Preliminary Results of Global Preliminary Results of Global Climate Simulations With a High-Climate Simulations With a High-Resolution Atmospheric ModelResolution Atmospheric Model

P. B. Duffy, B. Govindasamy, J. Milovich, P. B. Duffy, B. Govindasamy, J. Milovich, K. Taylor, S. Thompson, M. WehnerK. Taylor, S. Thompson, M. Wehner

Lawrence Livermore National LaboratoryLawrence Livermore National Laboratory

With help fromWith help fromJ. J. Hack, NCARJ. J. Hack, NCAR

Pushing the limits of climate model resolution:• Why do it?• What have we done?• What have we learned?

ContentsContents

Why Try to Increase Model Resolution?Why Try to Increase Model Resolution?

To allow global climate models to give meaningful results on regional scales.

• This will allow assessments of societal impacts of climate change

To improve simulations of terrestrial Carbon cycle• Results sensitive to precip. and surface temperature

Higher resolution• Includes fine-scale detail• Improves results on large scales

What Are Our Goals?What Are Our Goals?

Assess computational issues associated with running the model at high resolution;

Evaluate the realism of the simulated climate at high resolution vs. coarse resolution;

Examine resolution dependence of atmospheric response to increased greenhouse gases.

Pushing the limits of climate model resolution:• Why do it?• What have we done?• What have we learned?

ContentsContents

Six High-Resolution Simulations are Six High-Resolution Simulations are Complete or in ProgressComplete or in Progress All simulations use the CCM3 atmospheric model forced by prescribed

sea-surface temperatures (SSTs) Analagous T42 simulations also have been performed

1. A present-climate simulation at T170 (512 x 256 cells)• Forced with climatological observed sea-surface temperatures• 12 simulated years completed

2. An increased GHG simulation at T170• Forced with predicted SSTs for 2100 based on SST CHANGES

from a coarse-resolution coupled model (CSM) simulation• 12 simulated years completed

Both of above use “untuned” (i.e. tuned for T42) model

• 3. A present climate simulation at T170 with “tuned” model• 6 simulated years completed

Simulations Complete or in Progress…Simulations Complete or in Progress…

• 4. An AMIP simulation at T239 (720 x 360 cells)• Forced with observed sea-surface temperatures for 1979-

1987• 6 years completed with untuned model

5. A present-climate simulation at T239• Uses model tuned for T170• ~1 simulated year completed so far

n 6. A present-climate simulation at T340 (!) (1024x512 grid cells)• This is short (1 simulated month)

Observations on Some Observations on Some Computational IssuesComputational Issues

We Have Run the High Resolution Model We Have Run the High Resolution Model on A Variety of Machineson A Variety of Machines

Lab Machine Vendor Model # nodes

CPUs/node

CPU type

Notes

LLNL White IBM RS/6000 SP

512 16 (NH-2)

Power 3 375 Mhz

World’s # 1

LLNL Frost IBM RS/6000 SP

68 16 (NH-2)

Power 3 375 Mhz

NERSC gseaborg IBM 4

NERSC seaborg IBM RS/6000 SP

208 16 Power 3 375 Mhz

World’s # 2

LLNL TC2000 Compaq 118 4 EV67 667 Mhz

LLNL PCR ??? 128? 2 Pentium4

Linux cluster

Computational Issues…Computational Issues…

• speedup curve on NERSC gseaborg machine

A Preliminary Look at Selected Results:A Preliminary Look at Selected Results:

Simulations of Present ClimateSimulations of Present Climate

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S=1N

fn −f( )− rn −r( )[ ]2

n=1

N∑⎧ ⎨ ⎩ ⎫ ⎬ ⎭

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σrσ f

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θ =1N

fn− f( ) rn−r( )n=1

N∑σfσr

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σf =fn− f( )

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R=σf

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Example“Taylor Diagram”

Result of ideal model would be plotted here

Two Points About Our Taylor DiagramsTwo Points About Our Taylor Diagrams

1. Taylor diagrams do not show errors in means (I.e. biases)

2. Comparison was performed on T42 grid

Thus, we are assessing how finer resolution affects large-scale results

Variables and primary validation data setsVariables and primary validation data sets Variable Abbrv. Observation Comment

Surface air temperatureOutgoing longwaveClear-sky outgoing LWOutgoing shortwaveClear-sky outgoing SWCloud fraction

Geopotential heightPrecipitable waterSea level pressureAir temperatureWindsPrecipitation

