Physics of auroral phenomena : proceedings of the 37th Annual seminar, Apatity, 25 - 28 February, 2014 / [ed. board: A. G. Yahnin, N. V. Semenova]. - Апатиты : Изд-во Кольского научного центра РАН, 2014. - 125 с. : ил., табл.

I. V. Mingalev et al. difference method and explicit scheme are 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 0.08°, and height step is equal to 200 m. In the momentum equations for all components of the air velocity, the effect of the turbulence on the mean flow is taken into account by using an empirical subgrid-scale parameterization similarly to the global circulation model of the Earth’s atmosphere developed earlier in the PGI [ Mingalev 1. and Mingalev V, 2005; Mingalev et al., 2007]. More complete details of the applied regional mathematical model may be found in the studies of Belotserkovskii et al. [2006] and [Mingalev’ et al., 2013]. Simulation results In the present study, simulations are performed for the case when the three-dimensional simulation domain is intersected by an intertropical convergence zone in the west-east direction. It is known that an intertropical convergence zone may be considered as a fluid stream, having enhanced zonal velocities, in the ambient atmospheric gas, with a zonal flow of air being westward. A meridional wind velocity directs towards the centerline of an intertropical convergence zone at levels less than approximately 3 km and directs from the centerline of an intertropical convergence zone at levels higher than approximately 3 km. A vertical wind velocity in an intertropical convergence zone is upward. O 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Longitude (deg) 0 5 10 15 20 25 30 Figure 1. The distribution of horizontal component of the air velocity (m/s) at the altitude of 600 m, assigned at the initial moment. The degree of shadowing of the figure indicates the module of the velocity in m/s. In the earlier studies of Mingalev et al., [2012 and 2013], it was shown that the origin of convexities in the form of the intertropical convergence zone, having distinct configurations, can lead to the formation of different large-scale vortices, in particular, a cyclonic vortex, pair of cyclonic-anticyclonic vortices, and pair of cyclonic vortices, during the period not longer than three days. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Longitude (deg) 0 5 10 15 20 25 30 Figure 2. The distribution of horizontal component of the air velocity (m/s) at the altitude of 600 m, computed 20 hours after the beginning of calculations. The degree of shadowing of the figure indicates the module of the velocity in m/s. In the present work, simulations are performed for the case when the simulation domain is intersected by the intertropical convergence zone having the specific configuration. It was supposed that, at the initial moment, the intertropical convergence zone contains two convexities in the north direction, with the deviations achieving a value of a few hundreds of kilometers. The initial form of the intertropical convergence zone may be easy seen from the Figure 1. The time evolution of model parameters was numerically simulated using the mathematical model during the period for about four days. The results of time-dependent modeling are shown in Figures 2 and 3. The results of simulation indicate that, in the course of time, the initial distribution of horizontal component of the air velocity was considerably transformed. In a moment of 20 hours after the beginning of calculations, a pair of tropical cyclonic vortices arose. Their centers are close to the southern edge of the initial intertropical convergence 114