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. Hydrostat. with no phys, ∆t=1h
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)
NH(2)-H(NH)
H(IFS)-ERA40

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. Anomaly correlation and rms error: 12 cases, Tl159L91NH
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 model hydrostatic test

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

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

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

22. Physics-Dynamics coupling Vertical 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. dt=3600s, sitra=100K
dt=1800s, sitra=50K
p-p_hyd
noise
dt=1800s, sitra=10K
Blows up!
dt=1800s, sitra=100K

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

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