X-shooter-based climatologies of intensity, solar cycle effect, and residual variability for 298 OH lines

The line emission from the various roto-vibrational bands of the OH radical is an important tracer of the chemistry and dynamics in the Earth's nocturnal mesopause region between about 80 and 100 km. As most studies have focused either on a few bright lines or integrated emission from relatively wide wavelength windows, there is still a lack of knowledge with respect to the variability of faint lines from high rotational levels as well as the change of the variability patterns depending on the line parameters, which influence the effective emission height. Thanks to a large data set of about 90,000 near-infrared X-shooter spectra taken at Cerro Paranal in Chile within a time interval of 10 years, we have been able to derive line-specific climatologies of intensity, solar cycle effect, and residual variability for local time and day of year based on a set of 298 OH lines. Our analysis of the derived climatologies involves different decomposition techniques, the study of the variance depending on the time scale of the perturbation, and the calculation of correlations for the line dependence of different properties. The considered effective line emission heights originate from the investigation of the propagation of a strong quasi-2-day wave in 2017 using the X-shooter and space-based SABER data. Our results for the entire X-shooter data set reveal the importance of the mixing of thermalised and non-thermalised rotational populations for the amplitude of a perturbation as well as a shift of the climatological variability patterns with local time depending on the emission height. The latter implies a strong influence of the migrating diurnal tide and causes significant line-dependent differences in the effective solar cycle effect, which mainly depends on the solar forcing in the austral winter.