1. 1 Aiguo DAI National Center for Atmospheric Research, Boulder, CO, USA The 20 th century East Asian summer monsoon simulated by coupled climate models of IPCC AR4 Tianjun ZHOU LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China E-mail: zhoutj@lasg.iap.ac.cn 4th International CLIVAR Climate of the 20th Century Workshop, 13-15th March 2007 Hadley Centre for Climate Change, Exeter, UK

2. 2 Outline  Background  Data description  Evaluation of the mean states over E. Asia  Decadal variability of the EASM  Summary

3. 3 Background  About 25% of humanity inhabits the region of the East Asian monsoon. The economy and society across the region are greatly influenced by the evolution and variability of the monsoon.  The East Asian monsoon climate exhibits variability on a variety of time scales.  While the interaction of Asian monsoon with the ENSO is well understood, the monsoon interdecadal variability is less well documented and its underlying mechanism is poorly understood.

4. 4 Data and Approach  We analyze the outputs of the 20th century climate simulations (20C3M) of IPCC AR4 coupled models to validate the realism of current state-of-the-art coupled GCMs in catching the present climate over East Asia.  We use the model data, combined with observational evidences, to address the question of whether the prescribed external forcing agents have played key roles in the variability of the East Asian monsoon climate in the 20th century.  Particularly, we want to know the extent to which the 20th century coupled model integrations can reproduce the interdecadal variability of the East Asian summer monsoon (EASM), with a special focus on the recent (1950-1999) weakening of the EASM, before we apply them to study the underlying mechanisms.

5. 5  20 th Century Climate in Coupled Models (20C3M). Coordinated by WG1 of IPCC AR4.  The 20 th century climate simulations are made with various combinations of forcings including greenhouse gases (GHGs), sulfate aerosol effects, and ozone, as well as volcanic aerosols and solar variability.  Outputs of 23 coupled models are used in the analyses. DATA: 20C3M of IPCC AR4 Zhou Tianjun and Rucong Yu, 2006, Twentieth Century Surface Air Temperature over China and the Globe Simulated by Coupled Climate Models, Journal of Climate, 19(22), 5843-5858.

6. 6 East Asian summer monsoon components (Figure from Ding Yihui) Two Key Parts: WPSH: Z500 EA Jet: U200 Zhou Tianjun, Zhaoxin Li, 2002, Simulation of the east Asian summer monsoon by using a variable resolution atmospheric GCM, Climate Dynamics, 19:167-180 Zhou, T.-J., and R.-C. Yu (2005), Atmospheric water vapor transport associated with typical anomalous summer rainfall patterns in China, J. Geophys. Res., 10, D08104, doi:10.1029/ 2004JD005413 Zhang, Y., X. Kuang, W. Guo, and T. Zhou, 2006, Seasonal evolution of the upper- tropospheric westerly jet core over East Asia, Geophys. Res. Lett., 33, L11708, doi:10.1029/2006GL026377

7. 7 The realism of coupled GCMs in catching the present climate (1979-1999 JJA state)?  Western Pacific subtropical high (Z500)  East Asian westerly jet (U200)  Rainfall Assessed by using Taylor Diagram EAR40 is used as Observation. Precipitation Data from GPCP.

8. 8 Western Pacific subtropical high (Z500), JJA Shaded: Values lager than 5870 gpm

9. 9 Western Pacific subtropical high (Z500), JJA (1) bccr_bcm2_0 (2) cccma_cgcm3_1 (3) cccma_cgcm3_1_t63 (4) cnrm_cm3 (5) csiro_mk3_0 (6) gfdl_cm2_0 (7) gfdl_cm2_1 (8) giss_aom (9) giss_model_e_h (10) giss_model_e_r (11) iap_fgoals1_0_g (12) inmcm3_0 (13) ipsl_cm4 (14) miroc3_2_hires (15) miroc3_2_medres (16) mpi_echam5 (17) mri_cgcm2_3_2a (18) ncar_ccsm3_0 (19) ncar_pcm1 (20) ukmo_hadcm3 (21) ukmo_hadgem1

10. 10 East Asian JJA westerly jet (U200)

