ICON The next generation global model at DWD and MPI-M Current development status and selected results of idealized tests Günther Zängl and the ICON development team 15.11.2018 Zängl

The ICON-Project: main goals Centralize Know-how in the field of global modelling at DWD and the Max-Planck-Institute (MPI-M) in Hamburg. Develop a non-hydrostatic global model with static local zooming option (ICON: ICOsahedral Non-hydrostatic; http://www.icon.enes.org/). At DWD: Replace global model GME and regional model COSMO-EU by ICON with a high-resolution window over Europe. Establish a library of scale-adaptive physical parameterization schemes (to be used in ICON and COSMO-DE). At MPI-M: Use ICON as dynamical core of an Earth System Model (COSMOS); replace regional climate model REMO. Develop an ocean model based on ICON grid structures and operators. DWD and MPI-M: Contribute to operational seasonal prediction in the framework of the Multi-Model Seasonal Prediction System EURO-SIP at ECMWF). 15.11.2018 Zängl

Requirements for next generation global models Applicability on a wide range of scales in space and time → „seamless prediction“ (Static) mesh refinement and limited area model (LAM) option Scale adaptive physical parameterizations Conservation of mass (chemistry, convection resolving), energy? Scalability and efficiency on massively parallel computer systems with more than 10,000 cores Operators of at least 2nd order accuracy 15.11.2018 Zängl

Current project teams at DWD and MPI-M D. Majewski Project leader DWD (till 05/2010) G. Zängl Project leader DWD (since 06/2010) static local mesh refinement, parallelization, optimization, numerics H. Asensio external parameters M. Baldauf NH-equation set K. Fröhlich physics parameterizations D. Liermann post processing, preprocessing IFS2ICON D. Reinert advection schemes P. Ripodas test cases, power spectra B. Ritter physics parameterizations M. Köhler physics parameterizations U. Schättler software design MetBw T. Reinhardt physics parameterizations M. Giorgetta Project leader MPI-M M. Esch software maintenance A. Gassmann NH-equations, numerics P. Korn ocean model L. Kornblueh software design, hpc L. Linardakis parallelization, grid generators S. Lorenz ocean model C. Mosley regionalization T. Raddatz external parameters F. Rauser adjoint version of the SWM W. Sauf Automated testing (Buildbot) U. Schulzweida external post processing (CDO) H. Wan 3D hydrostatic model version External: S. Reich, University of Potsdam: Time stepping schemes; R. Johanni: MPI-Parallelization 15.11.2018 Zängl

Present development status Consolidated version of hydrostatic dynamical core with option to switch between triangles and hexagons as primal grid Nonhydrostatic dynamical core for triangles and hexagons; basic testing and efficiency optimization finished Two-way nesting for triangles as primal grid, capability for multiple nests per nesting level; one-way nesting mode and limited-area mode are also available Positive-definite tracer advection scheme (Miura) with 2nd-order accuracy, 3rd-order PPM for vertical advection; 3rd-order horizontal in testing/optimization phase OpenMP and MPI parallelization, blocking (selectable inner loop length) for optimal vectorization or cache use (depending on architecture) Technical preparations for physics coupling available; so far, grid-scale cloud microphysics, saturation adjustment and convection are included Dynamical core of ocean model currently under revision 15.11.2018 Zängl

Horizontal grid 15.11.2018 Zängl

Horizontal grid Primary (Delaunay, triangles) and dual grid (Voronoi, hexagons/pentagons) 15.11.2018 Zängl

Static mesh refinement (two-way nesting) latitude-longitude windows circular windows 15.11.2018 Zängl

Grid structure (schematic view) Triangles are used as primal cells Mass points are in the circumcenter Velocity is defined at the edge midpoints Red cells refer to refined domain Boundary interpolation is needed from parent to child mass points and velocity points 15.11.2018 Zängl

Nonhydrostatic equation system (triangular version) vn,w: normal/vertical velocity component K: horizontal kinetic energy : vertical vorticity component : density v: Virtual potential temperature : Exner function 15.11.2018 Zängl

Numerical implementation Momentum equation: Rotational form for horizontal momentum advection (2D Lamb transformation), advective form for vertical advection, conservative advective form for vertical wind equation Flux form for continuity equation and thermodynamic equation; Miura scheme (centered differences) for horizontal (vertical) flux reconstruction implicit treatment of vertically propagating sound waves, but explicit time-integration in the horizontal (at sound wave time step; not split-explicit) Two-time-level Adams-Bashforth-Moulton time stepping scheme Mass conservation and tracer mass consistency 15.11.2018 Zängl

Implementation of two-way nesting Flow sequence: 1 time step in parent domain, interpolation of lateral boundary fields/tendencies, 2 time steps in refined domain, feedback Boundary interpolation of scalars (dynamical and tracers): RBF reconstruction of 2D gradient at cell center Linear extrapolation of full fields and tendencies to child cell points Boundary interpolation of velocity tendencies RBF reconstruction of 2D vector at vertices Use to extrapolated to child edges lying on parent edge Direct RBF reconstruction of velocity tendencies at inner child edges Weak second-order boundary diffusion for velocity 15.11.2018 Zängl

