TY - CHAP A1 - Klein, Marten A1 - Ghasemi, Abouzar A1 - Seelig, Torsten A1 - Borcia, Ion-Dan A1 - Harlander, Uwe A1 - Will, Andreas T1 - Mean flow generation and inertial wave attractors in a librating annulus: DNS and theory T2 - European Geosciences Union, General Assembly 2015, Vienna, Austria, 13 April - 17 May 2015 KW - boundary-layer structure KW - direct numerical simulation KW - instability KW - waves in rotating fluids Y1 - 2015 UR - http://meetingorganizer.copernicus.org/EGU2015/EGU2015-15640-1.pdf N1 - EGU2015-15640-1 PB - European Geophysical Society CY - Katlenburg-Lindau ER - TY - CHAP A1 - Klein, Marten A1 - Ghasemi, Abouzar A1 - Seelig, Torsten A1 - Borcia, Ion-Dan A1 - Harlander, Uwe A1 - Will, Andreas T1 - DNS of inertial wave attractors in a librating annular cavity with a height-dependent gap T2 - ICTW 19, Book of Abstracts, 19th International Couette-Taylor Workshop, June 24 - 26, 2015 Cottbus, Germany KW - waves in rotating fluids KW - geophysical and geological flows KW - direct numerical simulations Y1 - 2015 SP - 122 EP - 123 CY - Cottbus ER - TY - CHAP A1 - Klein, Marten A1 - Borcia, Ion-Dan A1 - Egbers, Christoph A1 - Ghasemi, Abouzar A1 - Harlander, Uwe A1 - Kurgansky, Michael V. A1 - Schaller, Eberhard A1 - Seelig, Torsten A1 - Will, Andreas T1 - Inertial Waves and Wave Excitation Mechanisms in Annular Cavities: Simulations, Experiments and Theory T2 - European Turbulence Conference ETC14, Lyon, 2013 KW - boundary-layer structure KW - geophysical and geological flows KW - waves in rotating fluids Y1 - 2013 UR - http://etc14.ens-lyon.fr/etc-14-proceedings/accepted-talks ER - TY - CHAP A1 - Klein, Marten A1 - Ghasemi, Abouzar A1 - Harlander, Uwe A1 - Will, Andreas T1 - Inertial wave excitation and wave attractors in a librating annulus: DNS T2 - European Geosciences Union, General Assembly 2014, Vienna, Austria, 27 April – 02 May 2014 KW - boundary-layer structure KW - geophysical and geological flows KW - waves in rotating fluids KW - direct numerical simulations Y1 - 2014 N1 - EGU2014-15585 PB - European Geophysical Society CY - Katlenburg-Lindau ER - TY - GEN A1 - Ogaja, Jack A1 - Will, Andreas T1 - Fourth order, conservative discretization of horizontal Euler equations in the COSMO model and regional climate simulations T2 - Meteorologische Zeitschrift N2 - Horizontal spatial schemes of third order and above used for discretization of COSMO (Consortium for Small Scale Modeling) Euler equations can be described as quasi-higher order schemes since interpolation of the advecting velocities and differencing of the pressure gradient term remain second order accurate. For NWP and Regional Climate modeling, upwind schemes of either third or fifth order have been recommended combined with an explicit numerical diffusion. We have implemented fully fourth order central difference horizontal schemes for the model’s Euler equations with two types of discretization of the advection terms: the first is a natural extension of the COSMO fourth order scheme by introducing fourth order interpolation of the advecting velocity, and the second is a symmetric type discretization which is shown to conserve the rotational part of kinetic energy. We combine both advection schemes with fourth order discretization of the pressure gradient term. To make the schemes completely fourth order, we consider all metric terms resulting from coordinated transformations. Theoretical analysis of the new schemes compared to the model’s existing third order upwind scheme exhibits: a slightly increased group velocity error due to a wider stencil, a similar dispersive error, a significant reduction of the amplitude error, a significantly minimized aliasing error due to symmetric advection-discretization, and a significant increase in effective Courant number which potentially allows longer time steps. Using 20-year climate simulations, we show that the new symmetric fourth order scheme is more stable than the extended COSMO fourth order scheme and third order upwind scheme, and that an explicit numerical diffusion can be avoided when using the symmetric scheme. We show that a 20% dispersive (phase) and diffusive (amplitude) errors limit result to the model’s effective resolution of approximately 5Δx for all 4th and 3rd order schemes. Considering the same error limit for simulated kinetic energy spectra show that the horizontal numerical diffusion is reducing the model’s effective resolution to more than 10Δx and thus using the symmetric 4th order scheme without explicit horizontal diffusion increases the effective resolution by a factor of two to approximately 5Δx. We further show that both implicit diffusion in upwind schemes and explicit numerical diffusion necessary for the current model’s stable runs have effects of equal magnitude on the model’s predicted climatologies. Climatologies show that fourth order schemes enhance vertical turbulence mixing in the planetary boundary layer which