lidar observations constraint for cirrus modelisation in large eddy simulations
DESCRIPTION
LIDAR OBSERVATIONS CONSTRAINT FOR CIRRUS MODELISATION IN Large Eddy Simulations. O. Thouron, V. Giraud (LOA - Lille) H. Chepfer, V. Noël(LMD - Palaiseau) / J. Pelon (SA - Paris) / J-L Redelsperger (CNRM - Toulouse). Introduction. - PowerPoint PPT PresentationTRANSCRIPT
LIDAR OBSERVATIONS CONSTRAINT
FOR CIRRUS MODELISATION
IN Large Eddy Simulations
O. Thouron, V. Giraud (LOA - Lille)
H. Chepfer, V. Noël(LMD - Palaiseau) / J. Pelon (SA - Paris) / J-L Redelsperger (CNRM - Toulouse)
The reason that cirrus clouds are not well understood is that many atmospheric processes affect their development, structure and evolution:
• on the locale scale : radiation, aerosol properties, gravity waves, shear instability, latent heating, microphysical properties, ….
• On a larger scale : interaction with jet streams, interaction with planetary-scale waves, passing pressure systems, large scale lifting or descent ...
Successful parameterization of cirrus clouds needs to be based on an understanding of all the processes and their interactions.
Introduction
How active remote sensing bring the signatures of processes and their interactions at local scales?
How active remote sensing may be convenient to constrain physical parameterizations in Cloud Resolving Models?
Introduction
- strategy
- model used to make LES simulations
- cirrus cloud generation
- sensitivity study: microphysical processes
- conclusion
- perspective
Plan
Aircraft + ECMWF+radio sonde data
Synthetic Observations
fields 2/3D
Active Observations
Passive Observations
Radiatif transfer calculation
Microphysical Scheme
MESO-NH
Observations
Modelisation
Comparison
Idealized case
Sensibility Study of the lidar
to the microphysical processes
Strategy
Use the French atmospheric simulated system meso-NH
Run in 1, 2 or 3 dimensions
Non hydrostatic meso scale model
Bulk microphysical scheme
Designed to study convective cloud or precipitating cloud
It was necessary: - to adapt the microphysical scheme to simulate cirrus
- to prognostic ice number concentration
to be abble to calculate synthetic observations
The model
- spherical particles
- size distribution : gamma modified
First type SP :
Second type NSP :
- non spherical particles
(columns or plates)
- size distribution : gamma modified
Microphysical scheme
Sedimentation
AggregationTransformation
Water Vapor
SP
NSP
Sublimation
Sedimentation
Nucleation
Deposition
Resolution domain
0
2000
4000
6000
8000
10000
12000
14000
16000
0 1 2 3 4 5 6 7 8 9 10 11 12
Height (m)
Ho
rizo
nta
l E
xten
t (k
m)
50 m
100 m
Sponge zone
Limit Conditions: Cyclic2D simulations
Resolution domain
Cirrus clouds are generated in a similar way to the GEWEX Cloud Systems Study (GCSS) cirrus cloud intercomparison (Starr et al. 2000)
Cloud Forcing: - cooling equivalent to ascent at 3 cm/s- between 7 and 10 km
Turbulent structure: - initialized by artificial heat perturbation (+/- 0.01K) between 8 and 9 km
Cirrus cloud generation
Duration : 5 hours
Radiation turned off
Base run:
Nu=1000 l-3
Ri*=20mg.m-3
Adjustment on 100%
Velocity: Starr (1985)
nucleation:
Deposition
Sedimentation
Meyer: - Supersaturation ratio with respect to ice
- Ice nuclei number: Nu
Transformation
Depend on the primary ice water content threshold
Depend on the sursaturation in the cirrus
Depend on velocity-mass relation parameters c and d:dcDDV )(
The sensitivity study
Base run results after 4 hours: Direct output
Base run results after 4 hours: Deducted output
Sedimentation
AggregationTransformat
Water Vapor
SP
NSP
Sublimation
Sedimentation
Nucleation
Deposition
Sensitivity study: Ice nuclei numberIce primary backscattering(km-1) Ice cristal backscattering(km-1)Total backscattering(km-1) Depolarisation
1 h
2 h
4 h
500 l-1
1000 l-1
1500 l-1
Sedimentation
AggregationTransformat
Water Vapor
SP
NSP
Sublimation
Sedimentation
Nucleation
Deposition
Sensitivity study: the primary ice water content threshold
Mean backscatterring Depolarisation
1 h
2 h
4 h
10 mg.m-3
20 mg.m-3
30mg.m-3
Water Vapor
Sedimentation
AggregationTransformat
SP
NSP
Sublimation
Sedimentation
Nucleation
Deposition
Sensitivity study: Fall speed velocity
Fall speed velocity
0
10
20
30
40
50
60
0 100 200 300 400 500
diameter en micro m
Sp
ee
d (
cm
/s)
Primary ice
Ice cristal: Star(1985)
Small ice cristal:Heymsfield (2001)
Larger ice cristal:Heymsfiel (2001)
DepolarisationMean backscatterring
1h
2h
4h
0
10
20
30
40
50
60
0 100 200 300 400 500
Primary ice
Ice cristal: Star(1985)
Small ice cristal:Heymsfield (2001)
Larger ice cristal:Heymsfiel (2001)
mg.m-3
Sensitivity study: Deposition
Water Vapor
Sedimentation
AggregationTransformat
SP
NSP
Sublimation
Sedimentation
Nucleation
Deposition
Mean backscatterring Depolarisation
1h
2h
4h
50%
100%
80%
DepolarisationLidar
BackscaterringLidar
BackscaterringDepolarisation
Nucleation Transformation Fall speed
velocityDéposition
Sublimation
v
v v
v
v
v
v
Conclusion
v
Perspectives•Structure analysis: FFT
•Radar data
•Used of real case in order to constrain the model