Physics of auroral phenomena : proceedings of the 38th annual seminar, Apatity, 2-6 march, 2015 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Издательство Кольского научного центра РАН, 2015. - 189 с. : ил., табл.

Self-consistent numerical modeling o f the global wind system and heat regime o f the tower and middle atmosphere velocity are obtained by means of a numerical solution of the generalized Navier-Stokes equation, with the effect of the turbulence on the mean flow being taken into account by utilizing an empirical subgrid-scale parameterization similarly to the global circulation model of the Earth’s atmosphere developed earlier in the PGI [Mingalev I. and Mingalev V., 2005; Mingalev et al., 2007]. Thus, the new version of the mathematical model is based on numerical solving of non-simplified gas dynamic equations and produces three-dimensional time-dependent distributions of the wind components, temperature, air density, water vapor density, concentration of micro drops of water, and concentration of ice particles. The model takes into account heating / cooling of the air due to absorption / emission of infrared radiation, as well as due to phase transitions of water vapor to micro drops of water and ice particles. The fmite-difference method is applied for solving the system of governing equations. The calculated parameters are determined on a uniform grid. The latitude and longitude steps are equal to 0.94°, and height step is equal to 200 m. The simulation domain is a layer surrounding the Earth globally. The planetary surface is assumed to be a smooth spheroid. The lower boundary is the Earth’s surface, whereas, the upper boundary is the sphere lain at the altitude of 75 km over the equator sea level. Simulation results In the present study, simulations were performed for one concrete situation. The initial moment of the calculations has corresponded to 10.30 UT for 16 January that is for winter in the northern hemisphere. Simulations were performed for conditions corresponding to moderate solar activity (F 10.7 = 101) and low geomagnetic activity (Kp=l). At the initial moment, the neutral gas density at the lower boundary and air temperature in all simulation domain were taken from the NRLMSISE-00 empirical model [Picone et al., 2002], moreover, all components of the neutral wind velocity were equal to zero. The variations of the atmospheric parameters with time were calculated during the period for about four hundreds of hours. It turned out that the three-dimensional global distributions of the gas dynamic parameters of the lower and middle atmosphere, calculated with the help of the model, changed essentially after initial moment. Maximal absolute values of the horizontal and vertical components of the air velocity are larger at higher altitudes. The gas dynamic parameters, in particular the zonal, meridional, and vertical components of the air velocity, are changeable functions not only of latitude and longitude but also of altitude. The distribution of the vector of the horizontal component of the neutral wind velocity as function of longitude and latitude at the altitude of 50 km is shown in Fig. 1. It is seen that, at levels of the mesosphere, the horizontal wind velocity can achieve values of more than 70 m/s. F ig u r e 1. The distribution of the vector of the calculated horizontal component of the air velocity (m/s) as function of longitude and latitude at the altitude of 50 km, computed 412 hours after the beginning of calculations. The degree of shadowing of the figure indicates the module of the velocity in m/s. The distribution of the neutral gas temperature as function of longitude and latitude at the altitude of 50 km is shown in Fig. 2. It can be seen that the neutral gas temperature in the southern hemisphere is larger than that in the northern hemisphere. This fact is not extraordinary because of, in January, winter is in the northern hemisphere, whereas, summer is in the southern hemisphere. It is well known from numerous observations that the global atmospheric circulation can contain sometimes so called circumpolar vortices. In the global neutral wind system, these vortices are the largest scale inhomogeneities which are formed at heights of the stratosphere and mesosphere in the periods close to summer and winter solstices. It is know that, in the northern hemisphere, the circumpolar anticyclone arises under summer conditions, whereas, the circumpolar cyclone arises under winter conditions. In the southern hemisphere, the circumpolar cyclone arises under winter conditions, whereas, the circumpolar anticyclone arises under summer conditions. 182