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