model systems at mpi-m - max planck society · climate models and earth system models example 1...
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What is a model in climate research as used here for IPCC?
What is a model?Components of the climate systemClimate models – What is inside?Climate models – Resources
Models available at the MPI-MModels used for IPCC simulations
Summary
What is a model?
A model is:an idealized representation or abstraction of an object with the purpose to demonstrate the most relevant or selected aspects of the object or to make the object accessible to studies
Purpose of modelsTo reduce the complexityTo avoid details that are not relevant for a specific considerationTo obtain a theoretically or practically manageable system
What is a model?Example 1: Architecture
http://www.werk-plan.de/
Representation of a building at the scales of a shoe boxWood+acryl instead of concrete, glas, etc.Overview of the object and its relation to the environmentNo details
What is a model?Example 2: Fashion
http://www.stern.de/lifestyle/mode/
The ideal lady to present a dress in the spirit of the designerTrue scaleFlawless/perfect
What is a model?Example 3: Climate model
Climate model are a mathematical abstraction of the observed real worldClimate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice = the Earth system.They follow theoretical principles and observed relationshipsModel = simplified image representing the relevant features http://www.solarviews.com/cap/earth/
Components of the climate systemAtmosphere
DynamicsPhysicsChemistryAerosols
Ocean
DynamicsPhysicsBiogeochem.
Land
HydrologyVegetation
Society Economics Land use
Climate models and Earth system modelsExample 1
0-dimensional model of the radiative equilibrium of the Earth
(1 - a)S πr2 = 4πr2 σT4 π = 3.14159 Piσ = 5.67⋅10-8 JK-4m-2s-1 Stefan-Boltzmann constant S = 1367 Wm-2 incoming solar radiationa = 0.37 to 0.39 fraction reflected back to spacer = 6371 km Earth radius
emitted thermal
radiation
absorbed solar
radiation
→ T= ~ –26ºC = effective emission temperature of Earth→ 35ºC colder than the observed average surface temperature
Problem: Greenhouse gas effect is neglected
Climate models and Earth system models Example 2
3-dimensional comprehensive general circulation models or Earth System Models
GCM's discretize the equations for fluid motion and integrate these forward in time.
They also contain parametrisations for processes - such as convection - that occur on scales too small to be resolved directly.
Earth system models represent the pinnacle of complexity in climate models and internalise as many processes as possible, including chemistry in the atmosphere, marine biogeochemistry, land vegetation etc.
Limits: computer power
Climate models and Earth system models 1. System of continuous equations
Equations describing the evolution of a set of variablesdescribing the state of the modeled systemScale analysis include the “relevant” processes, neglect others
Equation for temperature in the atmosphere,as used for the Hamburg atmospheric GCM (ECHAM5):
Cannot be solved directly on a computer
Climate models and Earth system models 2. System of discretized equations
Equation must be discretized in time and spaceto be accessible to computational solutionsDiscretized equations
time time stepsHamburg atmosphere model for IPCC: 15 minutesHamburg ocean model for IPCC: 1 day
Space horizontal grids or spectra, vertical gridsProblems of too low resolution:
Inaccurate numerical solution of equationsMissing details in the description of the surface: Mountain ranges
Resolution matters1. Spatial resolution in ECHAM5 and errors
Dimensionless error in ECHAM5Horizontal res.: T21 to T159 Vertical res.: L19 to L31 Reference: ERA-15 re-analysis.
Error of T21L19 = 100Error of T63L31 = 50
Error of ERA-40 = 20
IPCC, carbonT63L31
Aerosol T63L19
T21: 5.6°×5.6°T63: 1.9°×1.9°T159: 0.75°×0.75 °
L19: 19 levels, 30km L31: 31 levels, 30km
RMS error of seasonal average patterns of T, Z, U at 200, 500, 850 hPa and SLP compared to Era-15
Resolution matters2. Precipitation REMO 1/2 ° (1979REMO 1/2 ° (1979--93)93)
Annual precipitation in the Alps in observations and in the REMO regional model
ObservationsObservations (1971(1971--90)90) REMO 1/6 ° (1979REMO 1/6 ° (1979--88)88)
source: ETH, source: ETH, ZürichZürich
General circulation models3. Parameterizations
Processes on unresolved scales have effects on resolved scalesThese effects must be described as functions of the resolved fields
ParameterizationsUnresolved dynamics
TurbulenceConvectionGravity waves in the atmosphere
Processes at microphysical or molecular levelRadiationClouds and precipitation in the atmospherePhotosynthesis in plants or plankton…
General circulation models4. Translation to a computer program
Climate models have grown over time with the increasing knowledge on details of processes and the improved power of computers High performance computing requires additional complex structures in the codes
Example: MPI-M climate model for IPCCca. 140000 lines of code = 1700 printed pages
Errors / Bugs : unavoidableLarge bugs are easily detectableMinor bugs are not obvious, hence not easily found
General circulation models5. Verification of Climate models
Careful testing is necessaryTo justify the choice of equationsTo understand effects of the discretization and selected resolutionTo decide if the model is fit for specific applications, e.g. IPCC
Validation of models in standard tests for which acceptable references are known from observations or proxy data
Tests of individual components: atmosphere, ocean, landTests of the coupled system, which may drift to unrealistic statesExample of a coupled phenomenon: El Nino/La Nina
Validation is based on the observed climate of the pastCredibility of simulations for the future (IPCC) is based on the “success” of modeling the climate of the past
General circulation models6. Climate simulations and resources
Resources consumed by IPCC simulations:Simulated years for all IPCC related experiments computed at the DKRZ: 3500 yearsConsumed computer time: 400000 CPU hours =
550 CPU months =~12 months on ¼ DKRZ SX-6
Generated raw data: 400 TBData in IPCC data bank: 80 TB
(c.f. hard disk in a PC: 200 GB)
Substantial effort in work and money
Models available at the MPI-M
Atmosphere GCM
Dynamics global: ECHAM5, regional: REMO+PhysicsAerosols HAM(M7)
Ocean+Ice GCM
Dynamics MPI-OM+PhysicsBiogeochem. HAMOCC/DMS
Land model
Hydrology HDVegetation JSBACH
The IPCC model
MomentumEnergy
H2O
Sun/Spaceconst. Irrad.
Energy AtmosphereECHAM5 T63 L31
OceanMPIOM 1.5°L40
LandECHAM5/HD
IPCCA1B, B1, A2
GHG conc.SO4 conc.
PRISM
The aerosol model
MomentumEnergy
H2O
Sun/Space11y cycle
Energy
AtmosphereECHAM5 T63 L19
HAM
OceanMPIOM 1.5°L40HAMOCC+DMS
LandECHAM5/HD
IPCC,NIESA1B
GHG conc.SO2 em.BC em.OC em.
PRISM
DMS
dust
Volcanoes
The carbon cycle model
MomentumEnergy
H2O
Sun/Space
Energy
AtmosphereECHAM5 T63 L31
OceanMPIOM 1.5°L40
HAMOCC
LandHD, JSACH
IPCCA1B
CO2 em.CH4, N2O conc.
SO4 conc.
PRISM
Global MPI-M model systems for IPCC
IPCC model Most presentations
Aerosol model Johann Feichter
Carbon cycle model Christian Reick
Daniela JacobRegional model
ConclusionsClimate models are the only tool to explore the climate systematically
Models as used for IPCC are comprehensive but still simplifications of the real world
Their success in the simulation of the climate of the well observed past is the basis for simulations into the future.
3 global models + 1 regional model have been used at the MPI-M:Physical system IPCC computations IPCC data baseAerosol systemCarbon cycle system