Physics of auroral phenomena : proceedings of the 36th Annual seminar, Apatity, 26 February – 01 March, 2013 / [ed. board: A. G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2013. - 215 с. : ил., табл.

I. V. Mingalev at al. Now, let us consider the second case when, at the initial moment, the arctic front contains a convexity in the north direction, with the fields of the module of the horizontal velocity being asymmetric relatively to the centerline of the arctic front not only inside it but also beyond the arctic front. The initial form of the arctic front may be easy seen from the top panel of the Fig. 2, where it is like a dark curved band between two light curved bands. The center of the bent part o f the front is 27° eastward from the western boundary of the simulation region. The time evolution of atmospheric parameters was numerically simulated using the mathematical model during the period for about two days. The results of time-dependent modeling are partly shown in Fig. 2. The simulation results presented in Fig. 2 show that, at the presence at the initial moment of the part of the arctic front bent to the north, when the fields of the module of the horizontal velocity are asymmetric relatively to the centerline of the arctic front, westward from this part, approximately in 20 h, a polar mesoscale cyclone is formed which moves to the south and to the west with a velocity of approximately 5-10 km/h. The maximum wind velocity within the polar mesoscale cyclone is reached approximately 20 h after the simulation beginning, and then it begins to decrease slowly. The radius of this polar mesoscale cyclone is about 600-800 km. Conclusions A regional non-hydrostatic mathematical model of the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized to investigate the mechanism of the formation of polar mesoscale cyclones at high latitudes of the northern hemisphere. The model produces three-dimensional distributions of the atmospheric parameters in the height range from 0 to 15 km over a limited region of the Earth's surface. The dimensions of this region in longitudinal and latitudinal directions are 36° and 25°, respectively. The southern boundary of the simulation region was located at 55° N. It was supposed that, at the initial moment, this region is intersected by an arctic front, which contains the convexity in the north or south directions, moreover, the fields of the module of the horizontal velocity are asymmetric relatively to the centerline o f the arctic front. The simulation results indicated that the origin of a convexity in the configuration o f the arctic front, having the latitudinal dimension o f about 600 km and the deviation of hundred of kilometers either in north or south direction, can lead to the formation of polar mesoscale cyclones during the period of about one day. The polar mesoscale cyclone has a horizontal extent of about 600-800 km. The horizontal wind velocity in this polar mesoscale cyclone can achieve values of 15-20 m/s during the period o f 20 hours. The simulation results show that the key factor in the mechanism of the formation o f polar mesoscale cyclones is the origin of a convexity in the configuration of the arctic front. As a consequence, instability of the shear air flow arises. This instability leads to considerable transformation of the wind field. As a result, polar mesoscale cyclones may be formed in the vicinity of the initial position of the arctic front in the course of time. A cknow ledgm en ts. This work was partly supported by the RFBR grant 13-01-00063. References B elotserkovskii, O .M , I.V . M ingalev, V .S. M ingalev, O .V. M ingalev, A .M . 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M ingalev, N um erical sim ulation o f form ation o f cyclone vortex flow s in the intertropical zone o f convergence and their early detection, Cosm ic Research, V. 50(3), 233-248, 2012b. M ingalev, I .V , N .M . A stafieva, K .G . O rlov, V.S. M ingalev, O.V . M ingalev, and V .M . C hechetkin, A sim ulation study o f the form ation o f large-scale cyclonic and anticyclonic vortices in the vicinity o f the intertropical convergence zone, IS R N G eophysics, V. 2013, A rticle ID 215362, 12 pages, doi: 10.1155/2013/215362, 2013. 196