CSIRO Marine and Atmospheric Research 1 CCAM simulations for CORDEX South Asia John McGregor, Vidya Veldore, Marcus Thatcher, Peter Hoffmann, Jack Katzfey and Kim Nguyen CSIRO Marine and Atmospheric Research Aspendale, Melbourne CORDEX Workshop Kathmandu 28 August 2013
CCAM simulations for CORDEX South Asia. John McGregor, Vidya Veldore, Marcus Thatcher, Peter Hoffmann, Jack Katzfey and Kim Nguyen CSIRO Marine and Atmospheric Research Aspendale, Melbourne CORDEX Workshop Kathmandu 28 August 2013. Introduction to the downscaling approach GCM selection - PowerPoint PPT Presentation
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CSIRO Marine and Atmospheric Research 1
CCAM simulations for CORDEX South Asia
John McGregor, Vidya Veldore, Marcus Thatcher, Peter Hoffmann, Jack Katzfey and Kim Nguyen
CSIRO Marine and Atmospheric ResearchAspendale, Melbourne
CORDEX WorkshopKathmandu
28 August 2013
CSIRO Marine and Atmospheric Research
Outline
• Introduction to the downscaling approach
• GCM selection
• SST bias correction
• CCAM model features
• Behaviour of the simulations
CSIRO Marine and Atmospheric Research
Downscaling with CCAM
CCAM (~50 km)
CCAM (~14 km)
Bias correction
GCM (~200 km)
GCM SST/Sea-ice
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Quasi-uniform C192 CCAM grid with resolution about 50 km, showing every 4th grid point
Stretched C96 grid with resolution about 14 km over Nepal, showing every 2nd grid point
• The 50 km run is then downscaled to 10 km by running CCAM with a stretched grid, but applying a digital filter every 6 h to preserve large-scale patterns of the 50 km run
• A separate 100 km global CCAM run is also used to drive RegCM4.2 at its boundaries for 20 km RCM runs
CCAM downscaling methodology
• Coupled GCMs have coarse resolution, but also possess Sea Surface Temperature (SST) biases such as the equatorial “cold tongue”
• We first run a quasi-uniform 50 km global CCAM run driven by the bias-corrected SSTs
CSIRO Marine and Atmospheric Research
Indonesia 14 km
Some previous CCAM downscaling projects
Pacific Islands 60 km and 8 km
South Africa
Australia20 km – 60 km
Tasmania8 km – 14 km
CSIRO Marine and Atmospheric ResearchGCM Selection | Peter
Hoffmann
GCM Selection
CSIRO Marine and Atmospheric Research
GCM Selection Requirements
• Good performance in present climate• Simulation of rainfall, air temperature etc.
• Reproduce observed trends
• Good SSTs• ENSO pattern/frequency
• SST distribution
• Good spread of climate change signals
GCM Selection | Peter Hoffmann
CSIRO Marine and Atmospheric Research
GCM Selection Evaluation studies
• 24 CMIP5 models
• > 20 evaluation studies
• 6 publications with rankings + evaluation used within the Vietnam project
• Peer-reviewed or submitted
GCM Selection | Peter Hoffmann
ACCESS1.0ACCESS1.3CanESM2
CCSM4CNRM-CMS
CSIRO-Mk3-6-0FGOALS-g2FGOALS-s2GFDL-CM3
GFDL-ESM2MGISS-E2-HHadCM3
HadGEM2-CCHadGEM2-ES
inmcm4IPSL-CM5A-LRIPSL-CM5A-MR
MIROC4hMIROC5
MIROC-ESM MIROC-ESM-CHEM
MPI-ESM-LRMRI-CGCM3NorESM1-M
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GCM Selection Example: performance in current climate over Indochina
The rankings of the 6 individual studies are averaged to yield a final ranking of the models.
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GCM SelectionClimate change signal JJA - good spread
X
XX
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SST correction
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• Observations• daily optimum interpolation SST & SIC (Reynolds et al.,
2007)
• 1/4° resolution for 1982-2011
• Method
adjust variance adjust mean
OBS
GCM
SST
freq
uenc
y
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SST bias correction Results: SST BIAS ACCESS1.0
JAN JUL
original
after correction
(K)
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Results: SST variance ACCESS1.0 (January)
ACCESS1.0 ObservedBias & Variance
corrected
Mean SSTs
SST Stdev
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The conformal-cubic atmospheric model
• CCAM is formulated on the conformal-cubic grid
• Orthogonal• Isotropic
Example of quasi-uniform C48 grid with resolution about 200 km
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Variable-resolution conformal-cubic grid The C-C grid is moved to locate panel 1 over the region of interestThe Schmidt (1975) transformation is applied
- it preserves the orthogonality and isotropy of the grid- same primitive equations, but with modified values of map
factor
C48 grid (with resolution about 20 km over Vietnam
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CCAM dynamics
• atmospheric GCM with variable resolution (using the Schmidt transformation)
- produces good dispersion properties• a posteriori conservation of mass and moisture
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CCAM physics• Cumulus convection:scheme for
simulating rainfall processes
• Detailed modelling of water vapour, liquid and ice to determine cloud patterns
CSIRO Marine and Atmospheric Research
CCAM physics• Cumulus convection:scheme for
simulating rainfall processes
• Detailed modelling of water vapour, liquid and ice to determine cloud patterns
• Parameterization of turbulent boundary layer (near Earth’s surface)
CSIRO Marine and Atmospheric Research
CCAM physics• Cumulus convection:scheme for
simulating rainfall processes
• Detailed modelling of water vapour, liquid and ice to determine cloud patterns
• Parameterization of turbulent boundary layer (near Earth’s surface)
• Modelling of vegetation and using 6 layers for soil temperatures and moisture
• CABLE canopy scheme
CSIRO Marine and Atmospheric Research
CCAM physics
• Cumulus convection:scheme for simulating rainfall processes
• Detailed modelling of water vapour, liquid and ice to determine cloud patterns
• Parameterization of turbulent boundary layer (near Earth’s surface)
• Modelling of vegetation and using 6 layers for soil temperatures and moisture. 3 layers for snow
• CABLE canopy scheme
• GFDL parameterization of radiation (incoming from sun, outgoing from surface and the atmosphere)
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Cumulus parameterization• In each convecting grid square there is an upward
mass flux within a saturated aggregated plume• There is compensating subsidence of environmental
air in each grid square• As for Arakawa schemes, the formulation is in terms
of the dry static energy
sk = cpTk + gzk
and the moist static energy
hk = sk + Lqk
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Above cloud base
plume
detrainment
downdraft
subsidence
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Enhancements for Maritime Continent
The Maritime Continent has many islands with land or sea breeze effects, and extra SST variability
a) enhance sub-grid cloud-base moisture if diurnal increase of SSTs, or
b) enhance sub-grid cloud-base moisture if upwards vertical motion
Both (a) and (b) are beneficial over Indonesia, Australia, Vietnam, China – (b) slightly better
(b) seems less suitable over India
(a) still fine over India
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Cloud microphysics scheme (Rotstayn)CCAM carries and advects mixing ratios of
water vapour (qg), cloud liquid water (ql) and cloud ice water (qi)
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Latest GFDL radiation scheme
• Provides direct and diffuse components
• Interactive cloud distributions are determined by the liquid- and ice-water scheme of Rotstayn (1997). The simulations also include the scheme of Rotstayn and Lohmann (2002) for the direct and indirect effects of sulphate aerosol