Model studies of hydroxyl airglow under the influence of ionization.
Final Report Abstract
Emissions of vibrationally excited hydroxyl molecules (OH*) are useful indicators for dynamical and chemical processes in the Earth’s mesosphere (the altitude region of about 45-90 km). The response of OH* to sporadic ionization events provides an interesting opportunity to test our understanding of the mesosphere under perturbed conditions. However, so far the observed OH* emissions during ionization events are hardly investigated. The aim of this project was to investigate the effects of ionization on OH* in the mesosphere. For this purpose, existing ion and plasma chemistry models have been improved. There is an ion chemistry model which accounts for chemical reactions, quenching as well as emission of OH*. This model is suitable to simulate the impact of ionization due to precipitating energetic charged particles of solar origin. In order to simulate the impact of electric discharges above thunderstorm clouds, a more complex plasma chemistry model is needed. In particular, this model has to additionally simulate energy exchange reactions between excited molecules and atoms. The ion chemistry model was applied to the major solar particle event of October-November 2003 in the northern polar region. It was found that the measured OH* perturbations are due to an interplay of dynamical and chemical changes. In particular, only if temperature changes are taken into account, the model is able to reproduce the measured OH* emissions. The main effect is caused by temperature-dependent chemical reaction rates. The ion chemical processes are of minor importance. The plasma chemistry model was used to simulate the processes in the plasma filaments of so-called sprite discharges occurring above active thunderstorm clouds. The model predicts a characteristic pattern of the excitation of the different T-vibrational states of OH*. Immediately after the electric discharge, the concentrations of all vibrational states are significantly increased. After a few seconds, however, there is a rapid decrease of the high vibrational excitations. This is mainly due to different production reactions of the low and high vibrational states of OH*, and effective quenching reactions. The modeled OH* concentrations are highest in the middle mesosphere, and are therefore a possible source of the unexplained emissions detected during electric breakdown events in this altitude region. A comparison of modeled and observed emissions is planned for the future.
Publications
- Hydroxyl emission altitude variability during the last solar cycle retrieved from SCIAMACHY nightglow observations, EGU General Assembly, 2015
G. Teiser, C. von Savigny, and Holger Winkler
- Effect of the solar proton events on the OH Meinel emission altitude and variability in Hydroxyl airglow during the last solar cycle retrieved from SCIAMACHY nightglow observations, DPG Regensburg, 2016
G. Teiser, C. von Savigny, H. Winkler
- Modelling the effects of solar particle events on vibrationally excited hydroxyl, EGU General Assembly, Vienna, 2016
H. Winkler, J. M. Wissing, G. Teiser, C. von S., and J. Notholt