11. 11 (1) bccr_bcm2_0 (2) cccma_cgcm3_1 (3) cccma_cgcm3_1_t63 (4) cnrm_cm3 (5) csiro_mk3_0 (6) gfdl_cm2_0 (7) gfdl_cm2_1 (8) giss_aom (9) giss_model_e_h (10) giss_model_e_r (11) iap_fgoals1_0_g (12) inmcm3_0 (13) ipsl_cm4 (14) miroc3_2_hires (15) miroc3_2_medres (16) mpi_echam5 (17) mri_cgcm2_3_2a (18) ncar_ccsm3_0 (19) ncar_pcm1 (20) ukmo_hadcm3 (21) ukmo_hadgem1 East Asian JJA westerly jet (U200)

12. 12 JJA Rainfall

13. 13 (1) bcc_cm1 (2) bccr_bcm2_0 (3) cccma_cgcm3_1 (4) cccma_cgcm3_1_t63 (5) cnrm_cm3 (6) csiro_mk3_0 (7) gfdl_cm2_0 (8) gfdl_cm2_1 (9) giss_aom (10) giss_model_e_h (11) giss_model_e_r (12) iap_fgoals1_0_g (13) inmcm3_0 (14) ipsl_cm4 (15) miroc3_2_hires (16) miroc3_2_medres (17) mpi_echam5 (18) mri_cgcm2_3_2a (19) ncar_ccsm3_0 (20) ncar_pcm1 (21) ukmo_hadcm3 (22) ukmo_hadgem1 JJA Rainfall

14. 14 Weakened EASM in Rain Gauge Data JJA trend in unit of cm/50a from 1958-2000 Normalized time series of JJA precipitation averaged over the Yangtze River and Yellow River

15. 15 Weakened EASM Index in Observations An EASM index is defined as the summation of SLP difference between 110  E and 160  E from 10  N to 50  N. The SLP gradient between the land and the sea for each year is then divided by its climate mean value (hereinafter EASM index)

16. 16 EASM index in Coupled Models Red line is the observation

17. 17 Correlation coefficients between the simulated and the observed EASM Index on decadal time scale. Model Correlation coefficients 1880-19991900-19491950-1999 BCCR-BCM2 0.19-0.30.13 CCSM3 -0.13-0.40.44 CGCM3.1(T47) 0.310.020.37 CGCM3.1(T63) -0.250.04-0.41 CNRM-CM3 -0.39-0.16-0.63 CSIRO-Mk3.0 0.020.400.20 ECHAM5/MPI-OM -0.26-0.33-0.26 ECHO-G -0.03-0.30-0.16 FGOALS-g1.0 -0.25-0.40-0.27 GFDL-CM2.0 -0.08-0.320.41 GFDL-CM2.1 0.380.130.73 GISS_AOM 0.250.080.24 GISS_EH 0.230.200.03 GISS_ER 0.160.270.45 INM-CM3.0 0.290.390.36 IPSL-CM4 0.190.220.56 MIROC3.2(hires) 0.350.00.12 MIROC3.2(medres) 0.330.050.20 MRI-CGCM2.3.2 -0.24-0.340.07 PCM -0.19-0.01-0.25 UKMO-HadCM3 0.370.50-0.08 UKMO-HadGEM1 0.440.120.34

18. 18 Changes in 850 hPa winds and rainfall (1980-1999) – (1951-1970) The GFDL and Hadley Centre model produced a weakened EASM ! GFDL-CM2.1HadGEM1 HadCM3CCSM3

19. 19 PDF of the weakened EASM in GFDL model The EASM weakening should be a forced signal in GFDL model. Trend of the ESAM Index Frequency EASM trend for 1950-99 in 20th century run PDF from control run

20. 20  Many models have reasonable performances in producing the main monsoon circulations such as the East Asian westerly jet, the western Pacific subtropical high and the low level monsoon circulations. The GFDL model seems to have the best performance.  The decadal variations of the EASM in ten models have significant correlations with observations during 1880-1999.  For 1950-1999, the EASM indices of nine models are significantly correlated with the observations at time scales longer than 10 years.  Only a small number of models, namely the GFDL-CM2.1, IPSL-CM4, and HadCM3, have successfully produced the recent weakening trend of the EASM.  The weakening trend of the EASM in GFDL-CM2.1 is shown to be a forced-signal rather than model internal variability. Summary

21. 21  Many models have reasonable performances in producing the main monsoon circulations such as the East Asian westerly jet, the western Pacific subtropical high and the low level monsoon circulations. The GFDL model seems to have the best performance.  The decadal variations of the EASM in ten models have significant correlations with observations during 1880-1999.  For 1950-1999, the EASM indices of nine models are significantly correlated with the observations at time scales longer than 10 years.  Only a small number of models, namely the GFDL-CM2.1, IPSL-CM4, and HadCM3, have successfully produced the recent weakening trend of the EASM.  The weakening trend of the EASM in GFDL-CM2.1 is shown to be a forced-signal rather than model internal variability. Summary

