Coupling of the Common Land Model (CLM) to RegCM in a Simulation over East Asia

Allison Steiner, Bill Chameides, Bob DickinsonGeorgia Institute of Technology

Atlanta, GA, USA

Jeremy Pal, Filippo GiorgiICTP, Trieste, Italy

ICTP Workshop on the Theory and Use of Regional Climate Models

3 June 2003

Outline of Talk

Part I: Coupling of CLM to RegCMModel simulation over East Asia

Comparison to BATS simulation

Part II: Application of Coupled ModelAerosol simulation

Land surface feedbacks

Common Land Model (CLM)

New land surface package for climate models

CLM developed as part of NCAR Community System Model (CCSM)- Community effort model

-Offline model validation (Dai et al., 2003)

-Coupled to the CCM3 (Zeng et al., 2002, Bonan et al., 2002)

BATS currently implemented in RegCM (Dickinson et al., 1993)

ATMOSPHEREDynamics, Radiation

LAND SURFACE

MODEL

energymomentum

mass (trace gases)

BATS/CLM comparison

BATS CLM

One canopy layerSimple stomatalconductance modelNo photosynthesis

One snow layer3 soil layersSoil T: Force-restoreSoil moisture: Diffusive/gravitational

One canopy layerSunlit/shaded leavesStomatal resistance-photosynthesis model

TOPMODEL runoffUp to five snow layers10 uneven soil layersSoil T and moisture: Solved numericallyIncludes liquid H2O/ice

Part I: Simulation Specifics

Domain: East Asia 60km resolution Two month spinup One year simulation

(Aug 94 - Aug 95) Two runs: one

BATS, one CLM Similar land cover

characteristics Kuo, SUBEX precip

schemes

Precipitation

East Asian Monsoon: dry winters, wet summers

Winter, Spring: Both models overpredict

CLM slightly less precip annually and in summer

Use of CLM does not strongly affect precipitation

Temperature

Surface temperatures underestimated for both simulations

CLM tends to improve winter cold bias by ~1 degree

CLM slightly amplifies diurnal cycle

Surface Energy Balance

CLM absorbs more radiation due to lower albedos

CLM simulates more sensible heat flux and less latent heat flux

Surface Water Balance

CLM has less precipitation

CLM simulates more runoff than BATS

CLM simulates less evapotranspiration

Annually, less water entering the soil in CLM

Evapotranspiration

CLM has less ground evaporation

BATS/CLM canopy evaporation similar

CLM has more transpiration

Soil Moisture

CLM increases surface soil water (first 10cm)

But decreases root zone soil water (first ~1-2 m)

Related to changes in evapotranspiration components

Snow and Albedo Feedbacks

CLM has less snow at surface

CLM has warmer air temperatures, indicating less snowfall

Snow parameterizations are quite different (e.g., melt and layer structure)

Snow and albedo feedbacks are likely contributing to temperature differences

Summary of Part I

CLM simulates seasonal cycle in East Asia CLM slightly improves winter cold bias Surface hydrology simulated differently

between BATS and CLM CLM simulates much less snow than BATS

over East Asia

Part II: Aerosol-Surface Feedbacks

CANOPYLeaf TemperatureStomatal resistancePhotosynthetic rate

ATMOSPHERERadiationAir temperatureRelative humidityCloudPrecipitation

SOILSoil moisture

AEROSOL

EvapotranspirationSensible heat flux

SURFACE FLUXES

Inclusion of Aerosols

For East Asia, simulated offline aerosol fields– Sulfate– Black Carbon– Organic Carbon– Ammonium– Nitrate

5 Day Simulation 2-6 July 1995 Direct Effect Two runs

Control run (bkg aerosols) and aerosol run Optical depth for aerosol simulation

Change in Absorbed Photosynthetically Active Radiation (APAR) (no aerosol-aerosol)

Sunlit APAR Shaded APAR

Aerosol-Induced Change in Photosynthesis

Sunlit Photosynthetic Rate Shaded Photosynthetic Rate

Sunlit Leaf Photosynthesis Dependent on Leaf Temperature

0

2

4

6

8

10

12

14

-5 5 15 25 35 45

Leaf Temperature (oC)

A (m m

ol C

O2

m-2

s-1

)

Photosynthesis-Stomatal Resistance Relationship

Represents the balance between water loss and CO2 uptake

A = photosynthesis

rs = stomatal resistancem,b empirical constants

cs = surface CO2 h = vapor pressure

deficit term

bphc

Am

r sss

1

bhc

Am

r ss

1

(Collatz et al., 1991)

Changes in the Surface Energy Fluxes

Transpiration Flux Sensible Heat Flux

Summary of Part II

Under certain conditions, aerosols can increase photosynthesis in sunlit leaves

Can alter surface energy balance– Increase transpiration– Reduce sensible heat

Implications for atmospheric boundary layer– Temperature– Relative humidity– Cloud cover– Precipitation

Future Work

Include in new RegCM version? Validate snow over East Asia Investigate tile capability of CLM More investigation on aerosol-land surface

feedbacks

Acknowledgements

NASA Earth System Science Fellowship Filippo Giorgi, Jeremy Pal and PWC group