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Non-hydrostatic IFS at ECMWF

Non-hydrostatic IFS at ECMWF. Mariano Hortal, Deborah Salmond, Agathe Untch, and Nils Wedi. Topics. NH-IFS stability physics-dynamics coupling NH-IFS climate and forecast performance Tracer transport: physics-dynamics coupling idealized flow experiments. NH-IFS.

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Non-hydrostatic IFS at ECMWF

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  1. Non-hydrostatic IFS at ECMWF Mariano Hortal, Deborah Salmond, Agathe Untch, and Nils Wedi

  2. Topics • NH-IFS stability • physics-dynamics coupling • NH-IFS climate and forecast performance • Tracer transport: physics-dynamics coupling • idealized flow experiments

  3. NH-IFS • Problem with horizontal diffusion, which lead to noise and model failure in the stratosphere.

  4. Problem with horizontal diffusion Inconsistency in setup of horizontal diffusion in NH at ECMWF: diffusion applied on horizontal divergence and the two new non-hydrostatic variables was different. This did not show up as a problem in CY30R1, however in CY31R1 it results in noise in the horizontal divergence: When the same diffusion is applied on the NH variables as on horizontal divergence this noise does not develop.

  5. Model failure when coupled to the physics • Using large time-steps we encountered problems with “bull’s eyes” in the temperature field near the surface in areas with steep orographic gradients which lead to model failure.

  6. 2. Problem with temperature over steep orography NH run at T159L60, ∆t=1h, NSITER=1 Temperature at level 59 after 27h

  7. NH with NSITER=2, ∆t=1h Hydrostatic run, ∆t=1h (with physics)

  8. NH with NSITER=1, ∆t=1h Hydrostat. with no phys, ∆t=1h (no physics)

  9. NH with NSITER=1, ∆t=1h Hydrostat. with no phys, ∆t=1h LVERAVE_HLUV=FALSE (no physics)

  10. 2. Problem with temperature over steep orography NH run at T159L91, NSITER=1, NEPHYS=3, Temperature at level 90 after 168h ∆t=0.5h ∆t=1h

  11. Summary: near surface sensitivities in the vicinity of steep orography • Decrease the time-step • Switching off the averaging of surface winds • Change the number of iterations • Sensitivity to pointwise large surface wind accelerations (implicit convection scheme formulation) LVERAVE_HLUV=F NSITER=2 works best!

  12. Physics – Dynamics coupling • Development of 2 options to call physics: • Call physics only in the last corrector step of the ICI scheme (adiabatic predictor steps) (NEPHYS=3), NH(3) • Call physics in the predictor step and use these physical tendencies in each subsequent corrector step (NEPHYS=2), NH(2)

  13. NH-IFS with physics • Does the model climate of the NH version of IFS differ from the climate of the hydrostatic version for a Tl159L91 resolution ? • 3 member ensemble • 1 year • daily SST forcing

  14. zonal-mean zonal wind NH(3) – H(NH) H(NH) – H(IFS) H(IFS)-ERA40 NH(2)-H(NH)

  15. zonal-mean zonal temperature NH(3) – H(NH) H(NH) – H(IFS) NH(2)-H(NH) H(IFS)-ERA40

  16. NH H(NH) diff

  17. NH H(NH) H 500hPa Z, Northern Hemisphere 500hPa Z, Southern Hemisphere 500hPa T, Tropics Anomaly correlation and rms error: 12 cases, Tl159L91 CPU time factor: H=1; H(NH)=1.5; NH=2; H(NH) and NH used NSITER=2

  18. Physics – Dynamics coupling • 2 separate calls to vertical diffusion scheme, before and after calls to cloud and convection to test possibility for a better near surface balance in the last corrector step of nonhydrostatic modelhydrostatic test

  19. Physics – Dynamics coupling 1 call to vdfmain 2 calls to vdfmain

  20. Anton Beljaars Physics-Dynamics couplingVertical diffusion • Negative tracer concentrations noticed despite a quasi-monotone advection scheme

  21. Physics-Dynamics couplingVertical diffusion (Kalnay and Kanamitsu, 1988) Single-layer problem

  22. Physics-Dynamics couplingVertical diffusion Two-layer problem depends on  !!!

  23. (D+P)t (D+P)t+t  = 1.5 Dt+t  = 1 Anton Beljaars

  24. Idealized flow past a mountain on the sphere • Initial zonal flow, isothermal atmosphere, no physics • Hydrostatic mountain NL/U >>1 • Non-hydrostatic mountain NL/U ~ 1 • Froude number Nh/U ~1

  25. Hydrostatic model Tl799L91, NL/U ~ 900 Hydrostatic regime Non-hydrostatic model Horizontal divergence D

  26. Tl159L91, NL/U ~ 2.5 Near non-hydrostatic regime Horizontal divergence D hydrostatic model non-hydrostatic model

  27. Blows up! p-p_hyd dt=1800s, sitra=10K dt=1800s, sitra=50K dt=3600s, sitra=100K dt=1800s, sitra=100K noise

  28. dt=1800s, sitra=150K dt=1800s, sitra=200K Blows up! dt=1800s, sitra=100K dt=1800s, sitra=350K

  29. Next steps • Further investigate the physics-dynamics interaction with NH-IFS • Test NH-IFS in higher resolution • Idealized tests in the NH regime on the sphere • Improve the scores …

  30. dt=3600s, p-p_hyd dt=3600s, horiz. divergence dt=1800s, p-p_hyd dt=1800s, horiz. divergence

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