SIMU LAT ION STUD Y OF THE IN IT IA L STAG E OF THE ORIGIN OF C Y C LO N IC AND AN T IC Y C LO N IC PA IRS IN THE IN TRA TRO P ICA L CO N V ER G EN C E ZONE I.V. Mingalev1, N.M. Astafieva2, K.G. Orlov1, V.S. Mingalev1, O.V. Mingalev1 ' Polar Geophysical Institute, Apatity, Russia 2Space Research Institute, Moscow, Russia Abstract. To investigate the initial stage of the formation o f large-scale vortexes at tropical latitudes of the northern hemisphere, the regional mathematical model of the neutral wind system of the lower atmosphere, developed recently in the PGI, is applied. 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 an intratropical convergence zone. Calculations were made for various cases in which the initial forms of the intratropical convergence zone were different and contained convexities with distinct shapes. The results o f modeling indicate that the origin of a convexity of the intratropical convergence zone, having the specific forms, can lead to the formation o f a pair of cyclonic and anticyclonic vortexes. Introduction A genesis of tropical large-scale vortexes, in particular cyclones, is one of the interesting problems of the atmospheric dynamics. Many of the details o f the initial stage of the formation of tropical large-scale vortexes, 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 large-scale vortexes. Recently, a regional mathematical model of the neutral wind system of the lower atmosphere has been developed in the Polar Geophysical Institute (Belotserkovskii et a l, 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 of the formation mechanisms of moderate cyclones over the ocean. Another formation mechanism o f a cyclone was investigated, using this mathematical model, in the study by Belotserkovskii et al. (2009). It was shown that cyclones can appear in horizontally stratified shear flows of warm and wet air masses with a meridional direction of gradients of the wind velocity components as a result of small disturbances of pressure which can be produced by Rossby waves. Besides, this mathematical model has been used in the study by Mingalev et al. (2011) to investigate a mechanism of the cyclone formation in the vicinity of the intratropical convergence zone. The results of modeling have indicated that the origin of a convexity of the form of the intratropical convergence zone can lead to the formation of a cyclone. The present paper is intended to investigate the role of the shape of the convexity of the intratropical convergence zone on the process o f the formation of a pair of cyclonic and anticyclonic vortexes by using the regional mathematical model, pointed out previously. Mathematical model In the applied mathematical model, the atmospheric gas is considered as a mixture of 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 of 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. 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 o f the Earth’s atmosphere (Mingalev and Mingalev, 2005; Mingalev et a l, 2007). In essence, the applied regional mathematical model is based on numerical solving of non-simplified gas dynamic equations and produces three-dimensional distributions of 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 of 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 Physics o fAuroral Phenomena ", Proc. XXXIVAnnual Seminar, Apatity, pp. 189-192 2011 Polar © Kola Science Centre, Russian Academy of Science, 2011 Ц>/Щ Geophysical \ V J Institute 189

RkJQdWJsaXNoZXIy MTUzNzYz