Model Systems at MPI-M. Marco Giorgetta

Transcription

1 Model Systems at MPI-M Marco Giorgetta

2 Content What is a model in climate research as used here for IPCC? What is a model? Components of the climate system Climate models What is inside? Climate models Resources Models available at the MPI-M Models used for IPCC simulations Summary

3 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 models To reduce the complexity To avoid details that are not relevant for a specific consideration To obtain a theoretically or practically manageable system

4 What is a model? Example 1: Architecture Representation of a building at the scales of a shoe box Wood+acryl instead of concrete, glas, etc. Overview of the object and its relation to the environment No details

5 What is a model? Example 2: Fashion The ideal lady to present a dress in the spirit of the designer True scale Flawless/perfect

6 What is a model? Example 3: Climate model Climate model are a mathematical abstraction of the observed real world Climate 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 relationships Model = simplified image representing the relevant features

7 Components of the climate system Atmosphere Dynamics Physics Chemistry Aerosols Society Economics Land use Ocean Dynamics Physics Biogeochem. Land Hydrology Vegetation

8 Climate models and Earth system models Example 1 0-dimensional model of the radiative equilibrium of the Earth (1 - a)s πr 2 = 4πr 2 σt 4 π = Pi absorbed solar radiation emitted thermal radiation σ = JK -4 m-2s -1 Stefan-Boltzmann constant S = 1367 Wm -2 incoming solar radiation a = 0.37 to 0.39 fraction reflected back to space r = 6371 km Earth radius T= ~ 26ºC = effective emission temperature of Earth 35ºC colder than the observed average surface temperature Problem: Greenhouse gas effect is neglected

9 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

10 Climate models and Earth system models 1. System of continuous equations Equations describing the evolution of a set of variables describing the state of the modeled system Scale 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

11 Climate models and Earth system models 2. System of discretized equations Equation must be discretized in time and space to be accessible to computational solutions Discretized equations time time steps Hamburg atmosphere model for IPCC: 15 minutes Hamburg ocean model for IPCC: 1 day Space horizontal grids or spectra, vertical grids Problems of too low resolution: Inaccurate numerical solution of equations Missing details in the description of the surface: Mountain ranges

12 Horizontal grid of the MPI ocean model [Every 5 th grid line shown] North pole South pole

13 Resolution matters 1. Spatial resolution in ECHAM5 and errors Dimensionless error in ECHAM5 Horizontal res.: T21 to T159 Vertical res.: L19 to L31 Reference: ERA-15 re-analysis. Error of T21L19 = 100 Error of T63L31 = 50 Error of ERA-40 = 20 Aerosol T63L19 IPCC, carbon T63L31 T21: T63: T159: 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

14 Resolution matters 2. Precipitation REMO 1/2 ( ) 93) Annual precipitation in the Alps in observations and in the REMO regional model Observations ( ) 90) REMO 1/6 ( ) source: ETH, Zürich

15 General circulation models 3. Parameterizations Processes on unresolved scales have effects on resolved scales These effects must be described as functions of the resolved fields Parameterizations Unresolved dynamics Turbulence Convection Gravity waves in the atmosphere Processes at microphysical or molecular level Radiation Clouds and precipitation in the atmosphere Photosynthesis in plants or plankton

16 General circulation models 4. 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 IPCC ca lines of code = 1700 printed pages Errors / Bugs : unavoidable Large bugs are easily detectable Minor bugs are not obvious, hence not easily found

17 General circulation models 5. Verification of Climate models Careful testing is necessary To justify the choice of equations To understand effects of the discretization and selected resolution To 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, land Tests of the coupled system, which may drift to unrealistic states Example of a coupled phenomenon: El Nino/La Nina Validation is based on the observed climate of the past Credibility of simulations for the future (IPCC) is based on the success of modeling the climate of the past

18 General circulation models 6. Climate simulations and resources Resources consumed by IPCC simulations: Simulated years for all IPCC related experiments computed at the DKRZ: 3500 years Consumed computer time: CPU hours = 550 CPU months = ~12 months on ¼ DKRZ SX-6 Generated raw data: Data in IPCC data bank: 400 TB Substantial effort in work and money 80 TB (c.f. hard disk in a PC: 200 GB)

19 Models available at the MPI-M Atmosphere GCM Dynamics +Physics Aerosols global: ECHAM5, regional: REMO HAM(M7) Ocean+Ice GCM Dynamics +Physics Biogeochem. MPI-OM HAMOCC/DMS Land model Hydrology Vegetation HD JSBACH

20 The IPCC model Sun/Space const. Irrad. IPCC A1B, B1, A2 Energy Momentum Energy H2O PRISM Atmosphere ECHAM5 T63 L31 Land ECHAM5/HD Ocean MPIOM 1.5 L40 GHG conc. SO4 conc.

21 The aerosol model Sun/Space 11y cycle Energy Momentum Energy H2O Atmosphere ECHAM5 T63 L19 HAM Land ECHAM5/HD IPCC,NIES A1B GHG conc. SO 2 em. BC em. OC em. Volcanoes PRISM Ocean MPIOM 1.5 L40 HAMOCC+DMS dust DMS

22 The carbon cycle model Sun/Space Energy Momentum Energy H2O PRISM Atmosphere ECHAM5 T63 L31 Land HD, JSACH Ocean MPIOM 1.5 L40 HAMOCC IPCC A1B CO 2 em. CH 4, N 2 O conc. SO 4 conc.

23 The regional model for IPCC Sun Global data from IPCC model simulations Atmosphere+Land REMO

24 Global MPI-M model systems for IPCC IPCC model Most presentations Aerosol model Johann Feichter Carbon cycle model Christian Reick Regional model Daniela Jacob

25 Conclusions Climate 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 base Aerosol system Carbon cycle system

26 The End