1. Seasonal Climate Outlook for Summer 2013 Ke Zongjian, Wang Yongguang Beijing Climate Center 2013.04.09

2. BCC-CGCM forecast ROC area (above) Probability forecast for precipitation

3. Statistical correction to Dynamical model FODAS FODAS forecast based on BCC-CGCM and statistical methods-Feng G L et al MODES forecast based on four models and statistical methods-Liu C Z et al MODES Forecast ACC

4. PDO is in cold phase Cold Warm

5. 50 年代 60 年代 70 年代 80 年代 90 年代 21 世纪 Decadal variation of PDO and summer rain belt 1950s 1960s1970s1980s 1990s 2000~2008 2009~2012

6. 1.Influencing factor —SST Forecasted SST by dynamical models SST anomaly in last winter  Tropical SST is not conducive for western North Pacific subtropical high (WNPSH) to be very strong or weak

7. 2. influencing factor—snow cover Snow anomaly over Northern hemisphere in DJF Eurasia Tibetan Plateau Northeast China

8. Less snow cover over Tibetan Plateau in winter and spring Sensible heat is stronger and ascending activity is stronger in spring and summer Stronger heating in troposphere warm the air Thermodynamic difference increases between Tibetan Plateau and southern Sea Stronger East Asian summer monsoon (EASM, Zhang Q Y et al., 2003) More rainfall in North China, South China while less rainfall in Yangtze River valley. Less snow cover over Tibetan Plateau, less rainfall in Yangtze River valley 2.1 snow cover over Tibetan Plateau Zhang S L et al, 2001. Atmos. Scien. (Chinese) More snow less snow + - - + - +

9. More snow cover over eastern Siberia in winter, less rainfall in Yangtze River valley Xu L Y and Wu B Y ， 2012 ， Chinese J. Atmos. Sci.  More snow cover over eastern Siberia in winter will result in more thawy snow in spring. The anomaly mode of thawy snow over eastern Siberia is accordant with variation of EASM. More thawy snow will trigger longitudinal negative-positive-negative anomaly wave train of 500 hPa geopotential height in East Asia. It will strengthen EASM and result in less rainfall in Yangtze River valley. - - + 2.2 snow cover over Eurasia precipitation anomaly 500 hPa geopotential height

10. Zhao et al., 2004. J. C. Mechanism Wu B Y et al ， 2004 ， Polar res.(Chinese) More Bering sea ice, less rainfall in Yangtze River valley 3.Influencing factor– sea ice Less ice in Barents Sea, Kara Sea in winter, more ice in Bering Sea in spring Difference of rainfall between less ice and more ice Sea ice anomaly over Northern hemisphere in DJF

11. Interannual variation of Western North Pacific Subtropical High (WNPSH) in JJA Axis position Intensity west boundary jul-Aug

12. More northward for WNPSH, less rainfall in Yangtze River valley 1981-2010 Correlation between summer rainfall and axis position of WNPSH

13. Summary  WNPSH will be slightly stronger and northward than normal  EASM will be stronger than normal  More precipitation will be in North China, while less precipitation along the Yangtze River valley.

14. Precipitation prediction in JJA 2013 more less

15. Thanks for your attention!

16. EASMI I EASM =  U850 (10 ～ 20N,100 ～ 150E) -  U850 (25 ～ 35N,100 ～ 150E) Zhang Q Y et al., 2003, Acta Metero. Sinica (Chinese) Bin wang et al., 2008 ， J. C. How to represent East Asian summer monsoon

17. EASM will be a little stronger than normal Precursor of EASM (I F ) ： I F =U 200 （ 80-110E, 32.5-37.5 ） - U 200 （ 150-120W, 22.5-27.5N ） R = 0.66 （ 1981-2010 ） Strong EASM Weak EASM Zhang Q Y et al., 2003, Acta Metero. Sinica (Chinese)

18. Stronger East Asian summer monsoon, less rainfall in Yangtze River valley Corr. between summer rainfall and EASM

19. WNPSH in JJA from dynamical models IAP9L blue dashed line, climatology IAP2L red line, climatology BCC-CGCM1 red line, climatology  WNPSH is stronger and more westward than climatology