Seasonal Climate Outlook for Summer 2013

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

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

3. Statistical correction to Dynamical model MODES FODAS Forecast ACC 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

4. PDO is in cold phase Warm Cold

5. Decadal variation of PDO and summer rain belt 2009~2012 1990s 1950s 1960s 1970s 1980s 2000~2008 50年代 60年代 70年代 80年代 90年代 21世纪

6. 1.Influencing factor —SST SST anomaly in last winter Forecasted SST by dynamical models • 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. 2.1 snow cover over Tibetan Plateau Less snow cover over Tibetan Plateau, less rainfall in Yangtze River valley • 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 More snow + - - + + - Zhang S L et al, 2001. Atmos. Scien. (Chinese)

9. 2.2 snow cover over Eurasia More snow cover over eastern Siberia in winter, less rainfall in Yangtze River valley 500 hPa geopotential height precipitation anomaly - + - • 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.

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

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

15. Thanks for your attention!

16. How to represent East Asian summer monsoon EASMI IEASM =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.

17. EASM will be a little stronger than normal Precursor of EASM (IF)： IF =U200（80-110E,32.5-37.5） - U200（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 BCC-CGCM1 red line,climatology IAP2L red line,climatology IAP9L blue dashed line, climatology • WNPSH is stronger and more westward than climatology