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.

“Physics o f Auroral P h en om en aP ro c. XXXVI Annual Seminar, Apatity, pp. 193 - 196, 2013 © Kola Science Centre, Russian Academy of Science, 2013 Polar Geophysical Institute SIMULATION STUDY OF THE MECHANISM OF THE FORMATION OF POLAR MESOSCALE CYCLONES AT HIGH LATITUDES OF THE NORTHERN HEMISPHERE I.V . M ingalev, K.G. Orlov, V .S. M ingalev (Polar Geophysical Institute, Apatity, Russia) A b s tra c t. A regional non-hydrostatic mathematical model of the wind system of the lower atmosphere, developed recently in the Polar Geophysical Institute, is utilized to investigate the mechanism of the formation of polar mesoscale cyclones at high latitudes of 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. The dimensions o f this region in longitudinal and latitudinal directions are 36° and 25°, respectively. Simulations are performed for the cases when this region is intersected by an arctic front, with the horizontal velocity field being asymmetric relatively the centerline of the arctic front inside and beyond it. Simulation results indicate that the origin o f a convexity in the configuration of the arctic front can lead to the formation of a polar mesoscale cyclone during the period for about one day. In tro d u c tio n A polar mesoscale cyclone (PMC) is an intense mesoscale atmospheric low pressure weather system (depression), involving strong winds, that originates over polar oceans in both the Northern and Southern hemispheres. Polar mesoscale cyclones have been referred to by other terms, such as polar low (PL), arctic hurricane, and cold air depression. Polar mesoscale cyclones are characterized by small sizes and short lifetimes in comparison with tropical cyclones. Nevertheless, polar mesoscale cyclones can cause wave surges, threat to ships, coastal flooding, and numerous fatalities for coastal communities. Therefore, prediction of polar mesoscale cyclone formation is a very important problem. Mathematical models have the potential to make significant contributions to our knowledge o f the processes responsible for the formation o f polar mesoscale cyclones. 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]. This 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. This regional model has been utilized in order to investigate numerically the mechanisms responsible for the formation of large-scale vortices over the ocean surface at tropical latitudes [Belotserkovskii et al., 2009; Mingalev et al, 201 lb, 2012b, 2013]. In pointed out studies, it was shown that the origin of convexities in the form of the intertropical convergence zone (ITCZ), having distinct configurations, can lead to the formation of different large-scale vortices, in particular, a cyclonic vortex, pair of cyclonic-anticyclonic vortices, and pair of cyclonic vortices, during the period not longer than three days. Also, the latter regional mathematical model has been applied to verify the hypothesis of the influence of the shape o f the arctic front on the initial formation of polar mesoscale cyclones. This hypothesis has been advanced and confirmed in the studies by Mingalev et al. [2011a, 2012a], In these studies, simulations were performed for two cases when, at the initial moment, the simulation domain is intersected by the arctic front with different configurations, with the fields o f the module o f the horizontal velocity being approximately symmetric relatively to the centerline of the arctic front not only inside it but also beyond the arctic front. The purpose of the present work is to continue the investigation of the initial stage of the formation of polar mesoscale cyclones at latitudes o f the European Arctic, applying the regional mathematical model of the wind system o f the lower atmosphere, developed in the PGI. Time-dependent modeling is performed for two cases in which the initial forms of the arctic front are different and contain convexities with distinct shapes, with the fields of the module of the horizontal velocity being asymmetric relatively to the centerline of the arctic front not only inside it but also beyond the arctic front. M a th em a tic a l m odel The regional non-hydrostatic mathematical model of the wind system of the lower atmosphere, developed not long ago at the Polar Geophysical Institute, is applied in the present work. In the applied 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 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 o f 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 193