introduction to atmospheric climate modeling (cam within ccsm) phil rasch
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Introduction to Atmospheric Climate Modeling
(CAM within CCSM)Phil Rasch
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What is CCSM?What is CCSM?
Coupler(CPL6)
Atmosphere(CAM3)
Ocean(POP)
Sea Ice(CSIM5)
Land(CLM3)
Aerosols
Trop ChemAerosols
Strat ChemWACCM
Isotopes
(H,C,O)
Isotopes
(H,C,O) DynamicVegetation
Isotopes
(H,C,O)
BioGeochemistry
BioGeochemistry
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Some comments on CCSM Some comments on CCSM configurationsconfigurations
• All components can be interactive
• All components can be replaced with “data models”– Information about that component is
prescribed --- read in from an external dataset
• CAM can be run with – Full interaction– As a Chemical Transport Model
(acts as a processor and conduit for exchangebetween other model components)
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Implementation Details in the Implementation Details in the atmosphere of possibleatmosphere of possible
interest to the classinterest to the class• Model performs sequential applications of a
number of physical processes– State variables (temperature, winds, density, water
substances, trace constituents) are updated after each process representation is applied
• We typically divide processes into two classes– “Dynamics” (the equations of motion = Navier Stokes
equations simplified to assume hydrostatic balance in the vertical)
• Dynamics = dynamical core = instantaneous solution requires information in latitude, longitude, and height!
– “Physics” (diabatic processes such as radiative transfer, processes involving water phase change, chemistry, etc)
• Physics = parameterizations = solutions generally only require information in height = work on a column by column basis
– “Transport” (sometimes)
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Time LoopTime LoopDynamics
Shallow Convection
Moist DeepConvection
Dry Adiabatic LapseRate Adjustment
Boundary LayerProcesses
Coupling to land/ocean/ice
Chemistry
Radiation
Stratiform Clouds,Wet Chemistry,
Aerosols
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CAM dynamical configurations CAM dynamical configurations available for useavailable for use
• Spectral dynamics, semi-Lagrangian transport (SLT) for tracers --- Traditional– Spherical harmonic discretization in horizontal– Low order finite differences in vertical– Inconsistent, Non-conservative -> fixers required for
tracers
• Semi-Lagrangian Dynamics, semi-Lagrangian Transport for tracers– Polynomial representation of evolution of “mixing
ratios” for all fields– Inconsistent, Non-conservative -> fixers required for
tracers
• Finite Volume (FV) using “flux form semi-Lagrangian” framework of Lin and Rood– Semi-consistent, fully conservative
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Standard ResolutionsStandard Resolutions
• Spectral and Semi-Lagrangian dynamics – (~2.8x2.8 degree)– 26 layers from surface to 35km– (optional ~4x4 resolution (T31!) through ~0.5x0.5)
• Finite Volume – (2x2.5 degree) – 26 layers from surface to 35km– (optional 4x5 resolution through 1x1.25)– (optional WACCM surface to 150km)– Half Atmosphere version (to 70km)
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Examples of Global Model Examples of Global Model ResolutionResolution
Typical Climate Application Next Generation Climate Applications
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Vertical resolutionVertical resolution
Resolution near sfc 100m
Resolution near tropopause is > 1000m
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High-Resolution Global ModelingHigh-Resolution Global Modeling
Courtesy, NASA Goddard Space Flight Center Scientific Visualization Studio
Reference Panel
Still a Need to Treat Subgrid-Scale Processes
zoom T42 Grid
Galapagos Islands
Panama
~ 130 km
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What can you do with these What can you do with these models/tools?models/tools?
