The Grey Zone Project
Pier Siebesma
Grey Zone committee: Andy Brown, Jeanette Onvlee, Martin Miller, Pier Siebesma
1.
Introduction on the Grey Zone
2.
A proposal
3.
Discussion and Next Steps
WGNE Boulder
(from a parameterizational point of view)
(thanks to Paul Field and Adrian Hill (Met Office))
The Grey Zone Project
1
Motivation
• Increased use of (operational) models in the “grey zone”
(Dx = 1 ~10km)
•Models operating in this resolution range resolve some of the “aggregation of
convective cells” but certainly no individual convective cells.
•This leads to the “wrong” perception that these “grey-zone” models, when operating
without (deep) convection parameterizations, can realistically represent turbulent
fluxes of heat, moisture and momentum.
•Hence there is a urgent need of a systematic analysis of the behavior of NWP models
operating in the “grey-zone”:
“The Grey Zone Project”
WGNE Boulder
The Grey Zone Project
2
Some Background
“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
WGNE Boulder
The Grey Zone Project
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“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
Prime Example: Cloud schemes
WGNE Boulder
The Grey Zone Project
4
“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
Prime Example: Subgrid Cloud Fraction
qsat
qt
WGNE Boulder
The Grey Zone Project
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“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
Prime Example: subgrid cloud fraction
qsat(T)
.
(T,qt)
qt
T
WGNE Boulder
The Grey Zone Project
6
“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
Prime Example: subgrid cloud fraction
qsat(T)
.
(T,qt)
qt
__________ ____
Cloud fraction:
WGNE Boulder
ac  H qt  qs   H qt  qs 
T
The Grey Zone Project
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“Many of the parameterization issues (especially clouds and convection) evolve
around finding the subgrid (co)variances of w, T and q”
Prime Example: subgrid cloud fraction
qsat(T)
.
(T,qt)
qt
__________ ____
Cloud fraction:
ac  H qt  qs   H qt  qs 
T
ac   H (qt  qs ) P(qt , l )dqt d l
WGNE Boulder
The Grey Zone Project
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•This biased errors slowly go away if resolution increases:
__________ ____
x 0
ac  H qt  qs  D
 H qt  qs 
•Typically allowed for Dx~100m, i.e. at the LES scale
•So for all models operating at a coarser resolution additional information
about the underlying Probability Density Function (pdf) is required of
temperature, humidity (and vertical velocity).
P(T , qt , w)
•Or, as a good approximation, the variances and covariances:
q2 ,  2 , w2 , wq, w , q ,
As a function of the used resolution!!
WGNE Boulder
The Grey Zone Project
9
Example:a posteriori coarse graining
•Use a reference (LES) model that resolves the desired phenomenum ( Dx << lphen)
•Has a domain size much larger than the desired phenomenum
•Coarse grain the (co)variances across these scales
L
  (l )   
2
2

l
l
  
L
subgrid
WGNE Boulder
l  Dx, L
( L >> lphen)

L 2
L
resolved
The Grey Zone Project
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Methodology:
•Use a reference (LES) model that resolves the desired phenomenum ( Dx << lphen)
•Has a domain size much larger than the desired phenomenum
•Coarse grain the (co)variances across these scales

2
L
 
2

l
l
  

L 2
L
L
subgrid

2
L
 
2
l  Dx, L
( L >> lphen)
resolved
L
 0
l=L
L

2
L

 0   

L 2
l = Dx
L
WGNE Boulder
The Grey Zone Project
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Applied to shallow cumulus convection:
l
q (l )
2
L
Subgrid
contribution
Subgrid contribution starts
to shrink if l~ 5 lphen~5km
WGNE Boulder
l
The Grey Zone Project
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Similar analysis for fluxes (heat flux)

