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.

zone. Approximately 30 hours later, third tropical cyclone arose whose center is close to the southern edge of the initial intertropical convergence zone. The arisen cyclonic vortices have moved in the western direction. The radii of these three cyclones are about 800 km. The horizontal wind velocity in the cyclones can achieve values of 15-20 m/s in the course of time. The simulation results indicate that a key factor in the modeled formation of the triplet of tropical cyclonic vortices is the origin of convexities in the configuration of the intertropical convergence zone. The origin of these convexities leads to beginning of instability of stream air flow. This instability leads to considerable transformation of the wind field. As a consequence, the triplet of tropical cyclonic vortices arises in the lower atmosphere in the course of time. In addition to that, the initial intertropical convergence zone is broken down. Numerical modeling o f the initial stage o f the origin o f cyclonic vortices in the vicinity o f the intertropical convergence :one 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 Longitude (deg) — ■ — — ШШШШЯШШШ/ШШШШШЯШЛ ..l ШПШЯЯШШ . : I i 0 5 10 15 20 Figure 3. The distribution of horizontal component of the air velocity (m/s) at the altitude of 600 m, computed 90 hours after the beginning of calculations. The degree o f shadowing of the figure indicates the module of the velocity in m/s. It can be noticed that, according to observations, not each cyclonic vortex, arisen in the lower atmosphere, has the potential to grow up to the long-live large-scale atmospheric vortex. It is known that, sometimes, a vortex, initially arisen in the lower atmosphere, can be attenuated in the course of time and will not achieve a status of the long-live large-scale atmospheric vortex. This peculiarity may take place for the large-scale vortices arisen in the calculations of the present study, which were limited by the time intervals not longer than four days. Unfortunately, more prolonged time intervals are impossible for the utilized mathematical model because of limited sizes of its simulation domain and owing to tendency of the modeled vortices to move and to abandon the simulation domain in the course of time. Conclusions In earlier studies by the authors o f the present work, the idea has been advanced that the transformation of the shape of the intertropical convergence zone can influence the process of the formation of tropical cyclones [Mingalev et al., 2013 and references therein ]. The present work is the continuation of the investigation of the initial stage of the origin of large-scale vortices at tropical latitudes. For this investigation, a regional non-hydrostatic mathematical model o f the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized. The model is based on the numerical solution of the system of transport equations containing the equations of continuity for air and for the total water content in all phase states, momentum equations for the zonal, meridional, and vertical components of the air velocity, and energy equation. 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. Simulations are performed for the case when this region 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 simulation results indicated that the twin tropical cyclones were formed during the period for about 20 hours. Their centers are close to the southern edge of the initial intertropical convergence zone. Besides, to a moment o f approximately 50 hours after the beginning of calculations, third tropical cyclone arose whose center is close to the southern edge of the initial intertropical convergence zone, too. The arisen triplet of tropical cyclonic vortices has moved in the western direction. The radii of these three cyclones are about 800 km. The horizontal wind velocity in the cyclones can achieve values of 15-20 m/s in the course of time. A cknow ledgm en ts. This work was partly supported by Grant No. 13-01-00063 from the Russian Foundation for Basic Research. 115