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

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

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

PDO is in cold phase Cold Warm

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~ ~2012

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

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

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, Atmos. Scien. (Chinese) More snow less snow

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 snow cover over Eurasia precipitation anomaly 500 hPa geopotential height

Zhao et al., 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

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

More northward for WNPSH, less rainfall in Yangtze River valley Correlation between summer rainfall and axis position of WNPSH

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.

Precipitation prediction in JJA 2013 more less

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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

EASM will be a little stronger than normal Precursor of EASM (I F ) ： I F =U 200 （ E, ） - U 200 （ W, N ） R = 0.66 （ ） Strong EASM Weak EASM Zhang Q Y et al., 2003, Acta Metero. Sinica (Chinese)

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

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