prague'03 / physics & its interfacing physics & its interfacing – the arome case...
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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!