22. 22  Many models have reasonable performances in producing the main monsoon circulations such as the East Asian westerly jet, the western Pacific subtropical high and the low level monsoon circulations. The GFDL model seems to have the best performance.  The decadal variations of the EASM in ten models have significant correlations with observations during 1880-1999.  For 1950-1999, the EASM indices of nine models are significantly correlated with the observations at time scales longer than 10 years.  Only a small number of models, namely the GFDL-CM2.1, IPSL-CM4, and HadCM3, have successfully produced the recent weakening trend of the EASM.  The weakening trend of the EASM in GFDL-CM2.1 is shown to be a forced-signal rather than model internal variability. Summary

23. 23  Many models have reasonable performances in producing the main monsoon circulations such as the East Asian westerly jet, the western Pacific subtropical high and the low level monsoon circulations. The GFDL model seems to have the best performance.  The decadal variations of the EASM in ten models have significant correlations with observations during 1880-1999.  For 1950-1999, the EASM indices of nine models are significantly correlated with the observations at time scales longer than 10 years.  Only a small number of models, namely the GFDL-CM2.1, IPSL-CM4, and HadCM3, have successfully produced the recent weakening trend of the EASM.  The weakening trend of the EASM in GFDL-CM2.1 is shown to be a forced-signal rather than model internal variability. Summary

24. 24  Many models have reasonable performances in producing the main monsoon circulations such as the East Asian westerly jet, the western Pacific subtropical high and the low level monsoon circulations. The GFDL model seems to have the best performance.  The decadal variations of the EASM in ten models have significant correlations with observations during 1880-1999.  For 1950-1999, the EASM indices of nine models are significantly correlated with the observations at time scales longer than 10 years.  Only a small number of models, namely the GFDL-CM2.1, IPSL-CM4, and HadCM3, have successfully produced the recent weakening trend of the EASM.  The weakening trend of the EASM in GFDL-CM2.1 is shown to be a forced-signal rather than model internal variability. Summary

25. 25 Thank you ！ http://web.lasg.ac.cn/CSMDA/papers/017.pdf http://web.lasg.ac.cn/FGCM/publ/ztj2006a.pdf Zhou Tianjun and Rucong Yu, 2006, Twentieth Century Surface Air Temperature over China and the Globe Simulated by Coupled Climate Models, Journal of Climate, 19(22), 5843-5858.

26. 26 1.Zhou Tianjun, Aiguo Dai, and Rucong Yu, 2007, The 20th century East Asian summer monsoon simulated by coupled climate models of IPCC AR4, a manuscript 2.Yu R.C., and T.J. Zhou, 2007, Seasonality and three-dimensional structure of the interdecadal change in East Asian monsoon, Journal of Climate, in press 3. Zhou Tianjun and Rucong Yu, 2006, Twentieth Century Surface Air Temperature over China and the Globe Simulated by Coupled Climate Models, Journal of Climate, 19(22), 5843-5858. 4. Xin Xiaoge, Rucong Yu, Tianjun Zhou, and Bin Wang, 2006, Drought in Late Spring of South China in Recent Decades, Journal of Climate, 19(13), 3197-3206. 5. Zhou, T.-J., and R.-C. Yu (2005), Atmospheric water vapor transport associated with typical anomalous summer rainfall patterns in China, J. Geophys. Res., 110, D08104, doi:10.1029/2004JD005413 6.Li Jian, Rucong Yu, Tianjun Zhou, et al. 2005, Why is there an early Spring cooling shift downstream of the Tibetan Plateau, Journal of Climate, 18 (22), 4660–4668 7. Yu Rucong, Bin Wang, and Tianjun Zhou, 2004, Tropospheric cooling and summer monsoon weakening trend over East Asia, Geophysical Research Letters, 31,L22212, doi:10.1029 /2004GL021270 8. Yu Rucong, Tianjun Zhou, 2004, Impacts of winter-NAO on March cooling trends over subtropical Eurasia continent in the recent half century, Geophysical Research Letters, 31, L12204, doi:10.1029/2004GL019814. Reference for Inter-decadal variability of East Asian climate