“Physics o f Auroral P henom ena ' Proc. XXXVII A nnual Seminar, Apatity, pp. 113-116, 2014 © Kola Science Centre, Russian Academy o f Science, 2014 Polar Geophysical Institute NUMERICAL MODELING OF THE INITIAL STAGE OF THE ORIGIN OF CYCLONIC VORTICES IN THE VICINITY OF THE INTERTROPICAL CONVERGENCE ZONE I V. M ingalev1, N.M . Astafieva2, K.G. Orlov1, V.S. Mingalev1, O.V. Mingalev1, V.M. Chechetkin3 1 Polar Geophysical Institute, Apatity, Russia Space Reseach Institute, Moscow, Russia Keldysh Institute o f A p p lied Mathematics, Moscow, Russia Abstract. To investigate the initial stage of the origin of large-scale vortices at tropical latitudes a regional non hydrostatic mathematical model of the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized. 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 are produced by the utilized model. Simulations are performed for the case when the limited three-dimensional simulation domain is intersected by an intertropical convergence zone in the west-east direction. It was supposed that, at the initial moment, the intertropical convergence zone contains two convexities in the north direction. Time-dependent modeling was performed during the period of about four days. Simulation results indicated that three tropical cyclones were formed in the vicinity of the initial intertropical convergence zone in the course of time. Introduction It is known that the physical theory o f tropical cyclone formation is still far from completion. Nevertheless, some aspects o f tropical cyclogenesis are commonly understood, in particular, in the late stages of formation as well as in a fully developed stage [Emanuel, 1986; Montgomery and Farrell, 1993; Kieu and Zhang, 2008; Mao and Wu, 2011 and references therein ]. However, the important details of the initial stage of the formation of tropical large-scale vortexes are still unresolved. To investigate physical mechanisms responsible for the tropical cyclone formation, mathematical models may be utilized. Not long ago, in the Polar Geophysical Institute (PGI), a regional mathematical model of the wind system of the lower atmosphere has been developed [Belotserkovskii et al, 2006]. With the help of this model, it was shown that the origin of a convexity in the configuration of the intertropical convergence zone can lead to the formation of a cyclonic vortex during the period for about one day, with the cyclonic center being close to the southern edge of the initial intertropical convergence zone [Mingalev et al., 2011]. Moreover, the results of mathematical modeling have indicated that the origin of a convexity of the intertropical convergence zone, having the specific forms, can lead to the formation of not only a single cyclonic vortex but also a cyclonic-anticyclonic pair [Mingalev et al., 2012] and pair of cyclonic vortices [Mingalev et al., 2013], during the period not longer than three days. The purpose of the present work is to continue these studies, applying the regional mathematical model of the wind system of the lower atmosphere developed in the PGI, and to investigate numerically how the origin of convexities in the form of the intertropical convergence zone influence on the formation of the large-scale vortices. Mathematical model A regional mathematical model o f the wind system of the lower atmosphere, applied in the present study, has been developed in the Polar Geophysical Institute [Belotserkovskii et al., 2006] not long ago. In this model, the atmospheric gas is considered as a mixture of air and water vapor, in which two types of precipitating water (namely, water microdrops and ice microparticles) can exist. 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 peculiarity o f the model is that the vertical component of the air velocity is calculated without using the hydrostatic equation. Instead, the vertical component of the air velocity is obtained by means of a numerical solution of the appropriate momentum equation, with whatever simplifications of this equation being absent. Thus, the utilized 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 o f water vapor to micro drops of water and ice particles, which play an important role in energetic balance The three-dimensional simulation domain of the model is a part of a spherical layer stretching from land and ocean surface up to the altitude of 15 km over a limited region of the Earth's surface. In the present study, the dimensions of this region in longitudinal and latitudinal directions are 75° and 25°, respectively. The fimte- 113

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