Sensible heat fluxLatent heat fluxZonal wind stressMeridional wind stress

TASOLRLWCSSWSWCSCLT

ZPRWPSLTU, VP

SHLHTAUUTAUV

Jones/PCMDIERBEERBEERBEERBEISCCP

ECMWFECMWFECMWFECMWFECMWFXie & Arkin

(NCEP)COADSCOADSCOADSCOADS

merger of available data

Nearly global coverage bysatellites (1985 -1988)

best coverage available(1984-1988)

reanalysis

merged land and satellitedata

empirically calculated,based on available data

Effects of Increasing Resolution From T42 -> T170

Model Improvement: AMIP 1 vs. AMIP 2Model Improvement: AMIP 1 vs. AMIP 2

CLT cloud fraction

P precipitation

PSL sea level pressure

PRW precipitable water

SH sensible heat

T200 200 hPa temperature

τu zonal wind stress

τv meridional wind stress

U200 200 hPa zonal wind

V200 200 hPa meridional wind

Z500 500 hPa geopotential height

T42 -> T170 AMIP 1 -> AMIP 2

Increasing Resolution vs. Actual Thinking

Effects of Increasing Resolution From T170->T239

old

Effects of Tuning on Spatial Patterns of Results at T170

old

Tuning Reduces BiasesTuning Reduces Biases

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color= Etuned−Euntuned

(Etuned+Euntuned) /2where

E = f −r( )2

Precipitation Over USAPrecipitation Over USA

DJF Precipitation over USA gets Better as DJF Precipitation over USA gets Better as Resolution IncreasesResolution Increases

JJA Precipitation Over USAJJA Precipitation Over USA

As Resolution Increases, Convective As Resolution Increases, Convective Precipitation Decreases…Precipitation Decreases…

… … and Large-Scale Precipitation Increasesand Large-Scale Precipitation Increases

Arctic Climate and Sea IceArctic Climate and Sea Ice

Many Climate Models Simulate Arctic Many Climate Models Simulate Arctic SLP Distribution Poorly…SLP Distribution Poorly…

JJA sea level pressure distribution is more realistic at T170 than at T42

Effects of Increased Effects of Increased Greenhouse GasesGreenhouse Gases

We Calculate SST change from Coarse-We Calculate SST change from Coarse-Resolution Coupled Model (CSM) SimulationResolution Coupled Model (CSM) Simulation

Simulated Time

Sea

Sur

face

Tem

pera

ture

1990s 2090s

Regional Details of Predicted Climate Regional Details of Predicted Climate Changes Can be Very Different at T170Changes Can be Very Different at T170

T42

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are needed to see this picture.

T170

QuickTime™ and aCinepak decompressor

are needed to see this picture.

T239

QuickTime™ and aCinepak decompressor

are needed to see this picture.

What Have We Learned?What Have We Learned? It is possible to run short global climate simulations at 50 - 75 km

resolution. CCM3 is reliable but not efficient at these resolutions;

• Eulerian spectral dynamics seems to run inefficiently at high resolution.

Physics parameterizations seem robust to an increase in resolution• Most likely, retuning, but not reformulation, is needed.

In most aspects, large-scale results are more realistic at T170 than at T42; T239 is even better. I.e. using high resolution improves the large-scale results.

Partial re-tuning of cloud and hydrological parameters removes biases but has little effect on spatial patterns.

Climate changes due to increased greenhouse gases at T170 vs. T42 are very similar globally, but quite different regionally.

What’s Next? With More Funding, We CouldWhat’s Next? With More Funding, We Could Work with the NCAR Environmental and Societal Impacts Group

(ESIG) to design simulations of maximum benefit to the impacts community

• Use appropriate CO2 scenarios• Save needed climate statistics• Distribute output to the community;

“Downscale” to fine resolution results of climate forecasts to be performed by NOAA;

Drive a 20 km nested model with output from our global T170 model;

Perform Initial Tendency Error Analysis (ITEA) at high resolution;

Compare results of high-resolution global model to those of a nested model at same resolution;

What’s Next?…What’s Next?… Run the new NCAR model (CAM1) at high resolution

• Investigate computational behavior (scaling, etc.)• Evaluate simulated climate;

Perform a short coupled-model simulation with the atmosphere at high resolution;

Can high-resolution atmosphere improve simulation of Arctic sea ice?

• Force sea ice model with winds, etc. from high-resolution atmospheric model;

Does higher resolution improve simulation of terrestrial C-cycle?

Go to even higher resolution

Etc.

We will make model output available for analysisWe will make model output available for analysis

If interested, contact me:

pduffy@llnl.gov