Seasonal Climate Outlook for Summer 2013

Ke Zongjian, Wang Yongguang

Beijing Climate Center

2013.04.09

BCC-CGCM forecast

ROC area (above)Probability forecast for

precipitation

Statistical correction to Dynamical modelFODAS

FODAS forecast based on BCC-CGCM and statistical methods-Feng G L et alMODES forecast based on four models and statistical methods-Liu C Z et al

MODES

Forecast

ACC

PDO is in cold phase

ColdWarm

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 1960s 1970s 1980s 1990s 2000~2008 2009~2012

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, 2001. 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.

--

+

2.2 snow cover over Eurasia

precipitation anomaly500 hPa geopotential height

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

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

1981-2010

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

moremore

more

more

more

less

Thanks for your attention!

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.

How to represent East Asian summer monsoon

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)

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