• Use them as our most comprehensive statement of the earth’s climate system to explore the behavior of the system, E.g.:– IPCC Assessments– Interpreting & understanding the climate
record
• Attempt to improve the representation of component processes within this tool– Leads to a better understanding of the
component processes– Leads to a better understanding of the
interactions between processes
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Some examples of Exploration of Some examples of Exploration of component processes and their component processes and their
interactionsinteractions
• Sensitivity of transport processes to numerical representations
• How our formulation of convection influences the climate system
• How component models, numerics and physics interact to influence our ability to represent the climate system
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Tracer ExperimentsTracer Experiments
– http://www.csm.ucar.edu/publications/jclim04/Papers_JCL04.html
– Co-authors: D. B. Coleman, N. Mahowald, D. L. Williamson, S. J. Lin,
B. A. Boville and P. Hess
• Passive Tracers (short 30 day runs)
• Radon
• SF6/Age of Air
• Ozone
• Biosphere Carbon Source
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Initial ConditionsInitial ConditionsPassive Tracer TestsPassive Tracer Tests
Mixing ratio = 1 (single layer)
= 0
(elsewhere)
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Mixing in Mid-latitude
UTLS
Descent in sub-tropics, subtropical barrier
Mixing into Free Troosphere and PBL
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Simple Ozone StudiesSimple Ozone Studies
• Source in Stratosphere– Fixed concentration (Pseudo-Ozone)– Fixed emissions (SYNOZ)
• Sink near surface
Pseudo-Ozone test case
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SYNOZ test caseSYNOZ test case
Spectral solution FV solution
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Ratio of POZONE/SYNOZRatio of POZONE/SYNOZSpectral solution FV solution
More rapid exchange
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Coupled Models allow biases to Coupled Models allow biases to growgrow
CAM CCSM
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Revised/Dilute
Standard/Undilute
JJA FV 2x2.5 1979-1988
Modifications to CAM Convection by Neale & Mapes
Observationally based
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Dilute
Undilute
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Sea Ice Sea Ice Distribution in Distribution in
coupled coupled simulation after simulation after
200yrs200yrs
Finite Volume
Spectral
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Low Viscosity Control
Low Viscosity minus Control Control minus HadiSST
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The end
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Nino 3 evaluation fromNino 3 evaluation fromyears 20-40 of FV runyears 20-40 of FV run
Dilute parcel modification
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Current formulations and Current formulations and changes on the horizonchanges on the horizon
• Boundary Layer formulation
• No knowledge of moist physics
• No knowledge of entrainment due to cloud/radiation interaction
• New Shallow and PBL from Bretherton and Colleagues
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• Cloud Fraction– Current formulation uses RH and stability
following Sundqvist, J. Slingo, Klein/Hartmann– New formulation uses a PDF based approach
followingTompkins, Johnson• Ties fraction, condensate, and physical processes together
much more tightly
• Cloud Condensate– Bulk formulation, mass only, (number prescribed or
function of aerosols mass (Boucher and Lohmann)• (liquid and ice drops, snow and rain)• Condensate advected and sediments
– Next generation will predict mass and number, better representation of exchange between liquid and ice
– New formulation will have more realistic characterization of ice crystal size, shape, partitioning of mass/number relationships
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• Scavenging– Current formulation tied directly to production of
condensate, production and evaporation of rain in stratiform clouds
– Formulation for convection a bit hokey. Have separated transport processes from microphysics in attempt to avoid too tight coupling of scavenging to a particular convective parameterization
– Time scale for mixing between cloud and environment = model physics timestep (30-60 minutes)
• New Scavenging formulation????– Increase connection and consistency between other
processes.
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• Convection– A variety of schemes are under
consideration• Modified closure for Zhang/McFarlane scheme• Donner (vertical velocity spectra, meso-scale
circulations)• Emanuel (bouyancy sorting formulation)• Kain Fritsch?• Super-parameterizations
– Neural net
• 3 or 4 other possibilities
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• Aerosols– Current formulations are all bulk forms for mass only
• Externally mixed• BC, OC, Sulfate are assumed submicron• Sea Salt Dust have 4 bins, with range up to about 10
microns• Hydrophobic Hydrophilic on 1.5 day timescale• Quite old inventories (except sulfate)
– Next generation• Better inventories• Tied to CLM much more closely (fire, VOC, N, C)• Aerosol number? Internal mixtures?• Tied to cloud microphysics more closely