Infrared processes in the auroral zone

Abstract

Recently auroral observations have indicated the strong enhancement of certain infrared bands during periods of auroral activity. A theoretical model has been created in order to study the infrared processes associated with the aurora. The quantitative results of this study depend upon a thorough knowledge of the rates of all processes involved. Some of the rate constants are well known, whereas for others we have made only the crudest approximation. Qualitatively, however, our results indicate that certain infrared bands of CO2, N2O, NO, and NO+ are strongly enhanced during periods of auroral activity. This enhancement is primarily the result of two basic energy exchange mechanisms. The energy deposited by the primary auroral electron flux goes into increasing the internal energy of N2, O2, and O. That is, the vibrational temperature of N2 is significantly increased in an aurorally disturbed atmosphere. This energy is then transferred to various infrared active minor constituents such as CO2, N2O, NO, etc. through near-resonant vibrational-vibrational exchange processes, increasing the higher-level Vibrational populations of these species and thereby enhancing their infrared radiative output. In addition to energetic auroral particles as an energy source we have also considered electric fields. Qualitatively the results are similar except that the energy tends to be deposited at altitudes somewhat higher than those in direct precipitation processes.