Transcript CCSM3.5+ Coupled Experiments Rich Neale Phil Rasch, Cecile Hannay, Jon Wolfe, Steve Yeager Experiments 1. 2. 3. The University of Washington (UW) Boundary layer and shallow convection parameterizations 0.5 degree CAM.

CCSM3.5+ Coupled
Experiments
Rich Neale
Phil Rasch, Cecile Hannay,
Jon Wolfe, Steve Yeager
Experiments
1.
2.
3.
The University of Washington (UW) Boundary
layer and shallow convection
parameterizations
0.5 degree CAM climate projection scoping
exercise
Development experiments with an additional
20-m thick atmosphere model layer at the
surface
Results are very preliminary!
1. UW-CCSM3.5

Planentary Boundary Layer (PBL)




Shallow convection (ShCu)



UW diagnostic TKE scheme (Grenier, Bretherton,
Park) replaces existing Holtslag-Boville (HB) scheme
Improved treatment of cloud topped boundary layers
Stability-based marine stratus calculation removed
UW scheme (McCaa, Bretherton, Grenier) replaces 3level Hack adjustment scheme
Scheme closes on inhibition and TKE from PBL
scheme
UW requires 30 vertical levels compared to 26
for HB (4 extra layers in PBL)
Low cloud fraction (%)
CAM3.5
Warren annual low
cloud
Total
Difference
CAM3.5 - HB
CAM3.5 - HB
error
CAM3.5 - UW
CAM3.5 - UW
error
SW cloud forcing (Wm-2)
CAM3.5
CERES SWCF
Total
Difference
CAM3.5 - HB
CAM3.5 - HB
error
CAM3.5 - UW
CAM3.5 - UW
error
Low cloud fraction (%)
CCSM3.5
Warren annual low
cloud
Total
Difference
CCSM3.5 - UW
CCSM3.5 - UW
error
CAM3.5 - UW
CAM3.5 - UW
error
SW cloud forcing (Wm-2)
CCSM3.5
CERES SWCF
Total
Difference
CCSM3.5 - UW
CCSM3.5 - UW
error
CAM3.5 - UW
CAM3.5 - UW
error
East Pacific SST seasonal cycle
HB-CCSM3.5
UW-CCSM3.5
HadISST
East Pacific SWCF seasonal cycle
HB-CCSM3.5
5N-5S
HadISST
UW-CCSM3.5
ENSO
nino3.4 statistics
HadiSST
HB-CCSM3.5
Note different
scales
Events peak in
February
UW-CCSM3.5
HadISST
HB-CCSM3.5
UW-CCSM3.5
ENSO
teleconnections
Nino3 SSTA lag-0
correlation
UW-CCSM3.5
HB-CCSM3.5
Competitive
coupled
climate
Taylor Diagram Metrics
Radial direction – variance
Angle - correlation
2. High-Res CAM – CCSM3.5


CCSM advisory board encouraged high resolution
short-term ‘climate projections’
AIM: Provide greater detail on shorter timescales (a
couple of decades) before GHG emission scenarios
diverge significantly
0.5 degree atmosphere with 1 deg (nominal) ocean
 Maintain 2 degree physics timestep (30 minutes)
 1980-2000 initial spin-up period (done)
 Greenhouse gas + aerosol forcings
 2001-2030 projection period (to do)

Benefits of higher resolution
Rainfall (DJF)
Rainfall (JJA)
GPCP Rainfall
mm/day (JJA)
Asian Monsoon + ITCZ
Monsoon rainfall
focused closer to
orography
2 degree
GPCP
0.5 degree
GPCP
Twin ITCZ
remains
2 degree
0.5 degree
East Pacific SST seasonal cycle
2 degree
5N-5S
HadISST
0.5 degree
Surface Stress
5N-5S
2 degree minus ERS stress
0.5 degree minus ERS stress
ENSO
nino3 SSTA statistics (1980-1999)
2 degree
0.5 degree
HadISST
ENSO
teleconnections
2 deg
0.5 deg
Nino3 SSTA lag-0
correlation
3. 20-m layer CAM – CCSM3.5
20-m thick layer next
to the surface
 Leads to improved
surface flux
calculations
 Surface flux averaging
required to stabilize
simulation and to use
same CAM timestep

20m
West Pacific Rainfall
GPCP Rainfall (JJA) mm/day
HB-CAM3.5
20m-CAM3.5
East Pacific SST seasonal cycle
HB-CCSM3.5
5N-5S
HadISST
20m-CCSM3.5
ENSO
nino3.4 statistics
HadiSST
Note different
scales
UW-CCSM3.5
20m-CCSM3.5
Summary

UW CCSM3.5






High Resolution CAM CCSM3.5






Short-term/high resolution climate projection scoping exercise
Improved North American mean climate
Better defined monsoonal features; twin ITCZ remains
East Pacific SST semi-annual -> annual cycle shift
ENSO characteristics maintained from lower resolution
20-m thick layer CAM CCSM3.5






UW scheme provides improved moist PBL (cloud-topped)
Inclusion of UW PBL-ShCu scheme gives a stable coupled climate
More favorable SCu location; excessive SWCF
East Pacific SST semi-annual -> annual cycle shift
ENSO period 4-7 years; excessive amplitude
Improved representation of surface stability/flux characteristics
Significant changes in mean climate
Favorable location shift; excessive seasonal cycle
East Pacific SST semi-annual -> annual cycle shift
ENSO period >4 years; weak amplitude
Preliminary results!