Scientific Advisory Committee Meeting, November 25-26, 2002 Large-Eddy Simulation Andreas Chlond...
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Transcript of Scientific Advisory Committee Meeting, November 25-26, 2002 Large-Eddy Simulation Andreas Chlond...
Scientific Advisory Committee Meeting, November 25-26, 2002
Large-Eddy Simulation
Andreas ChlondDepartment Climate Processes
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Outline
• Motivation
• LES-Tool
• Strategy
• Examples of LESs LES of cold air outbreaks
LES of the stratocumulus topped boundary layer
LES of shallow cumulus
• How can LES be used to improve Large-Scale Models?
• Conclusions
• Outlook
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Motivation
• Sub-grid scale processes need to be parameterized in GCMs and CTMs
Diurnal variation of LWP (FIRE)
• Boundary layer structure is not well represented
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Boundary layer processes
•provides surface-boundary conditions •interacts with the large-scale flow•interacts with other parameterization
schemes
A realistic representation of the boundary layer is an essential ingredient of climate models because
Scientific question:Which physical processes determine the state of the cloud-topped boundary layer?•cloud cover•entrainment•organizationObjective:•evaluate and improve methods of representing shallow cloud systems in GCMs (GCSS WG1)
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Large-Eddy Simulation Concept:• only the important part of the turbulent motions is calculated• the net effect of the small eddies is modelled by a subfilter model
•„dissipate“ energy•eddy-viscosity-mixing-length model
Strengths:• excellent tool for studying turbulence• generate database of PBL regimes
4
13 )( L
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Strategy
Observations
Large-Eddy Simulations
Parameterizations
(SCM)
Climate Model(GCM)
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Examples of LESs
•LES of cold air outbreaks
•LES of the stratocumulus topped boundary
layer
•LES of shallow cumulus
Flow regimes:
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of cold air outbreaks
Goals:
• Pattern transition
• Scale broadening
Strategy:
• Lagrangian simulation with an adaptive grid
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of cold air outbreaks
Main result: Cell broadening of atmospheric MCC is caused by latent heating/cooling due condensation/evaporation and due to radiative cloud top cooling
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of stratocumulus
•part of the general circulation
•important modulators of the earth's radiation budget
•of importance to our understanding of the physics of the atmosphere
Marine stratocumulus clouds are
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of stratocumulus (ASTEX)
Goals and objectives:
•How well can turbulence and cloud structure be reproduced by LES?
•Investigation of the statistical significance of LES-derived data products.
•Sensitivity analysis with respect to the treatment of subgrid-scale processes and microphysical processes
•Examination of the sensitivity of our LES results with respect to various external, environmental conditions
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of stratocumulus (ASTEX)
• Representation of precipitation is difficult
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of stratocumulus (FIRE)
Challenge: diurnal cycleWhich factors determine:• cloud cover, LWP, BL-height • entrainment rate• turbulence structure• microphysical properties
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES: Diurnal variation of LWP (FIRE)
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES: Sensitivities with respect to inversion properties (FIRE)
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of shallow cumulus
•determines the vertical thermo-dynamic structure
•is part of the large-scale circulation
•is part of the feeder system for deep convection
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of shallow cumulus (ATEX)
Question:
•Are results obtained for BOMEX case still valid under conditions of high cloud cover?
Difference:
•Existence of a layer of high relative humidity near the inversion
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES of shallow cumulus (ATEX)
Results:
•Many elements of the turbulent structure are robust
•Representation of stratiform cloud amount is sensitive
•Part of this sensitivity is due to a physically realistic positive radiative feedback
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
How can LES be used to improve Large-Scale Models?
•advance the understanding of the physical processes
•evaluate and improve methods of representing shallow clouds
•produce comprehensive 4-D data sets using LESs
•use of LES data sets to investigate deficiencies in GCMs using the Single Column Model (SCM) version as a test bed
•correct and improve parameterizations in ECHAM
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Diurnal cycle of shallow cumulus over land (ARM case)
Questions: • Do models reproduce correct timing?• Do scaling laws still apply? • How is sub-cloud layer affected by cu?
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
LES vs SCM: Diurnal variation of cloud cover (ARM case)
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Conclusions
•LES the best technique we have today for studying turbulence and cloud processes in the boundary layer
SUBROUTINE vdiff (kidia,kfdia,klon,klp2,ktdia,klev,klev, & & paclcm,paphm1,papm1,pgeom1,pum1,pvm1,pxm1)
! Description:!-- Computation of the exchange coefficientsIMPLICIT NONE! Scalar arguments with intent(In):INTEGER, INTENT (IN) :: kfdia, kidia, klev, klevm1, klevp1,& & klp2, ktdia, ktrac
DO jl = kidia, kfdia zdu2 = MAX(zepdu2,pum1(jl,klev)**2+pvm1(jl,klev)**2) zqmitte = (pqm1(jl,klev)+zqs(jl)*zhsoil(jl))/2.zmult4 = zfux*zmult5 - 1. zcons = zcons12*paphm1(jl,klevp1)/(ptm1(jl,klev)* & & (1.+vtmpc1*pqm1(jl,klev)-pxm1(jl,klev))) END DO
From Nature
To its
Representation
•LESs can be used in developing/calibrating PBL parameterizations
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
Outlook
•Extend analysis for the full range of boundary layer regimes
•precipitating sc cloud PBLCloud microstructureCloud-aerosol relationships
•turbulence over complex terrain
•PBL with chemically reacting species
•transition from shallow to deep convection
Scientific Advisory Committee Meeting, November 25-26, 2002
Andreas Chlond: Large-Eddy Simulation
The End
Questions