ИСТИНА

Polar Lows (hereafter PL) are intensive mesoscale cyclones, developing above the sea surface, usually behind the arctic front and characterized by severe weather conditions [1]. All in consequence of the global warming PLs started to emerge in the Russian Arctic water area as well – in summer and autumn, so that interest in natural recourses extraction and marine traffic in Arctic region causes the necessity of highquality PL forecasting. Lack of observational data and wide variety of PL types in different geographical and atmospheric conditions causes the absence of the «universal» concept of PL. This investigation is aimed at evaluation the role of various mechanisms in the dynamics of a particular real case of polar low development using mesoscale numerical simulations data. Quality of modelling was estimated by comparing model wind and water vapor fields with that received from satellite data. Two numerical experiments were conducted – including microphysics parameterization and switching it off (i.e. omitting phase transitions of water vapour). This has been done in order to assess the role of CISK mechanism. In order to divide low- and upper-level forcing in PL dynamics we used attribution concept applied to quasi-geostrophic (QG) omega equation. Prioir to that we ensured that QG theory could be used for this PL case. We have selected PL case in Kara sea occurred on 30th September 2008 Life span of the PL was between 24 to 36 hours. Numerical experiments were carried out with Weather Research and Forecasting model (WRF), which was installed on supercomputer “Lomonosov” of Research Computing Center of Moscow State University [3]. As initial conditions was used reanalysis data ERA-Interim from European Centre for Medium-Range Weather Forecasts. Two numerical experiments were made: with 5 km spatial resolution, explicit convection simulation and with Goddard center microphysical parameterization and without any vapor phase transformations. In order to conduct the modeling quality estimation we used visible and infrared images from MODIS (Aqua). Atmospheric water vapor V and surface wind fields W were resampled by examining AMSR-E microwave radiometer data (Aqua)[2]. Modeling fields were compared with satellite observations and shown good accordance. Then, dynamic characteristics were analyzed. We tested five main polar lows development concepts: convective and baroclinic instability, wind induced surface heat exchange, conditional instability of second kind and potential vorticity forcing [4]. Investigation showed, that neither baroclinic and convective instabilities nor WISHE mechanism triggered and intensified this PL development. Big CISK contribution to the PL increasing is noticeably visible from low-level PV anomaly intensification in “wet” experiment – it rises from 1 to 4,5 PVU during PL lifetime. Wind speeds and absolute vorticity decreases up to 2-3 units in “dry” experiment.The possibility of applying the quasi geostrophic theory to the mesoscale phenomena was shown with 0.78 correlation. Helmholtz-like quasi-geostrophic omega equation is planning to be resolved for three-dimensional forcing field, not for point or spherical sources, as [5,6]. Role of upper and lower level forcing will be estimated. Green’s function of lower PV anomaly penetrates to the upper-level anomaly location. References: 1. Polar lows, J. Turner, E.A. Rasmussen, 612, Cambridge University press, Cambridge, 2003. 2. Zabolotskikh, E. V., Mitnik, L. M., & Chapron, B. (2013). New approach for severe marine weather study using satellite passive microwave sensing. Geophysical Research Letters, 40(13), 3347–3350. doi:10.1002/grl.50664 3. V. Sadovnichy, A. Tikhonravov, Vl. Voevodin, and V. Opanasenko “Lomonosov”: Supercomputing at Moscow State University. In Contemporary High Performance Computing: From Petascale toward Exascale (Chapman & Hall/CRC Computational Science), pp.283-307, Boca Raton, USA, CRC Press, 2013. 4. B. J. Hoskins, M.E. McIntyre, A.W. Robertson, On the use and significance of isentropic potential vorticity maps, Quarterly journal of the Royal Meteorological Society, OCTOBER 1985, № 470, vol. 111(6). 5. Deveson, a. C. L., Browning, K. a., & Hewson, T. D. (2002). A classification of {FASTEX} cyclones using a height-attributable quasi-geostrophic vertical-motion diagnostic. Quarterly Journal of the Royal Meteorological Society, 128, 93–117. doi:10.1256/00359000260498806 6. Clough, S., Davitt, C., & Thorpe, A. (1996). Attribution concepts applied to the omega equation. Quarterly Journal of the Royal Meteorological Society, 122, 1943–1962. doi:10.1256/smsqj.53609