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Attempts to improve distribution of boundary layer clouds in AFES
Akira Kuwano-Yoshida, Takeshi Enomoto and Wataru Ohfuchi
Earth Simulator Center, JAMSTEC, Japan
@Joint GCSS-GPCI/BLCI-RICO workshop,NASA/GISS, New York, USA,
18-21 September 2006
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Outline
1. Introduction of AFES2
2. Problems of clouds in AFES2
3. Improvements
4. Results
5. Summary
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AFES2• AGCM for Earth Simulator version 2 (Enomoto et
al. 2006)• Spectral, Eulerian and primitive-equation AGCM b
ased on CCSR/NIES AGCM 5.4.01• Vertical coordinates: Sigma = P/Ps• Convection: Emanuel (1991) scheme• Grid condensation: Le Treut and Li (1991) & Smit
h (1990)• Cumulus cloud fraction: Teixeira and Hogan (200
2) (but 2D fraction, not 3D)• Vertical diffusion: Mellor-Yamada level 2
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• Final object of our group is to try seasonal prediction experiments using a high resolution coupled AOGCM (CFES, Atmos. : T239 and Ocean: 0.25 degree, Komori et al. 2006).
• But, there are some many biases in AFES2, especially for clouds, and lead to ocean biases when coupled simulation.
Motivation
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• A book including AFES2 and CFES descriptions and biases will be published soon from Springer@Spring St. Broadway.
• You can reserve @ www.amazon.com
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• Wataru, who is a tally of the editors and our group leader, is writing its introduction.
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This study
• To test a new grid scale condensation using GPCI setting.
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AFES original grid scale condensation
• Statistical method by Uniform (Top Hat) PDF (Le Treut and Li 1991).
• A PDF’s standard deviation is proportional to Blackadar (1962) mixing length.
• This is same as the IPCC model.
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Low cloud fraction : JJA 1998
ISCCP AFES2 T79L72
•Too much clouds around Antarctic and over Arctic•Less over Southeastern Pacific and southern Indian Ocean
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New scheme
• Yamada and Mellor (1979) scheme with gaussian PDF.
• Standard deviation of PDF is diagnosed by Mellor-Yamada Level 2 scheme.
• Non-local mixing length (Sun and Chang 1986) is used within boundary layer.
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Model Setting
• Resolution:– T79L72 (about 1.5 degree, 26 layers within
0.7 – 1 sigma)– T79L96 (50 layers within 0.7 - 1 sigma)– T239L96 (about 0.5 degree)
• Initial condition: – JRA25 data (1.25 degree) provided by JMA
• SST:– NOAA OISST (1 degree weekly)
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Comparison in GPCI region
• 4 cases are compared at JJA 1998.– T79L72OLD– T79L72NEW– T79L96NEW– T239L96NEW
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OLD versus NEW
Clouds around Antarctic become better.But, clouds are less over southern Pacific and Atlantic..
T79L72OLD T79L72NEW
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Why?
• Standard deviation estimated by turbulent scheme is too small, because vertical resolution is coarser than 100 m.
• So, we tried 96 layers, which has 50 layers within 0.7 – 1 sigma which is 2 times more than in 72 layers.
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L72 NEW L96 NEW
ISCCP L72 OLD
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Impact of Horizontal Resolution
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T79L96NEW T239L96NEW
ISCCP
Cloud locations become better
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PRECIPITATIONT72L96NEW T239L96NEW
GPCP
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Detailed topography makes more real wind field.
U10, V10, mag(U10, V10), Topography
T79L96NEW T239L96NEW
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Cross sections
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Cloud fraction become better, but cloud water is less than observation.
So, effect on surface shortwave radiation is small.
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Other problemsT239L96NEW ISCCP
HIGH CLOUD
MIDDLECLOUD
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JJA 1998-2003 average
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Summary
• New grid condensation scheme needs higher vertical resolution < 100 m, not only for estimating standard deviation of PDF but also vertical mixing making better boundary layer structure.
• Higher horizontal resolution with detailed topography makes more realistic 3D wind fields and results in improvements of clouds and precipitation locations.
• Biases of much high cloud and less middle cloud still remain.