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.

Numerical simulation o f the initial stage o f theformation o f large-scale cyclonic vortices in the vicinity o f the intertropical convergence zone Simulation results From observation, it is known that, in an intertropical convergence zone, a zonal flow of air is westward, with the horizontal wind velocity being enhanced inside an intertropical convergence zone. A meridional wind velocity directs towards the centerline of an intertropical convergence zone at levels less than approximately 3 km and directs from the centerline of an intertropical convergence zone at levels higher than approximately 3 km. A vertical wind velocity in an intertropical convergence zone is upward. Therefore, an intertropical convergence zone may be considered as a fluid stream, having enhanced zonal velocities, in the ambient atmospheric gas. In our calculations, we define the initial and boundary conditions as consistent with the situation when the intertropical convergence zone intersects the simulation domain in the west-east direction. In the present work, we consider a case when, at the initial moment, the horizontal velocity field is asymmetric relatively the centerline of the intertropical convergence zone inside and beyond it. It was supposed that, at the initial moment, the intertropical convergence zone contains a convexity in the north direction, with the zonal wind velocities at more northern latitudes relatively the centerline of the intertropical convergence zone being larger than at more southern latitudes relatively it. The initial form o f the intertropical convergence zone may be easy seen from the top panel of the Fig. 1, where it is like a light curved band. It is noted that, in the considered case, the west crook of the convexity is sharp while the east crook of the convexity is gently sloping, with the east end of the convexity being 1° southern than the west crook of it. It can be noticed that the initial form of the intertropical convergence zone is chosen in accordance with the results of satellite microwave monitoring of the Earth’s atmosphere, included in the electron data base “GLOBAL- Field” ( http://www.iki.rssi.ru/asp ) , developed in the Space Research Institute of the RAS. This data base contains global radio thermal fields o f the Earth at the frequencies containing the information about a moisture and water integral content distribution in a troposphere. The data were obtained from the spacecraft mission, DMSP (Defense Meteorological Satellite Program), with the help of the instrument, SSM/I (Special Sensor Microwave / Imager). Studying results of satellite 20 15 S’ Ю -5 20 15 10 / / / / / / / / / / / / / / / i l l / / / / / / / / / / / / / / / / / / ' i i " E v f j f i 1 1' N43 / 1> 1 1 ' / ! v ' и ' . -*• S ■ ■_* ~ фМ > f. У “*•-".у-*--- ~-ч жил? f / ; / / t . f t t i t t / f . / / s ^ s s / / / / / / i t ,i; \-1 \ c;f v i :t -i; " v ' ■ ' ЧП L I t! 4.. \* \ \ \ \ \ \ \ \ \ \ \ \ \ \ . W . 4 — * Л ’X- V<\ \ -Л Л Л V \ ^ / ; / / ^ ^ ................ I r, > / / f ! I t / V, ! f t ' i I t ! I. l i t I f 1 s \ \ \ 1 t t 1 i' t >f.\ A .V f 20 15 10 10 15 20 25 30 -5 ,<■/ 7 7 / 7 7 7 7 7 / 1 i t" ! / I I ;i I ' l l t / / / / / / / / / / I / i 1 I I I I / / / / / / / ; / / / i / I l I I ‘ ' I i f I p \ i Г v ..„, ttf # ---------- > \ \ \ I I I I ! f t I N I. 1 \ \ \ N N V S W S N " . v v _ ^ ' -*■- / / / / / / / / / / / f / s S s . l i t I I t I f t I t / / / / ' / / / s s / S / / ' - ! I I I t I I I I > t t ! t I ,! / / / / S / / / / / • I 1 ! I 1 П 1 t 1 t t 1 C l I I I I I / t • ' .У.Л.УА.v 20 15 15 20 Longitude, deg 35 Fig. 2 The same as in Fig. 1, but computed 60 hours after the beginning of calculations (top panel), and computed 70 hours after the beginning of calculations (bottom panel). microwave monitoring of the Earth’s atmosphere, included in the electronic data base “GLOBAL- Field”, one can see that, sometimes, the Atlantic Ocean is intersected by an intertropical convergence zone stretched from Africa to South America. The time evolution of model parameters was numerically simulated using the mathematical model during the period for about three days. The results of time- dependent modeling are partly shown in Figs. 1 and 2. As can be seen from these figures, in the course of time, the initial distribution of horizontal component of the air velocity was considerably transformed. To a moment of 20 hours after the beginning of calculations, a cyclonic vortex flow arose whose center is close to the southern edge of the initial intertropical convergence zone. To a moment of 40 hours after the beginning of calculations, this cyclonic vortex has moved in the western direction for about 5 degrees. To a moment of 60 hours after the beginning of calculations, the rotational center of the formed cyclonic vortex has moved in the 191