Conclusion. The method of digital differential filters (2) is applied to the
analysis of observations of the rotational temperature of hydroxyl nightglow at altitudes of 85—90 km with the SATI device in Alma-Aty, Kazakhstan in years 2010—2017. Analyzed are interannual and seasonal changes in the monthly-mean temperature and characteristics of temperature perturbations with mesoscale periods, which may be associated with IGW in the mesopause region. To obtain variations with time periods of 1.7—5 h a numerical filtering was used by calculating the differences between consecutive hourly-mean temperature values. The mean temperature near the mesopause has a maximum in winter and minimum in June. IGW intensities maximize in spring and autumn and minimize in winter and summer. The slopes of regression lines in Figs. 3b—3d correspond to multi-year increasing intensity of mesoscale perturbations near the mesopause.