1. 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
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2. 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;
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).
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3. 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
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4. 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 D hydrostatic model version
External: S. Reich, University of Potsdam: Time stepping schemes; R. Johanni: MPI-Parallelization
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5. 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
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6. Horizontal grid
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7. Horizontal grid
Primary (Delaunay, triangles) and dual grid (Voronoi, hexagons/pentagons)
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8. Static mesh refinement (two-way nesting)
latitude-longitude windows circular windows
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9. 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
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10. 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
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11. 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
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12. 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
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13. 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
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14. 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
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15. 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
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16. 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
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17. Vertical velocity at ~1.8 km AGL on day 10
140 km, nested
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18. 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 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
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19. Temperature at lowest model level on day 14
70 km
35 km
70 km, nested
nest, 35 km
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20. QV (g/kg) at 1.8 km AGL on day 14
70 km, nested
nest, 35 km
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21. Accumulated precipitation (mm WE) after 14 days
70 km
35 km
70 km, nested
nest, 35 km
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22. 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
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23. 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)
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24. Vorticity at surface level on day 20 (mountain region)
high-resolution
nested (35-km domain)
coarse-resolution
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25. 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
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26. 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
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27. Linear vs. quadratic reconstruction
L1 = E-01
L2 = E-01
140 km res.
c=0.2
flux limiter
linear
L1 = E-01
L2 = E-01
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28. Convergence rates Quadratic reconstruction Linear reconstruction
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29. 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, …
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30. Thank you for your attention!
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