Coupling of the Common Land Model (CLM) to RegCM in a Simulation over East Asia Allison Steiner, Bill Chameides, Bob Dickinson Georgia Institute of Technology Atlanta, GA, USA Jeremy Pal, Filippo Giorgi ICTP, 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 RegCM Model simulation over East Asia Comparison to BATS simulation Part II: Application of Coupled Model Aerosol 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) ATMOSPHERE Dynamics, Radiation LAND SURFACE MODEL energy momentum mass (trace gases)

BATS/CLM comparison BATSCLM One canopy layer Simple stomatal conductance model No photosynthesis One snow layer 3 soil layers Soil T: Force-restore Soil moisture: Diffusive/gravitational One canopy layer Sunlit/shaded leaves Stomatal resistance- photosynthesis model TOPMODEL runoff Up to five snow layers 10 uneven soil layers Soil T and moisture: Solved numerically Includes liquid H 2 O/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 CANOPY Leaf Temperature Stomatal resistance Photosynthetic rate ATMOSPHERE Radiation Air temperature Relative humidity Cloud Precipitation SOIL Soil moisture AEROSOL Evapotranspiration Sensible 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 APARShaded APAR

Aerosol-Induced Change in Photosynthesis Sunlit Photosynthetic RateShaded Photosynthetic Rate

Sunlit Leaf Photosynthesis Dependent on Leaf Temperature

Photosynthesis-Stomatal Resistance Relationship Represents the balance between water loss and CO 2 uptake A=photosynthesis r s =stomatal resistance m,b empirical constants c s =surface CO 2 h= vapor pressure deficit term (Collatz et al., 1991)

Changes in the Surface Energy Fluxes Transpiration FluxSensible 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