John J. Cassano, Matthew Higgins, Alice DuVivierUniversity of Colorado

Wieslaw Maslowski, William Gutowski, Dennis Lettenmaier, Andrew Roberts

Project goalsDevelop a state-of-the-science regional

Arctic system model (RASM)

Why do we want a high resolution atmospheric model in RASM?The atmosphere forces and is forced by all other

components of the climate systemSmall-scale features in the atmosphere can have

large impacts on climatically important processes such as:Cyclone intensity / polar lowsMesoscale features such as topographically forced winds

(Greenland tip jets)

Realistic representation of these processes is critical for improved climate projection

Cyclone Intensity and SizeResolution impacts the size and intensity of cyclones

AMPS simulates lower pressure and smaller cyclones than all reanalyses

Stronger and smaller storms will impact air-sea coupling as well as impact humanactivities in polar regions

Mesoscale Features: Greenland tip jets

Topographically forced mesoscale winds can be very strong but are poorly resolved in low resolution models

These winds drive large sensible and latent heat fluxes

10 m

wind speed (2/21/07)

a) b) c)

d) e)

a) b)

c) d)

Two Month: WRF average latent heat flux

a) b)

c) d)

Two Month: WRF 95th percentile latent heat flux

RACM simulationsCoupled: Regional Arctic Climate Model (RACM)

WRF – POP – CICE - VICSimulation from 1989 to 2002 (currently)

Atmosphere – land : WRF – NoahCORDEX simulation from 1989 to 2009

RACM and WRF simulations forced with:ERA-Interim IBC/LBCsObserved sea iceUse spectral nudging of wave numbers 1 and 2

Comparison presented here will focus on 1990 to 2002

Coupling Problems: Precipitation (Jan and July 1990)

Coupling Problems: Tsfc Impacts (July 1990)

Coupling Problems: SLP Impacts (July 1990)

ERA-Interim WRF

1989-2002 DJF Climatology

RACM

RACM – ERA-InterimERA-Interim & RACM WRF – ERA-Interim

ERA-Interim WRF

1989-2002 JJA Climatology

RACM

RACM – ERA-InterimERA-Interim & RACM WRF – ERA-Interim

ERA-Interim

1989-2002 JJA Climatology

RACM

RACM – ERA-InterimERA-Interim & RACM

RACM - NSIDC

1989-2002 JJA and DJF Climatology

RACM – ERA-Interim DJF WRF – ERA-Interim DJF

RACM – ERA-Interim JJA WRF – ERA-Interim JJA

1989-2002 DJF Climatology

Temperature

Part of Russia

Temperature

North of 80 Latitude

Northern Alaska

Temperature

RACM – ERA-Interim DJF

WRFRACM

WRFRACMWRF

RACM

1989-2002 DJF Climatology

WRF – ERA-Interim DJF RACM – WRF DJF

RACM – WRF DJFWRF – ERA-Interim DJF

Precipitation Difference (%)

Snow Water Equivalent Difference (kg m-2)

RACM – ERA-Interim DJF

RACM – ERA-Interim DJF

ConclusionsUse RASM to explore the impact of small-scale

atmospheric processes on the coupled climate systemGreenland tip jet showed large change in surface heat

fluxes with increased resolutionCare must be taken when coupling model

componentsPrecipitation problem in early versions of RACM

Current version of RACM is stableErrors in coupled simulations are similar to those in

atmosphere-only simulations, with some errors reduced in the coupled simulations

Next Steps• Resolve issue with land temperature bias• Complete 20+ year fully coupled simulation

(1989 to present) baseline simulationoEvaluation of baseline simulation

• Multi-decadal simulationsoRetrospectiveoFuture climateoRegional simulations for CORDEX / AR5

Next Steps• Implementation of additional climate

system componentso Ice sheetsoDynamic

vegetation