Implementation of two-way nesting Feedback: Dynamical variables: bilinear interpolation of time increments from child cells / main child edges to parent cells / edges Additive mass-conservation correction for density Tracers: bilinear interpolation of full fields from child cells to parent cells, multiplicative mass-conservation correction Bilinear feedback is inverse operation of gradient-based interpolation For numerical stability, velocity feedback overlaps by one edge row with the interpolation zone Density and (virtual) potential temperature are used for boundary interpolation / feedback, rho*theta and Exner function are rediagnosed 15.11.2018 Zängl

One-way nesting and other options One-way nesting option: Feedback is turned off, but Davies nudging is performed near the nest boundaries (width and relaxation coefficients can be chosen via namelist variables) One-way and two-way nested grids can be arbitrarily combined An arbitrary number of nested domains per nesting level is allowed Multiple nested domains at the same nesting level can be combined into a logical domain to reduce parallelization overhead (exception: one-way and two-way nested grids have to be assigned to different logical domains) An option to run computationally expensive physics parameterizations at reduced resolution is in preparation 15.11.2018 Zängl

Idealized tests Purpose: Validation of correctness of numerical implementation, assessment of convergence properties and numerical stability Jablonowski-Williamson baroclinic wave test Modified Jablonowski-Williamson baroclinic wave test with moisture and cloud microphysics parameterization Mountain-induced Rossby wave test Tracer advection test: Convergence study for advection of a tracer cloud in quasi-uniform flow 15.11.2018 Zängl

Development of baroclinic waves Baroclinic wave case of Jablonowski-Williamson (2008) test suite Nonhydrostatic dynamical core Basic state: geostrophically and hydrostatically balanced flow with very strong baroclinicity; small initial perturbation in wind field Disturbance evolves very slowly during the first 6 days, explosive cyclogenesis starts around day 8 Grid resolutions 140 km and 70 km, 35 vertical levels Results are shown after 10 days location of nest 15.11.2018 Zängl

Vertical velocity at ~1.8 km AGL on day 10 140 km, nested 15.11.2018 Zängl

Baroclinic wave test with moisture Modified baroclinic wave case of Jablonowski-Williamson (2008) test suite with moisture and Seifert-Beheng (2001) cloud microphysics parameterization (one-moment version; QC, QI, QR, QS) Initial moisture field: RH=70% below 700 hPa, 60% between 500 and 700 hPa, 25% above 500 hPa; QV max. 17.5 g/kg to limit convective instability in tropics Transport schemes for moisture variables: Horizontal: Miura 2nd order with flux limiter Vertical: 3rd-order PPM with slope limiter Grid resolutions 70 km and 35 km, 35 vertical levels Results are shown after 14 days 15.11.2018 Zängl

Temperature at lowest model level on day 14 70 km 35 km 70 km, nested nest, 35 km 15.11.2018 Zängl

QV (g/kg) at 1.8 km AGL on day 14 70 km, nested nest, 35 km 15.11.2018 Zängl

Accumulated precipitation (mm WE) after 14 days 70 km 35 km 70 km, nested nest, 35 km 15.11.2018 Zängl

Rossby wave generation by a large-scale mountain Mountain-induced Rossby-wave case of Jablonowski-Williamson test suite Nonhydrostatic dynamical core Basic state: isothermal atmosphere, zonal flow with max. 20 m/s Standard setup with 2000-m high circular mountain at 30°N/90°E “High-resolution” runs: 35 km mesh size; 35 levels “Coarse-resolution” runs: 140 km “Nested” runs: 140 km globally, double nesting to 35 km over mountain Results are shown after 20 days 15.11.2018 Zängl

Vorticity (1/s) at surface level on day 20 coarse-resolution (140 km) high-resolution (35 km) coarse-resolution (140 km) nested (140-km domain) 15.11.2018 Zängl

Vorticity at surface level on day 20 (mountain region) high-resolution nested (35-km domain) coarse-resolution 15.11.2018 Zängl

Horizontal wind at surface level (barbs), vertical wind at 2 Horizontal wind at surface level (barbs), vertical wind at 2.5 km AGL on day 20 (colours) high-resolution nested (35-km domain) coarse-resolution 15.11.2018 Zängl

Solid body rotation test case Uniform flow along northeast direction Initial scalar field is a cosine bell centered at the equator After 12 days of model integration, cosine bell reaches its initial position Analytic solution at every time step = initial condition Error norms (l1, l2, l∞) are calculated after one complete revolution for different resolutions 15.11.2018 Zängl

Linear vs. quadratic reconstruction L1 = 0.53764E-01 L2 = 0.45283E-01 140 km res. c=0.2 flux limiter linear L1 = 0.61346E-01 L2 = 0.51185E-01 15.11.2018 Zängl

Convergence rates Quadratic reconstruction Linear reconstruction 15.11.2018 Zängl

Summary The nonhydrostatic dynamical core has been thoroughly tested and compares well with reference solutions from a spectral model; it appears to have good stability properties over steep topography Two-way nesting also works numerically stable over long times (tested for integration times up to 100 days) and exhibits only very small disturbances along the nest boundaries State-of-the-art transport schemes have been implemented for tracer advection; further investigations will be made to determine the optimal compromise between accuracy and computational cost Now the focus will be directed towards completing physics coupling, incorporating real external parameter data, I/O parallelization, using real NWP analysis data as input, data assimilation, … 15.11.2018 Zängl

Thank you for your attention! 15.11.2018 Zängl