Vertical Distributions of Wind Characteristics at the Special Astrophysical Observatory

Abstract

This study utilizes multi-decadal reanalysis data to investigate upper-level wind speed and vorticity fields as key large-scale proxy indicators for atmospheric and optical turbulence dynamics above the Special Astrophysical Observatory (SAO) and Baikal Astrophysical Observatory (BAO). We considered the spatial and temporal variations in wind speed and atmospheric vorticity within the 9.5–13.6 km (300–150 hPa) layer at the SAO, located in the Caucasus Mountains, Russian Federation. Using hourly ERA5 reanalysis data over a 46-year period, from 1979 to 2025, we obtained seasonal spatial distributions over the SAO and evaluated long-term trends in the upper-level wind speed and vorticity using the non-parametric Mann–Kendall test. Spatial distribution analysis revealed subregions with strong upper-level winds across different seasons. Furthermore, three-dimensional atmospheric vorticity fields exhibited complex, multi-layered, and localized structures. For comparison, similar studies of large-scale proxy indicators were conducted for the BAO, located in the Baikal region of the Russian Federation. It is important to note that an additional analysis of long-term variations in optical turbulence strength was performed for BAO, utilizing the values of Cn2 calibrated against field measurements. These measurements were performed using a Shack–Hartmann wavefront sensor mounted on the Large Solar Vacuum Telescope. The accumulated wavefront-sensor measurements made it possible to adapt the model for calculation of optical turbulence strength Cn2 based on large-scale meteorological data. This study presents Cn2 long-term trend estimates for BAO. Analysis of these long-term trends indicates a potential impact of climate change on the optical turbulence characteristics.