Atmospheric Conditions within Big Telescope Alt-Azimuthal Region and Possibilities of Astronomical Observations

Abstract

The paper presents the results of analysis of astroclimatic conditions in the Big Telescope Alt-azimuthal (BTA) region (40°N–50°N; 35°E–55°E). Using data from the European center for medium-range weather forecast ReAnalysis (ERA-5), we estimated the averaged spatial distributions in total cloud cover, vertical integral of mean kinetic energy, vertical component of wind speed, and wind speed shears, as well as inverse values of Richardson number 1/Ri. An extensive region with the development of atmospheric flows is formed south and southeast of BTA in winter. High inverse values of the Richardson number, spatial heterogeneities in vertical wind speed, and significant wind speed shears in the lower atmosphere are observed in this region. In terms of turbulence development over BTA, the best time for astronomical observations falls in summer, when vertical shears of wind speed are weakened in the lower atmospheric layers. The situation is opposite in the upper troposphere. In winter, BTA is in the region of moderate vertical wind shears. In summer, a region with increased vertical wind speed shears is formed. Taking into account that the intensity of optical turbulence decreases rapidly with height, better image quality can be expected in summer. Such structure of the atmosphere does not allow one to directly apply atmospheric models in order to describe turbulence based on the turbulence strength as function of its ground values, or to use the classical model describing the turbulence velocity as function of air flow velocity at the height corresponding to the 200 hPa level.