John J. Cassano, Matthew Higgins, Alice DuVivier
University of Colorado
Wieslaw Maslowski, William Gutowski, Dennis Lettenmaier, Andrew Roberts
Project goals
 Develop 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 system
 Small-scale features in the atmosphere can have
large impacts on climatically important processes
such as:
 Cyclone intensity / polar lows
 Mesoscale features such as topographically forced winds
(Greenland tip jets)
 Realistic representation of these processes is
critical for improved climate projection
Cyclone Intensity and Size
 Resolution 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 human
activities 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)
WRF Tip Jet Case
Observed and Modeled Wind Speed
a)
b)
c)
d)
e)
Two Month: WRF average latent heat flux
a)
b)
c)
d)
Two Month: WRF 95th percentile latent heat flux
a)
b)
c)
d)
RACM simulations
 Coupled: Regional Arctic Climate Model (RACM)
 WRF – POP – CICE - VIC
 Simulation from 1989 to 2002 (currently)
 Atmosphere – land : WRF – Noah
 CORDEX simulation from 1989 to 2009
 RACM and WRF simulations forced with:
 ERA-Interim IBC/LBCs
 Observed sea ice
 Use 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)
Sea Level Pressure
1989-2002 DJF Climatology
ERA-Interim
RACM
WRF
ERA-Interim & RACM
RACM – ERA-Interim
WRF – ERA-Interim
Sea Level Pressure
1989-2002 JJA Climatology
ERA-Interim
ERA-Interim & RACM
RACM
WRF
RACM – ERA-Interim
WRF – ERA-Interim
SLP and Sea Ice
1989-2002 JJA Climatology
ERA-Interim
ERA-Interim & RACM
RACM
RACM – ERA-Interim
RACM - NSIDC
Near Surface Temperature
1989-2002 JJA and DJF Climatology
RACM – ERA-Interim JJA
WRF – ERA-Interim JJA
RACM – ERA-Interim DJF
WRF – ERA-Interim DJF
Temperature Profiles
Northern Alaska
1989-2002 DJF Climatology
Height
RACM – ERA-Interim DJF
WRF
RACM
Temperature
Part of Russia
Height
Height
North of 80 Latitude
WRF
RACM
Temperature
WRF
RACM
Temperature
Precipitation and Snow Cover
1989-2002 DJF Climatology
RACM – ERA-Interim DJF
WRF – ERA-Interim DJF
RACM – WRF DJF
Precipitation Difference (%)
RACM – ERA-Interim DJF
WRF – ERA-Interim DJF
Snow Water Equivalent Difference (kg m-2)
RACM – WRF DJF
Conclusions
 Use RASM to explore the impact of small-scale
atmospheric processes on the coupled climate system
 Greenland tip jet showed large change in surface heat
fluxes with increased resolution
 Care must be taken when coupling model components
 Precipitation problem in early versions of RACM
 Current version of RACM is stable
 Errors 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 simulation
o Evaluation of baseline simulation
• Multi-decadal simulations
o Retrospective
o Future climate
o Regional simulations for CORDEX / AR5
Next Steps
• Implementation
of additional
system components
o Ice sheets
o Dynamic
vegetation
climate