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 Problem with horizontal diffusion, which lead to noise and model failure in the stratosphere.

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.

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.

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

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

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

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

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

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!

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)

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

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

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

NH H(NH) diff

Anomaly correlation and rms error: 12 cases, Tl159L91 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

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

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

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

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

Physics-Dynamics coupling Vertical diffusion Two-layer problem depends on  !!!

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

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

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

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

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

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

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 …

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