working group on numerical experimentation - wgne mike/ape/ m. blackburn 1, b. j. hoskins 1,2, d. l....

Working Group on Numerical Experimentation - WGNE http://www.met.reading.ac.uk/~mike/APE/

M. Blackburn1, B. J. Hoskins1,2, D. L. Williamson3, Y-Y. Hayashi4 and K. Nakajima5

&14 APE Modelling Groups

1. NCAS-Climate, University of Reading, UK;2. Imperial College, London and University of Reading, UK;3. National Center for Atmospheric Research, Boulder, USA;4. Kobe University, Japan;5. Kyushu University, Fukuoka, Japan

Comparison of Atmospheric GCM Simulations on a

Water-Covered Earth

- MOCA-09 J11 Climate Model Intercomparison 24 July 2009 -


• Experiment aims and configuration

• Participating groups and models

• Aspects of model intercomparison:

• Future plans

• Wider context

Talk outline

Tropical mean state – dependence on SST profile

Tropical variability

(Response to localised SST anomaly)

Global energy balance


APE Experimental Design (1)

• Complete AGCMs but idealised planet

• More constrained experiment than real-world benchmark (AMIP)

• Investigate sensitivity to tropical SST profile – with reference to theoretical limits (Held & Hou, 1980)

• Zonally symmetric forcing – unconstrained wave evolution

• Convective organisation and remote response to tropical SST anomalies

• Facilitate understanding of model differences and sensitivities


APE Experimental Design (2)

• No land / orography

• 8 idealised sea surface temperature (SST) distributions

• 5 symmetric SSTs span a range of tropical climates

• Local and global-scale SST anomalies

• 3-year climate (following spin-up)

• Following Neale & Hoskins (2000)

• Specified solar forcing, O3, GHG etc

Symmetric SST profiles

SST anomaly experiments

3KW1

1KEQ 3KEQ


APE Modelling Groups

Group Location Model Resoln Features

AGU for APE Japan (consortium) AFES v.1.15 T39 L48 Spectral, eulerian

CGAM Reading, UK HadAM3 N48 L30 3.75º x 2.5º grid

CSIRO Aspendale, Australia CCAM-4-12 C48 L18 ~220km conformal cubic grid

DWD Mainz, Germany GME 29.1.1 ni=64 L31 ~1º icosahedral-hexagonal grid

ECMWF Reading, UK IFS 29r2 / 32r3 TL159 L60 Spectral, semi-lagrangian

FRCGC Yokohama, Japan NICAM 7km L54 icosahedral grid, non-hydrostatic

GFDL Princeton, USA AM2p14 N72 L24 2.5º x 2º grid (IPCC)

GSFC Maryland, USA NSIPP-1 N48 L34 3.75º x 3º grid

K1-Japan Japan (collaboration) CCSR/NIES 5.7 T42 L20 s-l moisture and cloud

LASG Beijing, China SAMIL R42 L9 Spectral, eulerian

MIT Cambridge, USA MIT-gcm C32 L40 ~280km cubed sphere

MRI Tokyo, Japan MRI/JMA98 T42 L30 Spectral, eulerian

NCAR Boulder, USA CCSM-CAM3 T42 L26 Spectral, eulerian

UKMO Exeter, UK pre-HadGAM1 N96 L38 1.875º x 1.25º, semi-lagrangian


Precipitation response to SST

• Regime transition: single double ITCZ

• Transition occurs close to Qobs profile (based on tropical Pacific)

• Accurate tropical simulation of the real Earth may be particularly difficult to achieve

Control QobsPeaked

Flat


Precipitation (mm/day)

Temperature (K)

Omega (Pa s-1)

Rel. Humidity (%)

Zonal wind (m s-1)

ECMWF GSFC CSIRO

Qobs – control differences


Impacts

• Cools the tropics (deep convection over cooler SST, fixes tropical θe profile)

• Widens Hadley Cell

• Displaces the jets polewards

Qobs - control

• Large uncertainty due to transition / no-transition

• Consistency between degree of transition and strength of tropical and extratropical response

Outliers (CSIRO, LASG):

• Weak splitting of ITCZ but strong response

• Due to increase in sub-tropical precipitation?

