Statistical Estimates of the Vapor Content and Atmospheric Optical Thickness from Reanalysis and Radiosounding Data as Applied to Millimeter Telescopes

Possibilities of astronomical millimeter and submillimeter observations strongly depend on the precipitable water vapor (PWV), which determines the radiation absorption. The precise estimation of the PWV within large regions is one of key astroclimate problems. In this work, we refine estimates of the PWV for different sites based on processing ERA5 reanalysis and radiosounding data and test the previously suggested technique for correcting PWV values taking into account the characteristic water vapor vertical scale and the relative difference in grid node altitudes. In addition, the spatial distribution of the nighttime atmospheric optical thickness at a wavelength of 3 mm averaged over December–February 2013–2022 was derived for the first time for Russia and the adjacent territory. Our results can serve the basis for selecting an astronomic site for a new large millimeter telescope within the Eurasian Sub-Millimeter and Millimeter Telescope Project.