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ICON Non-Hydrostatic Dynamical Core

Idealized test case resultswith triangles and hexagons/pentagons as primal

grids

P. Rípodas1, A. Gassmann2, G. Zängl1, D. Reinert1 and H. Wan2

1Deutscher Wetterdienst, Offenbach (Main), Germany2Max Planck Institute for Meteorology, Hamburg, Germany

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ICON Non-Hydrostatic dynamical core (ICONAM) :

Triangles Hex/pent

R2B04 139 km 240 km

R2B05 69 km 120 km

R2B06 35 km 60 km

R2B07 17 km 30 km

We have two versions of ICONAM, with triangles and hexagons/pentagons as primal grids.

PDE's on the Sphere 2010

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IDEALIZED TEST CASES:

Jablonowski-Williamson steady state (JWs) Jablonowski-Williamson baroclinic wave (JWw) Mountain induced Rossby wave (MRW)

RESULTS FOR THE SURFACE PRESSURE (PS)

COMPARISON OF BOTH VERSIONS

GRID LEVELS:

R2B04 – R2B07 (up to 20 km)Time steps: 320s – 40s

MODEL SETTINGS:

Spring dynamics grid optimization, 4th-order diffusion (velocity field), 35 vertical levels (23.5 km)

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Geostrophically and hydrostatically balanced flow. Constant PS=1000 hPa

It is a steady state but dynamically unstable. Due to the irregular structure of the triangular grid, the zonal symmetry is lost after some days and low and high pressure systems are developing.

Jablonowski-Williamson steady state

Triangles, 17km, 40sPS at day 15999.23 – 1000.7 hPa

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The analytical solution is known-> errors can be calculated.The model is considered to be unable to maintain the balanced flow when the PS l2 error increases beyond a certain threshold level (0.5 hPa) (Lauritzen et al., 2009)

Jablonowski-Williamson steady state

A convergence is observed in the number of days that PS l2 is below 0.5 hPa.Very similar result for triangles and hex/pent.

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The initial conditions are the same as in JWs but with a perturbation in the zonal wind field → a baroclinic wave is triggered and reach its mature stage at day 9 We consider ECHAM (hydrostatic spectral general circulation model developed at MPI-M) as reference.

Jablonowski-Williamson baroclinic wave

ECHAM T799PS day 9

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Jablonowski-Williamson baroclinic wave

PS at day 9 at different resolutions

A phase delay is observed for coarse resolutions for triangles and hexagons

139 – 240 km

69 – 120 km

35 – 60 km

17 – 30 km

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Comparison to ECHAM5 T799: ICONAM-ECHAM PS differences at day 9

Jablonowski-Williamson baroclinic wave

triangles hexagons

R2B0717 km 30 km

A convergence of ICONAM is observed. The triangle and hexagon versions have very similar results.

R2B0635 km 60 km

PDE's on the Sphere 2010

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ICONAM hexagons - triangles differences (PS, day 9)

Jablonowski-Williamson baroclinic wave

Differences between triangles and hex/pent versions decrease with increasing resolution.

Differences between triangles and hex/pent versions are smaller than differences between ICONAM and ECHAM.

min -7.3 hPa max 5.9 hPa

R2B0569 – 120 km

min -3.4 hPa max 2.2 hPa

min -2.2 hPa max 1.8 hPa

R2B0717 – 30 km

R2B0635 – 60 km

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Smooth isothermal initial conditions that are a balanced analytic solution to the primitive equations. An idealized mountain triggers the evolution of a Rossby wave train.

Mountain induced Rossby Wave

ECHAM5 T799PS at day 15

PS at day 0

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Comparison to ECHAM5 T799 : ICONAM – ECHAM PS differences at day 15 → no convergence is observed

Mountain induced Rossby Wave

R2B06triangles hex/pent35 km 60 km

R2B07triangles hex/pent17 km 30 km

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Is the MRW ECHAM solution a good reference?

• The hydrostatic version of ICON (ICOHAM) shows a convergence to the ECHAM solution

• ICOHAM and ECHAM solutions use the same vertical level distribution, 31 vertical hybrid levels up to 0hPa but ICONAM uses 35 vertical height based hybrid levels up to 23.5 Km

• ICONAM with 40 levels (up to 35 Km) is closer to the ECHAM solution than ICONAM with 35 level (up to 23.5 Km)

→ ECHAM MRW solution can not be used as a reference for ICONAM because the solution depends sensitively on the depth of the simulation domain and on the reflection characteristics of the upper boundary

Mountain induced Rossby Wave

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ICONAM hexagons - triangles differences (PS, day15)

Mountain induced Rossby Wave

R2B04(139 – 240 km)

R2B05(69 – 120 km)

R2B06(35 – 60 km)

The largest differences are at the mountain position.

Differences between the two model versions decrease with resolution.

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Mountain induced Rossby Wave

hex-tri differencesR2B07

trianglesR2B0717 km

hex/pentR2B0730 km

At high resolution short wave-length differences between triangles and hex/pent versions and ECHAM appear.

ECHAMT799

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Conclusions

• Two versions of ICONAM (triangles and hex/pent) have been tested and compared using idealized test cases for resolutions up to 20 Km

• For the JW steady state test case both versions of the model have very similar results, a convergence is observed in the number of days for which the model maintains the initial balance of the flow.

• For the JW baroclinic wave test case, both versions of the model have very similar results. Differences between both versions decrease with increasing resolution. A convergence to an ECHAM solution used as reference is observed.

• For the MRW test case the ECHAM solution can not be used as reference. Differences between both versions decrease with increasing resolution.

• It is planned to implement the Held-Suarez test for the Non-Hydrostatic core.

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THANK YOU FOR YOUR ATTENTION

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