Large-scale characteristics of the optical instability of the Earth’s atmosphere (OIEA) up to the height of 30.5 km are being studied as calculated using data acquired at the aerological network throughout the CIS territory. The contributions of the boundary layer and free atmosphere to the OIEA over various regions during a year are estimated. Average duration of the optically calm periods of the atmosphere is determined. It has been established in this study that two cycles of the OIEA oscillations are observed over Yakutia and Far East during a year.