The method of digital difference filters was applied to the analysis of OH and O2 rotational temperature observations in years 2010-2018 at altitudes of 85-90 km by photometers installed in Rikubetsu (43.5N, 143.8E) Shigaraki (34.8N, 136.1E) and Sata (31.0N, 130.7E) in Japan. Seasonal variations in the monthly-average values of rotational temperature and variance of perturbations with periods of 0.7 – 11 hours, which may be associated with internal gravity waves in the mesopause region, have been studied. Seasonal variations in the relative standard deviation of rotational temperature near the mesopause have maxima in winter and summer, also minima in spring and autumn. The details of the changes in the rotational temperature of OH and O2 may differ. This may be due to the different heights of the luminous layers. Currently, much attention is being paid to the study of internal gravity waves (IGWs). Their sources are mainly located in the lower layers of the atmosphere and, propagating upwards, IGWs are able to transfer energy and momentum into the middle and upper atmosphere, thus influencing the thermodynamic regime and dynamics of the atmosphere. Measuring the intensity and rotational temperature of nightglows is one of the ways to monitor the thermodynamic regime and composition of the upper atmosphere.