Abstract <p>Requirements for elements and efficiency of adaptive optics (AO) systems are largely related to atmospheric conditions at their locations. The primary task in developing AO systems is still to provide a photon flux sufficient for the operation of wavefront sensors from a sodium laser guide star (LGS). One of ways of increasing the photon flux is LGS formation with the use of circularly polarized laser radiation, which is related to the influence of the Earth’s magnetic field on energy levels of the sodium atom. The features of Siberian observatories are the geomagnetic field magnitude of 56–58 nT, which is considerably higher than that of any known observatory in the world, and the low (about 2 × 10¹³ atoms/m²) density of sodium atoms in the mesosphere in summer. This paper presents results of numerical simulation of the return photon flux from a sodium LGS for atmospheric conditions in Siberia. Approaches to increasing the LGS brightness are considered. The results can be used in developing AO systems of ground-based telescopes for observing natural and artificial space objects.</p>