Bogdan Rosa 1, Marcin Kurowski 1 and Michał Ziemiański 1 1. Institute of Meteorology and Water Management (IMGW), Warsaw Podleśna, 61 High resolution modeling of the Alpine convective flows using anelastic model EULAG Acknowledgements: Oliver Fuhrer 2, Piotr Smolarkiewicz 3, Andrzej Wyszogrodzki 3, Zbigniew Piotrowski 3 and Damian Wójcik 1 2. Meteo Swiss 3. National Center for Atmospheric Research COSMO General Meeting, Moscow September 2010

CONTENT 1. Introduction and motivation 2. Experiment setup 3. Meteorological situation 4. Simulation results 5. Summary and conclusions COSMO General Meeting, Moscow September 2010

Motivations and objectives We are interested in development of new generation dynamical core, for future NWP models for very high resolutions, (as a part of research- development work of the COSMO consortium, COSMO: Consortium of Small Scale Modeling, grouping some of European national weather services) Model requirements: - numerically robust, allowing for representation of effects of very steep, irregular orographies of high (eg. Alpine-type) mountain ridges - convection resolving, allowing for explicit simulation of ‘basic‘ deep convection events Practical test: assessment of performance of dynamical core for high resolution for high mountain and deep moist convection Scientific question: what is, ‘convection resolving model resolution’ for deep convection over high-mountains. COSMO General Meeting, Moscow September 2010

Scientific tools EULAG (EULarian semi-LAGrangian) nonhydrostatic anelastic model developed as a research tool at NCAR by P. Smolarkiewicz, J. Prusa, W. Grabowski and A. Wyszogrodzki see (Prusa and Smolarkiewicz, 2003; Smolarkiewicz and Prusa, 2005; Grabowski and Smolarkiewicz, 2002) The characteristic features of the EULAG model: - Conservative flux form of the governing equations - Semi-implicit time integration scheme - Finite volume discretization - Terrain following coordinates transformation - Capability of modeling flows over steep terrain. COSMO (Consortium of Small Scale Modeling) – operational nonhydrostatic compressible model, base on flow equations in advection form The characteristic features of COSMO model: - Explicit time integration scheme - Finite difference approximation in terrain following coordinates COSMO General Meeting, Moscow September 2010

Experiment description To perform a case study of simulation of the Alpine summer convection we used: - EULAG dynamical core with horizontal resolutions of 2.2, 1.1 and 0.55 km - simple representations of boundary layer processes: a) TKE turbulent kinetic energy b) ILES (no subgrid-scale model) + attenuation of heat surface fluxes in boundary layer - simple representation of moist processes (warm rain Kessler scheme) - initial and boundary conditions from operation run of COSMO2 model for Switzerland, with resolution of 2.2 km. For higher resolution 1.1km and 0.55km boundary condition are interpolated from the COSMO model (run 2.2 km). - orography: MeteoSwiss 2.2 km dataset or derived from 90m SRTM data for 1.1 and 0.55 km resolutions - compare the results with observations, especially satellite data COSMO General Meeting, Moscow September 2010

General meteorological situation in the Alpine region - 12 July 2006 MSG (Meteosat Second Genertion) 12:00 UTC Synoptic situation in the area: slow-moving cold front in a shallow surface trough of low pressure Synoptic map – 2:00 UTC, 12 July 2006 This is representative case study for summer (convective) situations. COSMO General Meeting, Moscow September 2010

Time evolution of convection in sequence of MSG satellite images ( visible and infrared in false colors) - 12 July 2006 MSG 9:00 UTCMSG 6:00 UTC MSG 12:00 UTC MSG 18:00 UTC MSG 15:00 UTC Onset of deep convection in the SW Alpine area occurs shortly before 12UTC, strong development between 12 and 15 UTC COSMO General Meeting, Moscow September 2010

Satellite images from NOAA. The view from low, polar orbit. High resolution sattelite images from 12 July 2006 NOAA 15:00 UTC NOAA 9:00 UTC COSMO General Meeting, Moscow September 2010

SETUP OF THE MODEL COSMO: 24 hour operational run of COSMO2 version of MeteoSwiss, for all parameterizations of subscale processes „on” EULAG: Start at 6:00 UTC Grid points, topography, model levels, horizontal domain as for COSMO2, terrain following coordinates up to top of the boundary domain. (COSMO has hybrid coordinates in Z) Moist processes represented by model developed by Grabowski and Smolarkiewicz see (Grabowski and Smolarkiewicz 2002) Drag at the boundary layer from COSMO. For higher resolution constant drag coefficient Initial and boundary conditions from COSMO2 No radiation COSMO General Meeting, Moscow September 2010

1. MOTIVATION Numerical complexity of EULAG simulations Horizontal resolution Domain size in grid points # processsors and machine ForecastWall clock time 2.2km520 x 350 x CRAY XT412 hours1h 10 min 1.1km1020 x 680 x CRAY XT47 hours~6 h 0.55km1020 x 1020 x CRAY XT5m12 hours~18 hours Number of levels is fixed and equal 61 in EULAG and 60 in COSMO. Vertical resolution changes from 10m at the bottom to several hundred meters at the tropopause. COSMO General Meeting, Moscow September 2010

Time evolution of cloud formation at resolution 2.2 km. Comparison between COSMO and EULAG. EULAG (TKE) - anelastic COSMO - compressible 6:00 UTC 9:00 UTC 15:00 UTC Resolution 2.2 km does not allow a development of the Alpine convection COSMO General Meeting, Moscow September 2010

Time evolution of specific humidity – vertical cross-section. Comparison of COSMO and EULAG simulations at resolution 2.2km EULAG (TKE) - anelastic COSMO - compressible The humid towers produced by EULAG are not observed in COSMO simulation COSMO General Meeting, Moscow September 2010

Time evolution of velocity flow field and specific humidity at =625m EULAG (TKE) - anelastic COSMO - compressible COSMO General Meeting, Moscow September 2010

Vertical component of velocity in EULAG simulations. Subgrid-scale model - TKE Resolution 2.2 kmResolution 1.1 km Higher resolution leads to incease of vertical velocity COSMO General Meeting, Moscow September 2010

Vertical velocity in EULAG simulation. Subgrid-scale model - TKE Resolution 2.2 kmResolution 1.1 km 0.5 COSMO General Meeting, Moscow September 2010 =2  U/N ≈9km

Cloud cover and stream lines from EULAG simulation at three different resolutions. 15:00 UTC Resolution 2.2km 13:00 UTC Resolution 1.1km 15:00 UTC Resolution 0.55km At resolution 0.55 km model starts to resolve the Alpine convection COSMO General Meeting, Moscow September 2010

Time evolution of cloud formation at resolution 0.55km. Results from EULAG model. 6:00 UTC 9:00 UTC 12:00 UTC 15:00 UTC 18:00 UTC Process of cloud formation starts shortly before 12 UTC COSMO General Meeting, Moscow September 2010

Verification of the EULAG simulation at resolution 0.55km. Situation at 18:00 UTC MSG 18:00 UTC 18:00 UTC COSMO General Meeting, Moscow September 2010

1. MOTIVATION CONCLUSIONS EULAG is robust for Alpine orography and with simple physics The model starts to resolve the convection over SW Alps at resolution of 0.55 km Even at resolution 0.55km the model is still far from representation of organization of deep convection Further experiments needed with more realistic representation of physics (PBL, possibly radiation) COSMO General Meeting, Moscow September 2010