reduces parameterized convection. This consequently results to approximately 20% peak reduction of summer precipitation and an increase of approximately 0.5 degrees Kelvin in summer 2m air temperature. KW - Climate KW - modelling KW - regional KW - numerics KW - spatial scheme KW - higher order KW - meteorology KW - climatology KW - diffusion KW - energy conservation Y1 - 2016 U6 - https://doi.org/10.1127/metz/2016/0645 SN - 1610-1227 VL - 25 IS - 5 SP - 577 EP - 605 ER - TY - GEN A1 - Ghasemi, Abouzar A1 - Klein, Marten A1 - Harlander, Uwe A1 - Kurgansky, Michael V. A1 - Schaller, Eberhard A1 - Will, Andreas T1 - Mean flow generation by Görtler vortices in a rotating annulus with librating side walls T2 - Physics of Fluids N2 - Time periodic variation of the rotation rate of an annulus induces in supercritical regime an unstable Stokes boundary layer over the cylinder side walls, generating Görtler vortices in a portion of a libration cycle as a discrete event. Numerical results show that these vortices propagate into the fluid bulk and generate an azimuthal mean flow. Direct numerical simulations of the fluid flow in an annular container with librating outer (inner) cylinder side wall and Reynolds-averaged Navier–Stokes (RANS) equations as diagnostic equations are used to investigate generation mechanism of the retrograde (prograde) azimuthal mean flow in the bulk. First, we explain, phenomenologically, how absolute angular momentum of the bulk flow is mixed and changed due to the propagation of the Görtler vortices, causing a new vortex of basin size. Then we investigate the RANS equations for intermediate time scale of the development of the Görtler vortices and for long time scale of the order of several libration periods. The former exhibits sign selection of the azimuthal mean flow. Investigating the latter, we predict that the azimuthal mean flow is proportional to the libration amplitude squared and to the inverse square root of the Ekman number and libration frequency and then confirms this using the numerical data. Additionally, presence of an upscale cascade of energy is shown, using the kinetic energy budget of fluctuating flow. KW - Direct Numerical Simulation KW - Fluid Mechanics KW - Mean Flow KW - Rotation KW - Cylinder KW - Centrifugal KW - Instability KW - Mechanism KW - Vortex Y1 - 2016 U6 - https://doi.org/10.1063/1.4948406 VL - 28 IS - 056603 SP - 1 EP - 23 ER - TY - GEN A1 - Will, Andreas A1 - Ogaja, Jack T1 - Higher order horizontal schemes in COSMO 5 . 0 at different resolutions T2 - CLM-Community Newsletter KW - COSMO-CLM KW - Climate KW - Regional Climate Model KW - Numerical Methods KW - Higher Order Scheme KW - Numerical Diffusion KW - Meteorology KW - Geophysical Fluid Dynamics Y1 - 2017 VL - 8 SP - 7 EP - 8 ER - TY - GEN A1 - Weiher, Stefan A1 - Akhtar, Naveed A1 - Brauch, Jennifer A1 - Breil, Marcus A1 - Davin, Edouard A1 - Ho-Hagemann, Ha T. M. A1 - Maisonnave, Eric A1 - Thürkow, Markus A1 - Will, Andreas T1 - Coupling of the regional climate model COSMO-CLM using OASIS3-MCT with regional ocean, land surface or global atmosphere model: description and performance T2 - Geoscientific Model Development N2 - We present the prototype of a regional climate system model based on the COSMO-CLM regional climate model coupled with several model components, analyze the performance of the couplings and present a strategy to find an optimum configuration with respect to computational costs and time to solution. The OASIS3-MCT coupler is used to couple COSMO-CLM with two land surface models (CLM and VEG3D), a regional ocean model for the Mediterranean Sea (NEMO-MED12), two ocean models for the North and Baltic Sea (NEMO-NORDIC and TRIMNP+CICE) and the atmospheric component of an earth system model (MPI-ESM). We present a unified OASIS3-MCT interface which handles all couplings in a similar way, minimizes the model source code modifications and describes the physics and numerics of the couplings. Furthermore, we discuss solutions for specific regional coupling problems like handling of different domains, multiple usage of MCT interpolation library and efficient exchange of 3D fields. A series of real-case simulations over Europe has been conducted and the computational performance of the couplings has been analyzed. The usage of the LUCIA tool of the OASIS3-MCT coupler enabled separation of the direct costs of: coupling, load imbalance and additional computations. The resulting limits for time to solution and costs are shown and the potential of further improvement of the computational efficiency is summarized for each coupling. It was found that the OASIS3-MCT coupler keeps the direct coupling costs of communication and horizontal interpolation small in comparison with the costs of the additional computations and load imbalance for all investigated couplings. For the first time this could be demonstrated for an exchange of approximately 450 2D fields per time step