Observations of the OH Airglow at the UFS Schneefernerhaus: 1) long-term development and 2) atmospheric waves related to the Hunga Tonga-Hunga Hapaai eruption

Kurzfassung

Observations of OH airglow provide an important opportunity for tracing the variability of the mesosphere lower thermosphere (MLT, ~80-100 km height) on time scales from minutes to decades. While OH rotational temperatures are derived on a routine basis, precise absolute radiances of OH airglow are usually only available from satellite missions or astronomical sites. In order to provide traceability also to the ground-based Network for the Detection of Mesosphere Change (NDMC) a new calibration approach was developed and applied to observations performed at Environmental Research Station (UFS) Schneefernerhaus (11.0°E, 47.0° N). On time scales of decades, the correlation of OH temperatures and OH radiances with solar activity (i.e. with F10.7cm) at UFS is particularly striking. Compared to similar observation sites in France, Italy and Georgia this correlation is clearly more pronounced at UFS than at these other sites. During solar cycle 24 the increase of MLT temperatures was of similar magnitude as reported for previous cycles. However, the solar forcing was much weaker than during the previous cycles which leads to a strong relative forcing term of approximately 6°K/100 sfu. On short time scales, the eruption of the Hunga Tonga-Hunga Hapaai in January 2022, which included the emission of atmospheric waves travelling several times around the globe, was a truly remarkable event. Unique wave features were simultaneously observed in OH airglow at many VAO observatories. Especially, a remarkable wave of ca. 2 mHz (~ 8 minutes period) was observed for several hours at UFS Schneefernerhaus, Germany, at Sonnblick Observatory, Austria, at the Observatoire de Haute-Provence, France and at Otlica Observatory, Slovenia. These simultaneous observations provide an opportunity to conduct a detailed study of the complex dynamics associated with this event, which are discussed in this presentation.