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

Outline

1. Introduction of AFES2

2. Problems of clouds in AFES2

3. Improvements

4. Results

5. Summary

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

• 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.

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• Wataru, who is a tally of the editors and our group leader, is writing its introduction.

This study

• To test a new grid scale condensation using GPCI setting.

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.

Low cloud fraction : JJA 1998

ISCCP AFES2 T79L72

•Too much clouds around Antarctic and over Arctic•Less over Southeastern Pacific and southern Indian Ocean

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.

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)

Comparison in GPCI region

• 4 cases are compared at JJA 1998.– T79L72OLD– T79L72NEW– T79L96NEW– T239L96NEW

OLD versus NEW

Clouds around Antarctic become better.But, clouds are less over southern Pacific and Atlantic..

T79L72OLD T79L72NEW

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.

L72 NEW L96 NEW

ISCCP L72 OLD

Impact of Horizontal Resolution

T79L96NEW T239L96NEW

ISCCP

Cloud locations become better

PRECIPITATIONT72L96NEW T239L96NEW

GPCP

Detailed topography makes more real wind field.

U10, V10, mag(U10, V10), Topography

T79L96NEW T239L96NEW

Cross sections

Cloud fraction become better, but cloud water is less than observation.

So, effect on surface shortwave radiation is small.

Other problemsT239L96NEW ISCCP

HIGH CLOUD

MIDDLECLOUD

JJA 1998-2003 average

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.