necessary for the atmosphere-atmosphere coupling between COSMO-CLM and MPI-ESM. A procedure for finding an optimum configuration for each of the couplings was developed considering the time to solution and costs of the simulations. The optimum configurations are presented for sequential and concurrent coupling layouts. The procedure applied can be regarded as independent on the specific coupling layout and coupling details. KW - Climate KW - Regional Climate Model KW - Regional Climate System Model KW - OASIS KW - Coupling KW - Performance KW - Parallelisation KW - Computational Efficiency KW - COSMO-CLM Y1 - 2016 U6 - https://doi.org/10.5194/gmd-2016-47 SN - 1991-9603 N1 - Discussion Paper VL - 47 SP - 1 EP - 61 ER - TY - GEN A1 - Will, Andreas A1 - Harlander, Uwe A1 - Metz, Werner T1 - Climatological relevance of leading seasonal singular vectors. Part I: Energy, enstrophy and spatio – temporal variability T2 - Meteorologische Zeitschrift N2 - Fast growing atmospheric Rossby wave trains (RWT modes) are solutions of a Singular Vector (SV) analysis of a damped barotropic vorticity equation for northern winter basic flows. Using 40 DJF basic flows RWT modes are found over four regions of the globe only. Their propagation paths are remarkably constant for development times up to 96 h, but spread for longer times. The RWT mode with the largest 4 day growth rate develops over the North-Pacific (NPAC) region for each of the observed DJF basic flows considered. This mode is referred to as NPAC-mode. The eigenvalues, which are the 4 day kinetic energy growth factors of the NPAC mode, range from 10 to 24 for nearly all of the basic flows. In some exceptional years they are close to 30. The NPAC modes with moderate growth factors could be shown to be approximate solutions of the nonlinear model equation. Hereto a new formulation of the advection term provided by the energy-vortex theory was used. It appears that the constancy of propagation paths and the mode's shapes, the large growth factors and the validity of the linearization assumption up to development times of 96h make the NPAC mode a candidate to explain substantial parts of large scale interannual atmospheric variability in the North Pacific region. KW - Meteorology KW - Rossby Waves KW - Extreme Event KW - Teleconnection KW - PNA KW - Enstrophy KW - Energy KW - Energy Vorticity Theory Y1 - 2006 U6 - https://doi.org/10.1127/0941-2948/2006/0145 SN - 1610-1227 VL - 15 IS - 4 SP - 1 EP - 10 ER - TY - GEN A1 - Früh, Barbara A1 - Will, Andreas A1 - Castro, Christopher T1 - Editorial: Recent developments in Regional Climate Modelling with COSMO‑CLM T2 - Meteorologische Zeitschrift N2 - The COSMO model in CLimate Model (COSMO-CLM or CCLM) is one of the most advanced Regional Climate Model with respect to its model dynamics, numeric, and physical parameterization options. It is widely used for climate research, climate mitigation and adaptation studies, as the model is specifically designed for simulation at a convective-permitting, meso-γ spatial resolution on the order of 1 km which: • has a well-tested range of applicability, encompassing operational numerical weather prediction (COSMO), regional climate modelling for retrospective and future projection (COSMO-CLM), idealised studies (ITC) and the dispersion of trace gases and aerosol (ART) on weather forecast to interannual time scales, • was successfully applied in several regions of the world, and especially widely within Europe • has widely been used to downscale the results of global climate models and, • is well documented. KW - COSMO-CLM KW - Regional Climate Model KW - Climate KW - Climate Change Y1 - 2016 U6 - https://doi.org/10.1127/metz/2016/0788 SN - 1610-1227 VL - 25 IS - 2 SP - 119 EP - 120 ER - TY - GEN A1 - Früh, Barbara A1 - Will, Andreas A1 - Castro, Christopher T1 - Editorial: Recent developments in Regional Climate 1 Modelling with COSMO-CLM, Part 2 T2 - Meteorologische Zeitschrift N2 - The special issue “Recent developments in Regional Climate Modelling with COSMO-CLM” aims to present 7 model developments of high relevance for the climate mode, model evaluation of new model versions and results 8 of model application down to local scale. In the first part, published in May 2016 (http://www.schweizerbart.de/ 9 papers/metz/list/25#issue2) eight articles are presented. In this second part further key aspects of high resolution 10 regional climate modelling are addressed in five articles. KW - COSMO-CLM KW - Regional Climate Model KW - Climate KW - Climate Change Y1 - 2016 U6 - https://doi.org/10.1127/metz/2016/0823 SN - 1610-1227 VL - 25 IS - 5 SP - S. 529 ER - TY - GEN A1 - Ghasemi, Abouzar A1 - Klein, Marten A1 - Will, Andreas A1 - Harlander, Uwe T1 - Mean flow generation by an intermittently unstable boundary layer over a sloping wall T2 - Journal of Fluid Mechanics Y1 - 2018 U6 - https://doi.org/10.1017/jfm.2018.552 SN - 1750-6859 IS - vol. 853 SP - 111 EP - 149 ER -