ITCZ Regime Transition


Inter-tropical Convergence Zone

• When does convection break through the trade-wind inversion?

• Many interacting processes

• ITCZ location sensitive to all these processes in models

Emanuel (1994)

[ Evap – Precip ] Surface Wind ECMWF - APE control (time average)

(mm/day)Cool 30º lat.

Eq. Warm


Hydrological Cycle: NCAR model

Williamson (2008)

Precipitation: contributions to resolution dependence, T42 / T85

params.

timestep grid

Truncn. diffusion

params.at T42


Tropical Wave Spectra (control)

Log-power of symmetric modes of equatorial precipitation (10°N - 10°S average)


Tropical Wave Spectra (ECMWF)

• Recent model includes major convection changes (cy32r3, November 2007)

• Precipitation organised strongly in equatorial waves

• MJO for Qobs?see Bechtold et al (2008)


• Global energy balance unknown

• Mean ~15 Wm-2 down

• TOA imbalance goes into ocean (fixed SST)

• TOA spread >30 Wm-2

• Dominated by cloud (fraction + reflectivity)

• Compensation of land / ocean biases for real-Earth global balance?

Global Energy Balance (control)


• Currently completing diagnostic analysis & writing papers

• Special Issue of J. Met. Soc. Japan (published 2010)

• APE Atlas – comprehensive intercomparison plots (online)

• Data archive made public (~end 2009)

APE – Status & Plans


• Comparison of climate and NWP models in idealised configuration

• Wide variety of behaviour despite idealised setting

• Transition from single to split ITCZ close to Earth-like SST profile

• Tropical wave spectrum not converged at typical climate resolutions

• Large uncertainty in global energy balance (compensating biases?)

• “Correct” behaviour unknown, but reveals uncertainties

• Augment with single-model sensitivity + constrained experiments

• Addition to the experimental hierarchy

• Use as a process-study test-bed

• Talks in M10 Tropical Circulation (MOCA-09 week 2)

APE – Conclusions / Context


Evaluation of Atmospheric GCMs- an experimental hierarchy -

1D / 2D idealised flows

Dynamical core

Idealised moist core Aqua-planet AMIP

•Full complexity GCM

- unique dynamics

- unique moist parameterizations

•Difficult to isolate reasons for differences

•Aqua-planet idealises the planet, not the model!

•Dry dynamics

- linear relaxation to climatology

- Rayleigh friction boundary layer

•Unrealistic sensitivities?

•Aim for

- single idealised moist parameterization

- minimal complexity to represent processes

•Use in all dynamical cores

•Sensitivity of a moist atmosphere to dynamical formulation

•Frierson et al (2006,2007)


Use as a Process-Study Test-bed• Idealised configurations useful for process studies

• Main use of the Held-Suarez Dynamical Core

• Aqua-Planet examples:

1. Partition response to CO2 forcing 2. Ingredients of Atlantic storm-track

Response to uniform or polar SST increase

Kodama & Iwasaki (2009, JAS, in press)

[T]

[u]

Brayshaw et al (2009, JAS, in press)

Zonal wind

250hPa (colour)

850hPa (contour)

SST (contour)

Continents

“Rockies”


• Large spread in albedo

• Due to cloud – both fraction + reflectivity

• e.g. UKMO, MRI high albedo but low fraction

Global Energy Balance


Insolation

• Theoretical: sw_toai = (S0/π) * cos(lat)

• Several models are near identical, with equatorial peak S0/ π =434.493 Wm-2

• Scaling, timing, polar issues

working group on numerical experimentation - wgne mike/ape/ m. blackburn 1, b. j. hoskins 1,2, d. l....

Documents

working group

tropical sst profile

tropical sst anomalies

keq slide

t42 slide

strength of tropical

warm slide

flat slide