Response of OH airglow temperatures and radiances to solar forcing between 2010 and 2023

Kurzfassung

Observations of OH airglow provide an important opportunity for tracing the variability of the mesosphere lower thermosphere (MLT) 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 UFS “Schneefernerhaus” (11.0°E, 47.0° N). Both OH temperatures and OH radiances show a positive correlation with solar activity (i.e. with F10.7cm). However, the increase of MLT temperatures during the maximum of solar cycle 24 was of similar magnitude as reported for previous cycles, despite the solar forcing being much weaker resulting in a strong relative forcing term of approximately 6 K/100 sfu. This suggests the presence of an indirect dynamical feedback rather than a direct forcing and there are indications for atmospheric solar tides playing an important role in this coupling. The high data quality allows for sophisticated analyses in the spectral range from days to years. These analyses reveal pronounced oscillations in the period range of 30 to 180 days between 2011 and 2015, followed by rather quite years until these oscillations reemerge again in 2020. The observations are confirmed by data from other NDMC sites. However, the physical nature of these oscillations and their apparent link to solar activity is not yet understood and open for discussion.