Hydroxyl airglow observations for investigating atmospheric dynamics: Results and challenges

Abstract

Measurements of hydroxyl (OH∗) airglow intensity are a straightforward and cost-efficient method which allows the derivation of information about the climate and dynamics of the upper mesosphere/lower thermosphere (UMLT) on different spatiotemporal scales during darkness. Today, instrument components can be bought "off-the-shelf"and developments in detector technology allows operation without cooling, or at least without liquid nitrogen cooling, which is difficult to automate. This makes instruments compact and suitable for automated operation. Here, we briefly summarize why an OH∗ airglow layer exists, how atmospheric dynamics influence it and how temperature can be derived from OH∗ airglow measurements. Then, we provide an overview of the scientific results regarding atmospheric dynamics (mainly gravity waves (GWs) but also planetary waves (PWs) and infrasound) achieved with OH∗ airglow measurements. We focus on long-term ground-based OH∗ airglow measurements or airglow measurements using a network of ground-based instruments. The paper includes further results from global or near-global satellite-based OH∗ airglow measurements, which are of special importance for characterizing the OH∗ airglow layer. Additionally, the results from the very few available airborne case studies using OH∗ airglow instruments are summarized. Scientific and technical challenges for the next few years are described.