w l
Grey zone sets in at smaller scales
Due to the fact that the w-spectrum peaks at smaller scales
WGNE Boulder
The Grey Zone Project
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Not completely unrelated to stochastic physics………..
subgrid
resolved
l=1.6km
l=6.4km
l=12.8km
Moisture turbulent flux
WGNE Boulder
The Grey Zone Project
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Stratocumulus generates larger horizontal scales…….
How large is large enough?
De Roode et al: JAS 61 p403 2004
WGNE Boulder
The Grey Zone Project
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q
2
l
L
Subgrid
contribution
q
2
l
L
WGNE Boulder
The Grey Zone Project
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q
2
l
L
Subgrid
contribution
Now the grey zone sets in at 10
km or more.
WGNE Boulder
The Grey Zone Project
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Schematics of the grey zone (including the stochastic arena)
Remarks:
1)
The grey zone depends on the size of the considered process (convection
(shallow or deep) , clouds (stratocumulus, shallow or deep)
2)
The stochastic arena is stretching out a factor of 5 to 10 further.
Deterministic
Stochastic Arena
(statistical)
Grey zone
variance,
resolved
total
Arena
parametrized
flux
Lphen
10~50 Lphen
Horizontal resolution (Dx)
WGNE Boulder
The Grey Zone Project
18
Proposal (from WGNE 2010 meeting)
• Project driven by a few expensive experiments (controls) on a large domain at a
ultra-high resolution (Dx=100~500m) (~2000x2000x200 grid points).
•Coarse grain the output and diagnostics (fluxes etc) at resolutions of 0.5, 1, 2, 4, 8,
16, 32 km. (a posteriori coarse graining: COARSE)
•Repeat CONTROLS with o.5 1km, 2km, 4km, 8km, etc without convective
parametrizations etc (a priori coarse graining: NOPARAMS)
•Run (coarse-grain) resolutions say 0.5, 1km, 2km, 4km and 8km with convection
parametrizations (a priori coarse graining: PARAMS)
•Preference especially from the mesoscale community for a cold air outbreak
WGNE Boulder
The Grey Zone Project
19
Aims
• Show how faithfully fluxes, variances, cloud structures, etc can be represented by
comparing COARSE, NOPARAMS and PARAMS depending on all aspects of set-ups.
• Guide improvements in current schemes especially at these resolutions - essential
for future progress
• Gain some insight and understanding of what can be achieved without
parametrizations
• Clarify what cannot/should not be done without parametrization also!!
Strong Support from both the international NWP and Climate
community
WGNE Boulder
The Grey Zone Project
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CONSTRAIN – proposal for cold
air outbreak case
(thanks to Paul Field & Adrian Hill, Met Office)
CONSTRAIN
-flights over the North Atlantic from January 12 to 31 2010.
- The proposed case is based in observations and NWP data
from January 31st 2010.
• Observations show that
this day is characterised by
northerly flow and
stratocumulus clouds at 65N
-10W. As air advects over
warmer seas the Sc
transitions to mixed-phase
cumulus clouds at around
60N, prior to reaching land
The Case (1)
• The Mesoscale Community is interested to
start with an extra-tropical case
• Cold-air outbreaks are of general interest
for various communities
• Proposal: “Constrain” cold-air outbreak
experiment
31 January 2010
• Participation of global models,
mesoscale models but also from LES
models !!
•Domain of interest: 1500X1000 km
•Quick Transition : ~ 12 hours
The Case (2)
4 Different Flavours
1.
Global Simulations (at the highest
possible resolution up to 5 km)
2.
Mesoscale Models (Eulerian)
At various resolutions (up to ?)
3.
Mesoscale Models (Lagrangian)
Idealized with periodic BC
highest resolution (~100m)
4.
LES models
(Lagrangian)
(in the same set up as 3)
LAM simulation
Quasi-lagrangian trajectory
Low cloud fraction
Quasi-lagrangian timeseries
start point 65 N -10 W, 0 UTC
Initial Proposal for LES/Mesoscale Langrangian
set-up
• x,y domain = 250 X 250 km (how large is large enough? )
•dx, dy ~ 250 m
• z domain = 5 km
•dz = 20 m between surface up to 100m at 5000m
• The case is initialised with total water, potential temperature
based on output from the NWP simulation
Forcing
Surface forcing
x hours spinup with fixed
SST
Subsidence
Interest on participation on the Grey Zone Project
global
MetO
Meso
Meso
Operational
idealised
MetO globa
MetO meso
MetO meso
Model
model
model
LES
contacts
MOLEM
Paul Field
Adrian Lock
Andy Brown
Meteo
Arpege
France
AROME
AROME
MesoNH
MesoNH (p)
MesoNH
Bouysel
Eric Bazile
Fleur Couvreux
DWD
ICON
(MPI-H)
COSMO-EU
COSMO-EU
COSMO-DE
COSMO-DE
UCLA-LES
Martin Kohler
Axel Seifert
Verena Grutzun
Met Service
Canadian
Canada
LAM
Canadian
LES
Vaillancourt
Jason Milbrandt
Aytron Zadra
Stephan Belair
NCAR
ECMWF
KNMI
WRF
WRF (p)
IFS (p)
WRF(p)
Jim Dudhia
Anton Beljaars
HARMONIE
HARMONIE (p)
Wim de Rooy
Discussion Points (1)
• Global Model runs:
–
The cloud types under consideration are probably to small to be able to penetrate into the
grey zone (at least for the turbulent fluxes)
–
So for these models it is more a classic parameterization excerise
–
Still relevant enough?
–
Look for (larger) cloud types for which the grey zone issues are more relevant?
–
MJO case , now? In a later phase?
• Eulerian (operational) Mesoscale Model runs
–
Can some of these models reach the fully resolved mode “LES (~250m) implying a domain
size of 1000X1500 km ? (4000X6000 grid points)
–
Will each mesoscale model run with the same lateral boundary conditions?
Discussion Points (2)
• Lagrangian runs (LES and Mesoscale)
– How large is large enough? (250X250km)
– How long do we need to spin up in order to let mesoscale structures form
• How much do we constrain/simplify the case in the Lagrangian
mode:
– simplify subsidence fields?
– Prescribe drag coefficients for the surface fluxes?
– Nudge winds?
Time Line and Organisation
– october/december : testruns with at least 2 LES (MOLEM, DALES)
– Release January 2012
Organisation: different case leaders for the 4 flavours ( a la TWP-ICE)?
MPI has shown interest (Verena Grutzun)
Meto?
Others?