Forcing BAM With HADISST1.1 for the Period 1948-2002

S. Grainger, C.S. Frederiksen and

J.M. Sisson

 Bureau of Meteorology Research Centre, Melbourne, Australia

Acknowledgements: Z. Sun (BMRC), B. McAvaney (BMRC), X. Zheng (NIWA)

Contents

• Overview of BAM

• General results

• South-West Western Australia

• Interannual variability over Australia

• Conclusions

BAM Climate Model

• T47L17 Spectral Model ( = 0.991 to 0.0089)• Sun – Edwards – Slingo radiation scheme

(allows for aerosols)• Prognostic clouds (CSIRO – Rotstayn)• Mass-flux convection• CHASM Land Surface Scheme

C20C Forcings

• HADISST 1.1 SST and sea-ice distribution– Sea-ice is on/off in BAM

• CO2 from lookup table

• SPARC ozone trend after 1975• Stratospheric volcanic aerosol time series• Tropospheric aerosol climatology (GADS)• Time-varying solar orbital parameters

– Solar Constant is fixed

• Initialised at 0Z 1 January 1948– IC 0Z 1-10 January 1988 from AMIP run

Status

• Experiment 2– 9.8 ensemble members completed– Presenting results from SIX (6) members– Time series and standard diagnostics to be placed

on Bureau DODS server “soon”

• Experiment 0– To be started 2nd Quarter 2004

• Experiment 1– Not yet started

MSLP DJF Climatology (1950 – 2002)

NCEP

C20C (6)

C20C MSLP DJF Standard Deviation (hPa)

C20C MSLP DJF External Variability Ratio

DJF

JJA

Correlation (C20C Z500, Nino3 SST)

• Sudden decrease in early winter (MJJ) rainfall in late 1960’s– Affects Perth water supply, land-use and the

environment

• Appears to be caused by changes in large-scale weather patterns– Changes can be seen in, eg, NCEP reanalysis– Is it anthropogenic?

South-West Western Australia (SWWA)

Australia

Rottnest Island early winter (May-July) rainfall

IOCI (2002)

Correlations

C20C – NCEP = 0.228

C20C – obs. = -0.239

NCEP – obs. = 0.223

MSLP JJA Difference (1975-1999) – (1950-1974)

NCEP

C20C (6)

U200 JJA Climatology

NCEP

1950 - 1974 1975 - 1999

C20C (6)

U200 JJA Difference (1975-1999) – (1950-1974)

NCEP

C20C (6)

Interannual variability over Australia

• Use technique of Zheng et al. (J. Clim. 2000)– More details in Carsten Frederiksen’s presentation

on Tuesday

• Monthly means for each month in season• Generate intraseasonal, and slow internal

and external interannual variability contributions

Australian Surface Air Temperature Variability - DJF

Nce

p

Total Intraseasonal Slow-Predictable

BA

M3

Australian Surface Air Temperature Variability - DJF

External Slow-Predictable Internal Slow-Predictable

BAM3 Slow-Predictable

Australian Surface Air Temperature Variability - DJF

Correlations BAM3 vs NCEP

Total vs Total External vs Total External vs Slow-Predictable

Conclusions

• BAM reproduces many aspects of the climate of the 20th Century– Responds well to SST forcing– Is able to capture many aspects of

interannual variability

• BAM does less well at reproducing climate changes– There is little apparent response to

changes in radiative forcings