ICON The next generation global model at DWD and MPI-M Current development status and selected results of idealized tests G

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ICON The next generation global model at DWD
and MPI-MCurrent development status
and selected results
of idealized testsGünther Zängl

and the ICON development team
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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).

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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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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
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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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Horizontal grid
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Horizontal grid
Primary (Delaunay, triangles) and dual grid
(Voronoi, hexagons/pentagons)
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Static mesh refinement (two-way nesting)
latitude-longitude windows
circular windows
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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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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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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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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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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,
  rhotheta and Exner function are rediagnosed

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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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• 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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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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Vertical velocity at 1.8 km AGL on day 10
70 km
140 km
140 km, nested
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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 RH70 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

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Temperature at lowest model level on day 14
70 km
35 km
70 km, nested
nest, 35 km
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QV (g/kg) at 1.8 km AGL on day 14
70 km
35 km
70 km, nested
nest, 35 km
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Accumulated precipitation (mm WE) after 14 days
70 km
35 km
70 km, nested
nest, 35 km
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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 30N/90E
• 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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Vorticity (1/s) at surface level on day 20
high-resolution (35 km)
nested (140-km domain)
coarse-resolution (140 km)
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Vorticity at surface level on day 20 (mountain
region)
high-resolution
nested (35-km domain)
coarse-resolution
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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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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, l8) are calculated after one
complete revolution for different resolutions
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Linear vs. quadratic reconstruction
quadratic
L1 0.53764E-01 L2 0.45283E-01

• 140 km res.
• c0.2
• flux limiter

linear
L1 0.61346E-01 L2 0.51185E-01
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Convergence rates
Quadratic reconstruction
Linear reconstruction
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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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• Thank you for your attention!