why climate modelers think we need a really, really big computer phil jones climate, ocean and sea...
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Why Climate Modelers Think We Need a Really, Really Big
Computer
Phil Jones Climate, Ocean and Sea Ice Modeling (COSIM)
Climate Change Prediction ProgramCo-PI SciDAC CCSM Collaboration
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Climate System
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Climate Modeling Goals• Understanding processes and how they
interact (only one on-going experiment)• Attribution of causes of observed climate
change• Prediction
– Natural variability (ENSO, PDO, NAO)– Anthropogenic climate change (alarmist
fearmongering) – IPCC assessments– Rapid climate change
• Input on energy policy
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Climate Change
IPCC TAR 2001
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Greenhouse Gases• Energy production• Bovine flatulence• Presidential campaigning
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Rapid Climate Change
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Polar and THC
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State of the Art
• T85 Atmosphere (150km)• Land on same• 1 degree ocean (100km)• Sea ice on same• Physical models only – no biogeochemistry• 5-20 simulated years per CPU day
– Limited number of scenarios
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Community Climate System Model
OceanPOP
IceCICE/CSIM
AtmosphereCAM
LandLSM/CLM
Flux Coupler
7 States10 Fluxes
6 States6 Fluxes
4 States3 Fluxes
7 States9 Fluxes
6 Fluxes 11 States10 Fluxes
6 States13 Fluxes
6 States6 Fluxes
Once
OnceOnce
Once
perper
perper
day
hour
hour
hour
NSF/DOEPhysical Models(No biogeochem)150km
100km
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Performance
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Performance Portability• Vectorization
– POP easy (forefront of retro fashion)– CAM, CICE, CLM
• Blocked/chunked decomposition– Sized for vector/cache– Load balanced distribution of blocks/chunks– Hybrid MPI/OpenMP– Land elimination
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Performance Limitations
• Atmosphere– Dynamics (spectral or FV), comms– Physics, flops
• Ocean– Baroclinic, 3d explicit, flops/comms– Barotropic, 2d implicit, comms
• All– timestep
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Prediction and AssessmentMany century-scale
simulations (>2500yrs) @~5yrs/day
Cycle vampires:Many dedicated cycles
at computer centers
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Attribution
Stott et al, Science 2000
“Simulations of the response to natural forcings alone … do not explain the warming in the second half of the century”
“..model estimates that take into account both greenhouse gases and sulphate aerosols are consistent with observations over this*period” - IPCC 2001
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The annual mean change of temperature (map) andthe regional seasonal change (upper box: DJF; lower box: JJA) for the scenarios A2 and B2
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The annual mean change of precipitation (map) andthe regional seasonal change (upper box: DJF; lower box: JJA) for the scenarios A2 and B2
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If elected, we plan…
• High resolution– Cloud resolving atmosphere (10km)– Eddy-resolving ocean (<10km)– Regional prediction
• Fully coupled biogeochemistry– Source-based scenarios
• More scenarios, more ensembles– Uncertainty quantification
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Towards Regional Prediction
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Resolution and Precipitation
CCM3 extreme precipitation events depend on model resolution. Here we are using as a measure of extreme precipitation events the 99th percentile daily precipitation amount. Increasing resolution helps the CCM3 reproduce this measure of extreme daily precipitation events.
(DJF) precipitation in the California region in 5 simulations, plus observations. The 5 simulations are: CCM3 at T42 (300 km), CCM3 at T85 (150 km) , CCM3 at T170 (75 km), CCM3 at T239 (50 km), and CAM2 with FV dycore at 0.4 x 0.5 deg.
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Eddy-Resolving Ocean
0.1 deg0.28 deg
Obs 2 deg
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Only decades…
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Chemistry, Biogeochemistry
• Atmospheric chemistry– Aerosols, ozone, GHG
• Ocean biogeochemistry– Phytoplankton, zooplankton, bacteria, elemental cycling,
trace gases, yada, yada…
• Land Model– Carbon, nitrogen cycling, dynamic vegetation
• Source-based scenarios– Specify emissions rather than concentrations
• Sequestration strategies (land and ocean)
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Aerosol Uncertainty
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Atmospheric Chemistry• Gas-phase chemistry with emissions, deposition, transport and photo-
chemical reactions for 89 species. • Experiments performed with 4x5 degree Fvcore – ozone concentration at
800hPa for selected stations (ppmv)• Mechanism development with IMPACT
– A) Small mechanism (TS4), using the ozone field it generates for photolysis rates.
– B) Small mechanism (TS4), using an ozone climatology for photolysis rates.
– C) Full mechanism (TS2), using the ozone field it generates for photolysis rates.
Zonal mean Ozone, Ratio A/C
Zonal mean Ozone, Ratio B/C
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Ocean Biogeochemistry
•Iron Enrichment in the Parallel Ocean Program•Surface chlorophyll distributions in POPfor 1996 La Niña and 1997 El Niño
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Global DMS Flux from the Ocean using POP
The global flux of DMS from the ocean to the atmosphere is shown as an annual mean. The globally integrated flux of DMS from the ocean to the atmosphere is 23.8 Tg S yr-1 .
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Increasing the deficit (1010-1012)
• Resolution (103-105)– x100 horiz, x10 timestep, x5-10 vert
• Completeness (102)– Biogeochem (30-100 tracers)
• Fidelity (102)– Better cloud processes, dynamic land, others
• Increase length/number of runs(103)– Run length (x100)– Number of scenarios/ensembles (x10)
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Storage
• Atmosphere– T85 29 GB/sim-yr, 0.08 GB/tracer– T170 110 GB/sim-yr, 0.3 GB/tracer
• Ocean– 1 1.7 GB/sim-yr, 0.2 GB/tracer– 0.1 120 GB/sim-yr, 17 GB/tracer
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Beyond Moore’s Law
• Algorithms– 50% of past improvements– Tracer-friendly algorithms (inc remap advect)– Subgrid schemes– Implicit or other methods
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Remapping Advection
• monotone• multiple tracers free• 2nd order
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Subgrid Orography Scheme
• Reproduces orographic signature without increasing dynamic resolution
• Realisitic precipitation, snowcover, runoff
• Month of March simulated with CCSM
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Comparison of sea ice shear (%/day) from CICE (a,c) Comparison of sea ice shear (%/day) from CICE (a,c) and ‘old’ (b,d) modelsand ‘old’ (b,d) models
Feb 20, Feb 20, 19871987
Feb 20, Feb 20, 19871987
Feb 26, Feb 26, 19871987
Feb 26, Feb 26, 19871987
(a)(a)
(c)(c)
(b)(b)
(d)(d)
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Beyond Moore’s Law
• New architectures– Improved single-processor performance– Scaling vs. throughput