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The study analyzes the long-term average annual OH* temperature trend, the values of which were obtained from nighttime spectral measurements of hydroxyl airglow bands at Zvenigorod research station (56° N, 37° E) from 1957 to 2022. At present, this OH* temperature series, which reflects the thermal state of the mesopause region, is the longest in the world. On its basis, the linear trend and response of temperature to changes in solar activity are estimated both in general for the entire data set and for individual time intervals. In the first case, the trend was –0.23 ± 0.04 K/year. In the second case, the analysis showed a strong cooling in the mesopause region (–0.53 ± 0.34 K/yr) until the 1970s, which subsequently slowed to –0.14 ± 0.03 K/yr. Comparison of the results with other measurements and model calculations shows that the latter have lower trend values. It is suggested that the causes of the temperature trend, in addition to the increase in greenhouse gases, the main one being CO2, can be due to long-term changes in the dynamics of the upper atmosphere. [ABSTRACT FROM AUTHOR]

The influence of the 27-day solar oscillation on the temperature and intensity of the airglow of the mesopause region based on the hourly midnight observations of the О2А(0-1) and ОН(6-2) bands at the Zvenigorod Scientific Station in 2000−2021 has been studied. It is found that the response to solar activity changes is observed in all characteristics of the atmospheric emissions both by the yearly and seasonal data. They are statistically significant for all characteristics of the atmospheric emissions in winter and only for the О2А(0-1) intensity in summer. The positive response of the molecular oxygen emission is lower in the summer than in the winter by approximately a factor of 2. It is found that the variations in the atmospheric emission characteristics are close to antiphase with a 27-day solar oscillation. At the same time, the temperature of the emitting hydroxyl in winter undergoes oscillations with a shift by a third of the period relative to the solar variation maximum. [ABSTRACT FROM AUTHOR]

Spectral observations of the mesopause airglow at the Zvenigorod Scientific Station have been used to obtain the midnight emission intensities of molecular oxygen (О2А(0-1) band) and hydroxyl (OH (6-2) band) for 2000–2019. Spectral analysis of the variations has made it possible to determine the annual variability for each emission, which is described by the sum of four harmonics. The time lag in seasonal variations of the hydroxyl emission relative to variations in the emission of molecular oxygen is 5–18 days. Long-term changes in the average annual emission intensities have been studied. The linear trend (–3.3 ± 0.3% per year for О2А(0-1) and –2.6 ± 0.2% per year for ОН(6-2)), the dependences on the 11-year solar cycle (response to changes in the Lyman-alpha solar radiation (18.5 ± 3.3% per 1011 photons cm–2 s–1 for О2А(0-1) and 10.5 ± 2.5% per 1011 photons cm–2 s–1 for OH (6-2)) and the 22-year solar cycle (response to changes in the solar magnetic field strength (23.2 ± 4.5% per 100 μТ for О2А(0-1) and 12.1 ± 3.5% per 100 μТ for ОН (6-2)), as well as quasi-eight-year oscillations have been found. [ABSTRACT FROM AUTHOR]

The summer mesopause region (altitudes of 82–92 km) is the coldest place in the Earth's atmosphere; it is influenced by external effects, including lunar tides. In this study, we isolate the lunar tidal harmonics from the temperature series of the hydroxyl emission layer (OH*) obtained from spectrophotometric measurements at the Zvenigorod scientific station of the Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, in the summer seasons of 2000–2016. The OH* temperatures are the weighted average in a layer of ~9 km thick, which has a maximum at an altitude of ~87 km. The analysis made it possible to distinguish lunar oscillations, among which two harmonics in the temperature of the mesopause region are identified for the first time. These oscillations are recognized as the second harmonic of the anomalistic lunar tide (the mean period is ~13.78 days) and the lunar tide with a period of 8 h 17 min, or, interpreting alternatively, the third harmonic of the lunar synodic month (~9.84 days). [ABSTRACT FROM AUTHOR]

New results of research on lunar tides in the midlatitude mesopause region are presented. According to observational data on noctilucent clouds and spectrophotometric measurements of hydroxyl radiation, among the semimonthly and semidiurnal lunar tidal harmonics under consideration, the semimonthly zonal tide (13.66 days), semimonthly synodic tide (14.77 days), and semidiurnal tide (12 h 25 min) were proven to be statistically significant. The temperature oscillations in the summer hydroxyl layer and the brightness of noctilucent clouds turned out to be nearly out of phase. For the first time, we considered two possible mechanisms of the generation of the synodic semimonthly harmonic. Here, statistical analysis of the hydroxyl data shows that the nonlinear demodulation of the superposition of solar and lunar semidiurnal tidal harmonics is the most probable process. [ABSTRACT FROM AUTHOR]