulsating aurora, emphasizing the relationship to magnetospheric phenomenology. Local and global characteristics of energetic particle precipitation are presented, and a summary of recent observations of energetic ions of ionospheric origin is given. Observations and theories on auroral electrodynamics are also reviewed by Reiff [1983], The effects of heating and ionization on Thermospheric Dynamics are reviewed by Roble [1983, this issue]. Progress in our understanding of the Neutral and Ion Composition of the Thermosphere is reported by Torr [1983, this issue]. This review focuses on reaction rate coefficients that are inferred from rockets and satellite observations of ion and neutral densities and optical emission rates, a technique that is particularly useful for studying metastable states of atmospheric gases. The chemical–ionic reactions pertinent to the dayglow are also relevant to the aurora so that progress in auroral aeronomy leans heavily on our understanding of the aeronomy at middle and low latitudes . Dynamical effects of auroral electric fields upon the high latitude ionosphere are discussed in the review by Richmond [1983, this issue]. The aurora and, in particular, the energetic solar proton events (SPE) significantly perturb the middle atmosphere, i.e. the mesosphere and upper stratosphere. Effects upon the chemistry and ionization are reviewed by Solomon [1983, this issue] while the dynamic and electrodynamic consequences are discussed, respectively, by Hartmann [1983, this issue] and by Kelly [1983, this issue].