A response of the polar winter upper mesosphere to short-period solar variations

Abstract. Effects of short-period variations in the flux of solar UV radiation on the intensity of airglow emissions coming from the hydroxyl (OH) airglow layer and temperature variations in the upper mesosphere over Kiruna, Sweden, have been investigated. Measurements were performed with the OH airglow imager, measuring selected emission lines in the OH(3-1) Meinel band. Measurements for four winter seasons from 2022 to 2026 have been considered. Solar activity is represented by diurnal flux changes in the Lyman alpha (α) line. It has been shown that short-period changes in the Lyman–α flux lead to statistically significant changes in the temperature and intensity of OH(3-1) emissions with a positive response and with about zero time delay (0–5 days). This result indicates the dominance of the mechanisms of direct radiative and photochemical influence of Lyman–α on change in the physical-chemical state of the polar winter upper mesosphere. Average temperature amplitudes due to short-period changes in the Lyman–α flux are approximately 2–4 K, which are comparable in magnitude to temperature variations due to atmospheric planetary waves. A relationship has been found between characteristic features of the power spectrum of the Lyman–α flux and the time delay in the mesospheric response at time intervals of about 4–6 months.