Data of ten-year measurements of the air temperature and pressure at the aerological network, and calculated root-mean-square values of the interdiurnal temperature difference at 15 standard pressure levels (down to 10 hPa) have been used to determine the root-mean-square values of the refractive index inhomogeneity for 50 aerological stations located on the CIS territory. Mean vertical profile of the air refractive index inhomogeneity has been determined for this territory. Using the root-mean-square values of the refractive index inhomogeneities, that characterize optical instability of the atmosphere, we have performed zoning of the CIS territory relative to this characteristic.
Qualitative comparison of the obtained characteristics of optical instability of the atmosphere to the observation data on the star image quality at three points: Novosibirsk, Mt. Sanglok (near Dushanbe), and at Pirkuli (near Baku), provided quite good results.