Prague'03 / Physics & its interfacing

Physics & its interfacing – the AROME case

J.-F. Geleyn & L. Gérard

I) Generalities

II) Challenges & likely problems

III) Prognostic convection for the 5-km target?

IV) The time-stepping issue

V) Summing-up

Prague'03 / Physics & its interfacing

Physics & its interfacing – generalities

• AROME will merge (for its 2.5-km version) the ALADIN-NH dynamics and the Meso-NH physics

• There will also exist a so-called ‘10-km version’ with a more flexible view of the physics (mix of «new» and «classical») especially for moist convection

• ALADIN-NH dynamics uses the Laprise system of equations while Meso-NH is an anelastic model. Both physics package are adapted to their dynamics, especially in the second case. How to intelligently merge differing concepts, especially for the time-stepping ?

• Convection is also a specific issue (half resolved / half parameterised) for the so-called ‘grey-zone’ (7-3km)

Prague'03 / Physics & its interfacing

Physics & its interfacing – challenges and likely problems

• Splitting the content of the Meso-NH physics (3D-turbulence, sophisticated microphysics, etc.) into Adaptative, Evolutive and Horizontal parts; making the H -part semi-Lagrangian-compatible

• Making the E-part and the current ALADIN interface compatible: equations and implementation

• Testing the new time-stepping concept; making the step from leap-frog to predictor-corrector => surprises ?

• Extending the merged concept to the 10km scale: reintroducing convection (and drag?) & testing the other schemes at long time steps

• Pursuing current tracks for a possible grey-zone solution

Prague'03 / Physics & its interfacing

Physics for grid meshes between 7 and 3 kmCurrent state in Aladin

Resolved precipitation: vertical velocity grid-scale saturation

Grid scale dependencySubgrid precipitation mass flux scheme for deep convection.vertical motion is channeled into a narrow updraughtClosure hypothesis: quasi equilibriumforcing by moisture convergence consumption by convection

diagnostic mass flux realised in 1 time stepConflict addressed by modulating the forcing

Prague'03 / Physics & its interfacing

Physics for grid meshes between 7 and 3 kmPrognostic Convection

auto extinction behaviour

Prague'03 / Physics & its interfacing

Physics for grid meshes between 7 and 3 kmPrognostic cloud condensates

Micro-physical package developed for the resolved precipitation

Prognostic suspended liquid water and iceContradicts various hypothesis of the subgrid scheme:

Immediate precipitation of all condensateNegligible updraught mesh fraction

Need of a more integrated solution

Prague'03 / Physics & its interfacing

Physics for grid meshes between 7 and 3 kmPrognostic cloud condensates

Prague'03 / Physics & its interfacing

Physics for grid meshes between 7 and 3 kmNew advances in Aladin

Environment moisture and condensate

Updraught micro physics downdraught

detrained material

Precipitation Environment of the updraught differs from large scale average,Detrained material does not mix instantaneouslyCAPE closure with characteristic time or prognostic closure by moisture convergence Downdraught's life cycle independent of that of the updraught

Prague'03 / Physics & its interfacing

Rough sketch of the AROME target time

marching scheme for physics (in P/C case)

A1 E

H

A2

Interp.

NL dyn.RHSof SI

Post Proc.

F

F

T

F

F

T

SI and other spectral comp.Spectral space

Standard grid

Origin points

m

Iterated part

Perhaps only at the end

?

Prague'03 / Physics & its interfacing

Comparison of AROME and Meso-NH 1D microphysical response to a constant forcing

(t=5s)

0

2000

4000

6000

8000

10000

0 0,0005 0,001 0,0015

(kg/kg)

alt

itu

de

(m

)

rc (arome)rr (arome)

ri (arome)rs (arome)

rg (arome)rc (meso-NH)

rr (meso-NH)ri (mésoNH)

rs (meso-NH)rg (méso-NH)

Prague'03 / Physics & its interfacing

Comparison of AROME 5s and 60s time-steps with a «centred» call to parameterisations

(‘t’)

0

2000

4000

6000

8000

10000

0 0,0005 0,001 0,0015

(kg/kg)

alt

itu

de

(m

)

rc (arome 5s)rr (arome 5s)ri (arome 5s)rs (arome 5s)rg (arome 5s)rc (arome 60s)rr (arome 60s)rg (arome 60s)ri (arome 60s)rs(arome 60s)

Prague'03 / Physics & its interfacing

Comparison of AROME 5s and 60s time-steps with a «forward» call to parameterisations

(‘t-dt’)

0

2000

4000

6000

8000

10000

0 0,0005 0,001 0,0015

(kg/kg)

alt

itu

de

(m

)rc (arome 5s)rr (arome 5s)ri (arome 5s)rs (arome 5s)rg (arome 5s)rc (arome 60s)rr (arome 60s)rg (arome 60s)ri (arome 60s)rs(arome 60s)

Prague'03 / Physics & its interfacing

Conclusions

This is a rather complex issue. There are even some side-issues that haven’t been mentioned here Work on the basic equations (not shown) is paramount if one wants good guidelines for long term solutionsWhen it comes to arranging the time step structure to be able to run with big time-steps, «NWP rule»The problem of convection at the grey-zone scale has not yet been fully attacked with the tools envisaged up to now in ALADINAll this work will require coordination, imagination and a bit of patience!