# Influence of Atmospheric Flow Structure on Optical Turbulence Characteristics
## 2 Used Methods  
Adaptation of the Weather Research and Forecasting Model within the Baikal Astrophysical Observatory Region  
Astronomical observations require high-quality diagnostics and prediction of the main atmospheric parameters, which determine the image quality. These parameters include wind speed components, air temperature, the refractive index at different heights in the atmosphere, as well as the Fried parameter and seeing. In order to study the influence of large-scale and meso-scale flows on small-scale turbulence, we chose the region where the Baikal Astrophysical Observatory (BAO) and Sayan Solar Observatory (SSO) are located. In this paper, we focus our attention on the Baikal Astrophysical Observatory. This observatory is located in Listyanka, 70 km from the city of Irkutsk. The main instrument in the observatory is the large solar vacuum telescope, which is located on a hilltop near Lake Baikal. The atmospheric circulation over the observatory has a complex character. The large-scale air flow interacts with the local mountain-valley air circulation. Episodic observations show that meso-scale jet streams are often observed above the observatory within the atmospheric boundary layer. For simulation of atmospheric flows over the observatory and Lake Baikal, we used the non-hydrostatic WRF model (version 3.9.1). The WRF model consists of a Eulerian mass solver with fully compressible non-hydrostatic equations, terrain following vertical coordinates and a staggered horizontal grid with complete Coriolis and curvature terms [25]. All the simulations were performed with the following constant 3D domains:  
1. The largest domain had a coarse grid with a horizontal resolution of 8 km over a \(1600\times 1600\) km area. The largest domain covered Lake Baikal, the Eastern Sayan mountains and surrounding areas, and included radio sounding stations (Angarsk and Nizhneudinsk). 2. The nested domain with a ratio of 1/4 corresponded to a \(400\times 400\) km area. The horizontal resolution in the domain was 2 km. 3. The smallest domain above the BAO had a fine horizontal resolution of 500 m. The area of interest was limited to \(100\times 100\) km. 4. There were 44 vertical levels, with higher resolution within the lower layers of the atmosphere. The number of height levels, up to 3100 m, was 12 (Figure 1). In higher layers of the atmosphere, the simulation was performed up to 30,800 m.  
Figure 2 shows three domain configurations for the WRF simulation. These domains are centred on the BAO. In comparison with Mount Graham (110 km northeast of Tucson, Arizona, United States), the site of the large binocular telescope, we performed a simulation within a larger area (\(1600\times 1600\) km). The outermost model size used by [PERSON] et al. was \(800\times 800\) km [26]. In addition, [PERSON] et al. used three nested domains in WRF simulations to search for the best site in the Ali area [27]. However, calculations were performed on a grid with lower horizontal resolutions (\(25\), \(5\) and \(1\) km, respectively). [PERSON] et al. used the same horizontal resolutions for estimating astronomical seeing above Dome A using the Polar WRF model [23]. Figure 1: The number of height levels, up to 3100 m.  
Figure 2: Three domain configurations for WRF simulation. The smallest domain covers the BAO, shown by the red marker, with 500 m horizontal grid resolution. The intermediate-sized domain covers the radiosounding station Angarsk. The largest domain is shown by the red rectangle. The Sayan Solar Observatory (SSO) and radio sounding station Nizhneudinsk are located in this domain. As the initial and boundary conditions, we used NCEP Global Forecast System (GFS) data. These initial data have a \(1\times 1^{\circ}\) horizontal resolution. The data assimilation system uses the maximum number of satellite and meteorological observations. Data assimilation and forecasts were made four times a day, at 00, 06, 12 and 18 UTC.