Abstract: Temporally coherent mesoscale perturbations of the rotational temperature of excited hydroxyl (OH*) are often used as an indicator of wave processes in the mesosphere and lower thermosphere. Digital filters are used in this study to determine the mesoscale component with periods of 0.8–11 h, based on the differences in measured values shifted in time by fixed intervals varying from 10 min to 2 h. The average monthly intensity of mesoscale variations is proportional to the variance of the indicated differences recorded in each calendar month of measurements. These variances contain both information about coherent mesoscale processes and also temporally incoherent noise of an instrumental and turbulent nature. A statistical method for the analysis of the structural functions of the analyzed characteristics of nighttime airglow was developed and applied to estimate the variance of incoherent random noise. These estimates are subtracted from the measured monthly mean variances of mesoscale differences in order to obtain information on the intensity of coherent mesoscale processes near the mesopause. Subtraction of the variance of incoherent noise does not change the character of seasonal variations in all spectral intervals, but it decreases the values of mesoscale standard deviations by 10–20%. The proposed correction makes it possible to better determine the features of seasonal and interannual changes in coherent mesoscale disturbances in different ranges of the frequency spectrum.