Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

TIME-DEPENDENT MODELING OF THE INITIAL STAGE OF THE FORMATION OF CYCLONES IN THE INTRATROPICAL CONVERGENCE ZONE OF THE NORTHERN HEMISPHERE I.V. M ingalev1, N .M . A stafieva2, K.G. O rlov1, V.S. M ingalev1, O.V. M ingalev1 1Polar Geophysical Institute, Apatity, Russia 2Space Research Institute, Moscow, Russia A b s tra c t. A mathematical model o f the neutral wind system o f the lower atmosphere, developed recently, is utilized to investigate the initial stage of the formation of cyclones at tropical latitudes o f the northern hemisphere. The model produces three-dimensional distributions o f 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 an intratropical convergence zone. The results o f modeling indicate that the origin of a convexity of the form of the intratropical convergence zone can lead to the formation of a cyclone. Introduction One of the interesting problems o f the atmospheric dynamics is a genesis of tropical cyclones and hurricanes. Many of the details of the initial stage of the formation of tropical cyclones and hurricanes, however, are still unresolved. Mathematical models have the potential to make significant contributions to our knowledge of the processes responsible for the formation of tropical cyclones and hurricanes. Not long ago, a regional mathematical model of the neutral wind system of the lower atmosphere has been developed in the Polar Geophysical Institute (Belotserkovskii et al., 2006). In the above pointed out study, this model was applied to investigate the formation mechanisms of a large-scale vortex over a warm water band on the ocean surface. The results of modeling have allowed the authors to distinguish one o f the formation mechanisms of moderate cyclones over the ocean. Moreover, this mathematical model has been used in the study by Belotserkovskii et al. (2009) to investigate another mechanism of cyclone formation. It was shown that cyclones can appear in horizontal stratified shear flows o f warm and wet air masses with horizontal direction of gradients o f the wind velocity components as a result of small disturbances of pressure which can be produced by Rossby waves. The purpose of the present paper is to investigate the role of the shape of the intratropical convergence zone on the process of the formation o f cyclones by using the regional mathematical model, pointed out previously. B rief description o f the model In the utilized regional mathematical model, the atmospheric gas is considered as a mixture o f air and water vapor, in which two types of aerosols (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 characteristic feature o f the model is that the vertical component o f 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. 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 (Mingalev and Mingalev, 2005; Mingalev et al., 2007). Thus, the utilized mathematical model is based on numerical solving o f non-simplified gas dynamic equations and produces three-dimensional distributions o f the wind components, temperature, air density, water vapor density, concentration of micro drops of water, and concentration of ice particles in the height range from 0 to 15 km over a limited region o f the Earth's surface. The dimensions of this region in longitudinal and latitudinal directions are 32° and 25°, respectively. 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 o f water and ice particles, which play an important role. The finite-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 step and longitude step are equal to 0.08°, and height step is equal to 200 m. More complete details of utilized regional model may be found in the studies of Belotserkovskii et al. (2006, 2009). “P h ysics o f Auroral P hen om en a ", Proc. XXXIII A n n u a l Sem inar, Apatity, pp. 182 - 185, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute 182