Sensitivity to the CAM candidate schemes in climate and forecast runs

along the Pacific Cross-section

Cécile Hannay, Dave Williamson, Jerry Olson, Jim Hack, Jeff Kiehl, Richard Neale and Chris Bretherton*

National Center for Atmospheric Research, Boulder *University of Washington, Seattle

AMWG, NCAR, 29-31 January 2007

Outline

•  The Pacific Cross Section

•  Models: PBL and convective schemes

•  Climate runs

- Model versus observations along the cross-section

•  Forecast runs

- Forecast runs settings

- Forecast errors along the cross-section

- Sensitivity to the 3 candidate deep convection schemes

- Sensitivity to the UW shallow convection/PBL schemes

•  Conclusion

The Pacific Cross-section

-  EUROCS project JJA 1998

-  GCSS intercomparison JJA 1998/2003

-  Observations ISCCP data

SSM/I product TOVS atmosphere

GPCP precipitation AIRS data

-  Reanalyses NCEP/ERA40

-  Pacific Cross-section: several cloud regimes stratocumulus, shallow cumulus, deep convection…

Models: PBL and convective schemes

Finite volume 1.9x2.5 26 vertical levels

Eulerian T42 30 vertical levels

Both resolution and dycore •  Control

•  Neale+Richter

•  Wu

•  Zhang

•  CAM-UW

Observations along the cross-section, JJA 1998

SWCF LWCF LWP

Low cloud Mid/high cloud Precipitation

CERES

CERES SSM/I

ISCCP, D1 GPCP ISCCP, D1

Climate runs versus observations, JJA 1998

SWCF LWCF LWP

Low cloud Mid/high cloud Precipitation

CERES

CERES SSM/I

ISCCP, D1

GPCP

ISCCP, D1

--- Obs --- Control --- Neale +Richter --- Zhang --- Wu

Climate runs versus observations

SWCF LWCF LWP

Low cloud Mid/high cloud Precipitation

CERES

CERES SSM/I

ISCCP, D1

GPCP

ISCCP, D1

--- Obs --- Control --- CAM-UW

Forecast run specification

•  Strategy If the model is initialized realistically, we assume the error comes from the parameterizations deficiencies.

•  Advantages Full feedback SCM Deterministic statistical Look at process level

•  Limitations Accuracy of the atmospheric state ?

Initialize realistically ERA40 reanalysis

CAM

5-day forecast Starting daily at 00 UT

Observations ERA40

Forecast errors and climate errors: Control-ERA40

•  Cloud regimes => range of error structures •  Climate bias appears very quickly in CAM •  Climate error ~ Forecast error at day 5

Forecast T error (K), day 1 Forecast T error (K), day 5 Climate T error (K), JJA1998

Forecast q error (g/kg), day 1 Forecast q error (g/kg), day 5 Climate q error (g/kg), JJA1998

ITCZ

Location on the cross-section

Sensitivity to the deep convection schemes

Forecast temperature errors at day 5, July 1998

All deep convection candidates •  Reduces warm T bias near ITCZ •  Error increases in the lower troposphere and above 300 mb. •  Changes in regions where the deep convection is not active

Control

Wu

Neale+ Richter

Zhang

ITCZ regime, forecast T error, July 1998

ITCZ region: forecast error is set within 1 day

Control

Warm bias

Neale+ Richter

Zhang Wu

Cold bias

ITCZ regime, temperature equation terms --- Control --- Neale +Richter --- Zhang --- Wu

Total tendency Advective tendency Physics tendency

�

∂T∂t

= −V •∇T −ω(∂T∂p

− RTpcp

) + Qphysics

ITCZ regime, physics tendency terms --- Control --- Neale+Richter --- Zhang --- Wu

Total physics Deep convection

PBL Radiation Prognostic cloud

Shallow convection

Deep convection tendency along cross-section

Control Neale+ Richter

Zhang Wu

ITCZ regime, Precipitation, July 1998 --- GPCP --- Control --- Neale+Richter --- Zhang --- Wu

- GPCP Dataset Daily precipitation

-  Control Loses water very quickly during day 1.

-  Wu and Zhang Strong diurnal cycle.

Total precipitation

Omega

ITCZ regime, omega at day 1, July 1998

--- Obs --- Control --- Neale +Richter --- Zhang --- Wu

Skill scores, July 1998 --- Control --- Neale+Richter --- Zhang --- Wu

V250, RMS error V850, RMS error

Tropics Tropics

Skill scores, July 1998 --- Control --- Neale+Richter --- Zhang --- Wu

North hemisphere

South hemisphere

SLP, RMS error Z500, RMS error

Stratocumulus

Location on the cross-section

Sensitivity to the UW scheme

Forecast temperature errors at day 5, JJA 1998

CAM-UW does not change much the error structure.

Control CAM-UW

Stratocumulus, moisture and PBL, JJA 1998

PBL height Specific humidity

Control

CAM-UW

Stronger daily cycle PBL collapses

day 0 day 1 day 2 day 5

Stratocumulus: timeseries of T and q error

TCAM-TERA40

qCAM-qERA40

Stratocumulus: q equation (single forecast)

Control

CAM-UW

q Advective tendency

Physics tendency

Stratocumulus regime (Physics terms)

Control

CAM-UW

PBL tendency

Shallow tendency

Prognostics cloud water tendency

Conclusion

•  CAM forecasts allows for diagnosing model errors in the different cloud regimes.

•  Climate bias appears very quickly –  Where deep convection is active, error is set within 1 day –  5-day errors are comparable to the mean climate errors.

•  Sensitivity to candidate parameterizations -  All deep convection schemes improve the warm bias in upper

troposphere, but cold bias increases in lower troposphere and near top of the model. Change the error where the deep convection is not active.

-  CAM-UW: does not change the error structure but CAM-UW operates very differently than Control at the process level.

Extra slides

Climate runs versus observations, JJA 1998

SWCF LWCF LWP

Low cloud Middle cloud High cloud

CERES

CERES SSM/I

ISCCP, D1 ISCCP, D1

--- Obs --- Control --- Neale --- Zhang --- Wu

ISCCP, D1

Climate errors: eulerian versus finite volume

FV T42

ITCZ regime: Cloud fraction

ITCZ regime, omega, July 1998

Control Neale+ Richter

Zhang Wu