Introduction to Atmospheric Climate Modeling

(CAM within CCSM)Phil Rasch

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

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)

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)

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

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

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)

Examples of Global Model Examples of Global Model ResolutionResolution

Typical Climate Application Next Generation Climate Applications

Vertical resolutionVertical resolution

Resolution near sfc 100m

Resolution near tropopause is > 1000m

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

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

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

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

Initial ConditionsInitial ConditionsPassive Tracer TestsPassive Tracer Tests

Mixing ratio = 1 (single layer)

= 0

(elsewhere)

Mixing in Mid-latitude

UTLS

Descent in sub-tropics, subtropical barrier

Mixing into Free Troosphere and PBL

Simple Ozone StudiesSimple Ozone Studies

• Source in Stratosphere– Fixed concentration (Pseudo-Ozone)– Fixed emissions (SYNOZ)

• Sink near surface

Pseudo-Ozone test case

SYNOZ test caseSYNOZ test case

Spectral solution FV solution

Ratio of POZONE/SYNOZRatio of POZONE/SYNOZSpectral solution FV solution

More rapid exchange

Coupled Models allow biases to Coupled Models allow biases to growgrow

CAM CCSM

Revised/Dilute

Standard/Undilute

JJA FV 2x2.5 1979-1988

Modifications to CAM Convection by Neale & Mapes

Observationally based

Dilute

Undilute

Sea Ice Sea Ice Distribution in Distribution in

coupled coupled simulation after simulation after

200yrs200yrs

Finite Volume

Spectral

Low Viscosity Control

Low Viscosity minus Control Control minus HadiSST

The end

Nino 3 evaluation fromNino 3 evaluation fromyears 20-40 of FV runyears 20-40 of FV run

Dilute parcel modification

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

• 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

• 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.

• 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

• 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